View allAll Photos Tagged Calibration
Berlin-Tegel Airport, Germany (EDDT/TXL),
November 08, 2014,
Flight Calibration Services, D-CFME, Beech 350 Super King Air, cn FL-627
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
Calibration meter on the wall
Higashi-Nakano, Nakano-ku, Tokyo
Nikon FM
Ai Nikkor 85mm f2
Lomography Earl grey iso 100
Epson GT-X820
UGA’s Glen Harris calibrates his soil testing machine during his Soils and Hydrology Lab at the Bowen Farm in Tifton, Georgia.
By Clint Thompson
9-27-19
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
Calibrating the frame spacing on my Kiev 6C medium format SLR...
I did this before I took any pictures with this camera. I also had to take the lens apart, because the aperture blades had got jammed... it's all working now :)
How do you get the metal tungsten ball under the ship? Very carefully. Placing the ball underneath the ship (and underneath the split beam sonar) involves the coordinated effort of a large number of people maneuvering several lines tied to the ball. Here, Chief Bosun Greg Walker coordinates his movement via radio with a crewmember on the starboard side of the ship. Able Seaman Eloy Borges, behind Walker, guides a rope under the ship that is tied to a monofilament string attached to the tungsten ball. Phew! This team effort was well underway even before the sun came up.
Learn more: oceanservice.noaa.gov/caribbean-mapping/
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
the Flat Cube is my last self made astronomy device done for performing the best possible flat field calibration image. Inspired by L. Comolli project I have done my self modification in a more reduced structure more solid (made of wood) more reflective (inside there's a particular reflective surface) powered by 12v dc it has two serial dimmer (one in the back side of the "cube" one in the cable) with this combination is possible to set every kind of light intensity needed for any kind of canera ccd and filter (the light Kelvin is about 4000k real white perfect also for color DSRL or CCD) two parallel opal white plexyglass homogenize the internal light.done!
Using two additional thermometers to calibrate the PID controller's probe.
(In the photo, all the thermometers were reading different temperatures because the water was changing temperature rapidly)
On the left is my Fluke 179 meter with thermocouple, on the right is a cheap probe thermometer I use frequently when cooking :)
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
Flight Calibration Services' Diamond DA-62 'Twin Star' G-GBAS on the apron at Shoreham
An upgraded and longer-range version of their DA42 Twin Star, along with another DA-62, she recently joined FCSL's fleet of a
DA-42 and three PA-31 Piper Chieftains
DSCN7742
Aerial survey Calibration and Conformity training. Back left: Jeff Moore (WDNR), Jeff Jenkins (USFS), Rayburn Mitchell (USFS), Mike McWilliams (ODF), Keith Sprengel (USFS) and Dave Overhulser (ODF). Middle left: Ellen Michaels Goheen (USFS), Yolanda Barnett (USFS), and Beth Willhite (USFS). Front: Carrie Burns (WDNR) and Roy Magelssen (USFS).
Photo by: Unknown
Date: 2000
Credit: USDA Forest Service, Region 6, State and Private Forestry, Forest Health Protection.
Source: Aerial Survey Program collection.
For geospatial data collected during annual aerial forest insect and disease detection surveys see: www.fs.usda.gov/detail/r6/forest-grasslandhealth/insects-...
For related historic program documentation see:
archive.org/details/AerialForestInsectAndDiseaseDetection...
Johnson, J. 2016. Aerial forest insect and disease detection surveys in Oregon and Washington 1947-2016: The survey. Gen. Tech. Rep. R6-FHP-GTR-0302. Portland, OR: USDA Forest Service, Pacific Northwest Region, State and Private Forestry, Forest Health Protection. 280 p.
For additional historic forest entomology photos, stories, and resources see the Western Forest Insect Work Conference site: wfiwc.org/content/history-and-resources
Image provided by USDA Forest Service, Region 6, State and Private Forestry, Forest Health Protection: www.fs.usda.gov/main/r6/forest-grasslandhealth
Edited MODIS Terra calibration image of the Moon.
Image source: earthobservatory.nasa.gov/IOTD/view.php?id=90764
Original caption: NASA’s Terra satellite was built to observe Earth, and for more than 17 years its imagers have looked downward for 24 hours a day, collecting images needed to study the planet’s surface, oceans, and atmosphere. However, the satellite recently trained its eyes on a different celestial body.
On August 5, 2017, Terra made a partial somersault, rotating its field of view away from Earth to briefly look at the Moon and deep space. This “lunar maneuver” was choreographed to allow the mission team to recalibrate Terra’s imagers—the Moderate Resolution Imaging Spectroradiometer (MODIS), the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and the Multi-angle Imaging SpectroRadiometer (MISR). The Terra operations team last made such a maneuver in 2003.
The orbital gymnastics are necessary for radiometric calibration; that is, making sure MODIS, MISR, and ASTER are properly recording the amount of light emitted and reflected by surfaces on Earth. In the harsh environment of space, satellite instruments are bombarded by high-energy particles, cosmic rays, and strong ultraviolet light, and this inevitably leads to degradation in the sensors over time. If changes in sensitivity are not properly accounted for, the images would start to make it appear as if Earth were growing darker or lighter—which would throw off scientific efforts to characterize air pollution, cloud cover, and other elements of the environment.
The lunar surface provides a good eye test for the imagers. “The Moon is like a standard candle or lamp: the amount of energy from it is well known,” said Kurt Thome, project scientist for Terra. “If you look at it periodically, it allows you to see if your instruments are changing over time.”
Since the Moon’s surface brightness has been stable over the 17-year life of the mission—and, in fact, for thousands of years—the images of the lunar surface can be used as a standard for calibration. Terra can also observe the Moon without any atmospheric effects (such as turbulence, scattering, and absorption), which can add significant uncertainty in measured values.
The image at the top of the page was acquired by ASTER, while MODIS acquired the second image. MODIS has actually been looking at the Moon monthly for nearly its entire mission, but MISR and ASTER do not have this capability or proper angles for such a view. “MODIS can peek out of the corner and get a view of the Moon,” Thome said. “For MODIS, it has been a great way to understand the instrument over its lifetime and notice any changes.”
The nine images below come from MISR’s nine imagers. The MISR operations team uses several methods to calibrate the data regularly, all of which involve imaging something with a known (or independently measured) brightness and correcting the images to match that brightness. Every month, MISR views two panels of a special material called Spectralon, which reflects sunlight in a very particular way. ASTER, meanwhile, views a set of lamps that light up its reflective bands. Periodically, this calibration is checked by a team on the ground that measures the brightness of a flat, uniformly colored surface on Earth (such as a dry desert lakebed) while MISR and ASTER fly overhead. The lunar maneuver offers a third opportunity to check the brightness calibration of MISR.
When viewing Earth, MISR’s cameras are fixed at nine different angles, with one (called An) pointed straight down, four pointed forwards (Af, Bf, Cf, and Df) and four angled backwards (Aa, Ba, Ca, and Da). The A, B, C, and D cameras have different focal lengths, with the most oblique (D) cameras having the longest focal lengths in order to preserve spatial resolution on the ground. During the lunar maneuver, however, the spacecraft rotated so that each camera saw the almost-full Moon straight on. This means that the different focal lengths produce images with different resolutions (D cameras produce the sharpest). These grayscale images were made with raw data from the red spectral band of each camera.
After 17 years of collecting valuable data and dwindling fuel supplies, Terra is nearing the end of the mission, but not before it double-checks its data one last time. The lunar calibration is important not only for the accuracy of Terra’s instruments, but also providing data that are used to calibrate other satellites (including weather).
NASA images by Michael Abrams (NASA/JPL), Abbey Nastan (NASA/JPL), and Jesse Allen, using data from the ASTER, MISR, and MODIS instruments on the Terra satellite. Story by Tassia Owen, Abbey Nastan, and Michael Carlowicz.
Instrument(s):
Terra - ASTER
Terra - MODIS
Terra - MISR
"Saturn I booster static test stand, East Area, Test Division."
Note the Saturn I booster in the Static Test Tower/Facility Number 4572/T-Stand/Propulsion and Structural Test Facility (it had many names), foreground, lower right.
Circa 1963, possibly earlier? I'm sure the construction of the building in the center of the test stands is a clue as to the year. No idea what it is though...yet.
Roughly clockwise from the T-Stand, the other test stands visible are:
The J-2 Test Stand, the F-1 Engine Test Stand, the Saturn I Dynamic Test Stand (with the large cleared/red clay area immediately behind it - home of the future Saturn V Dynamic Test Stand) and the Cold Calibration Test Stand.
The development laboratories, assembly & checkout buildings...to include the famous 4700 ‘block’
(seen here during the 1950's):
huntsvillehistorycollection.org/hh/images/6/6e/1950s_4700...
(and in 1963):
huntsvillehistorycollection.org/hh/images/9/9b/Msfc-ra-02...
can be seen toward the horizon to the left.
Compare/contrast to a similar view from 1992:
huntsvillehistorycollection.org/hh/hhpics/msfc/msfc-maps/...
Huntsville History Collection website
This handle makes it easy to reach deeply into the 3D printer while calibrating and levelling the build platform. It is designed to hold a standard Post-it sticky paper on it's tip.
In most cases the optimal gap between a 3D printer's platform and the extruder's hot-end tip, is 0,1 mm. A common practice is to use a simple sheet of paper and place it on top of the build platform just under the extruder's tip.
The platform is then adjusted to only just let the paper slide freely. The adjustment must be made on all corners and the centre of the build plate until it is perfectly level.
• Download the STL file
• 3D-print it
• Grab a Post-it sticky of your preferred colour
• Stick it on the flat front end of the 3D-printed handle
• Set-up you 3D-printer for levelling the platform
• Place the paper between the the platform and the extruder tip
• Adjust the build plate's screws and move the handle slightly to make the paper slide under the extruder tip
• When you feel a slight friction stop adjusting the screw
• Repeat this process on all corners and centre of the platform until you can feel the same friction on all spots
Make sure that you only use one sheet of Post-it paper and if unsure control-measure it with a calliper to verify 0.1 mm thickness.
After calibrating your Replicator's platform it should remain level for a long time. Until you need to calibrate it next time you can use this Post-it handle for other purposes as follows:
• A very gentle fly-swat (PETA-certified ;)
• A small sign holder you can use to communicate short messages to your office mates
You can download the 3D file for this handle from:
www.thingiverse.com/thing:69656
It was printed on a makerbot.creativetools.se
Humidity and temperature calibration mean the instruments which are used to measure temperature should measure the climatic conditions accurately. Temperature is measured in Celsius or Fahrenheit with the help of thermometer and humidity is the amount of water present in air measure with the help of humidity detector or humidity gauge. ivscanada.ca/pages/humidity-temperature
A repro (with color film chain calibration approximation to match) of the first color test pattern (a custom-made design) of NBC-owned WNBC-TV (Channel 4) in New York as inaugurated in 1975. In this form, it initially lasted only a few months on the air prior to sign-on, up to the introduction of the 'N' logo in 1976; however, from the mid-1980's to the early 1990's the station used this particular version of this TP before signing on. If this pattern were misaligned, the 1947 copyright from NBC could be seen below the pattern. As seen on a now-defunct TV DX website and a YouTube clip.
Title: Technician at work, UV-634 Atomic Absorption Spectrophotometer mono calibration, Varian Techtron, 679 Springvale Road, Mulgrave
Author / Creator: Sievers, Wolfgang, 1913-2007 photographer.
Date: 1974.
Varian Techtron was the result of a merger between the Australian company Techtron and the American firm Varian Associates in 1967. The Springvale Road site (then in Springvale North, but now in Mulgrave) was established by Techtron and is still in use, but now as Agilent Technologies (which acquired Varian in 2009). Techtron Appliances was established in 1938 and it and its successor companies have produced a variety of electronic and analytic equipment for industry and scientific research, notably including Atomic Absorption Spectrophotometers (AAS) to CSIRO specifications.
See locale on Google Maps.
Subjects:
Varian Techtron Employees.
Atomic absorption spectroscopy Calibration.
Atomic absorption spectroscopy Instruments.
Industrial technicians.
Portrait photographs.
Gelatin silver prints.
Index terms:
Australia; Victoria; Wolfgang Sievers; Mulgrave; technicians; atomic absorption spectroscopy; Varian Techtron
Notes:
Job number inscribed in pencil on reverse of image: 4314 AE
Vintage print with the photographer's studio stamp on reverse.
Title taken from information supplied by Varian Australia, courtesy of the photographer.
Printed by Wolfgang Sievers at an unknown date from his negative made in 1974.
Copyright status: This work is in copyright
Conditions of use: Copyright restrictions apply.
For Copyright queries, please contact the National Library of Australia.
Source: SLV
Identifier(s): Accession no: H2000.195/244
Source / Donor: Purchased 2000.
Series / Collection: Wolfgang Sievers collection.
Link to online item:
handle.slv.vic.gov.au/10381/308721
Link to this record:
search.slv.vic.gov.au/permalink/f/1fe7t3h/SLV_ROSETTAIE18...
search.slv.vic.gov.au/permalink/f/1fe7t3h/SLV_VOYAGER1757464
This is after repairing the following:
-Soaking seized focusing ring in lighter fluid for a week to unscrew it. Then applied new synthetic, high-viscosity grease.
-Dismantling and cleaning the shutter mechanism and blades.
-Cleaning aperture blades.
-Cleaning inside viewfinder and light meter glass.
-Replaced a stripped gear that resets the double-exposure guard on the shutter release.
-Replaced one of the springs that flip the front forward.
Tested the light meter accuracy and shutter speeds. Both still work exceptionally well for 60+ years old.
Cut a plastic bag into a strip and rolled it to use as an easy focus test. Calibrated to infinity.
UPDATE: Tested camera. Seems to be working ok. Test photos below:
Globular Cluster (Messier 3) in Canes Venatici captured 16 May 2022, ~22:00 hrs ET, Springfield, VA, USA. Bortle 8 skies, Celestron 8 inch SCT at f/6.3 (eff. fl 1290mm), Orion Atlas AZ/EQ-G Pro mount. QHY 294M Pro camera @ -10C, bin 1, exposure 32 seconds, gain 3100, 11MP mode, stack of 20 subframes, no calibration frames used. Baader Luminance filter.
Clouds: clear
Seeing: avg
Transparency: avg
Moon phase: full
FOV: 33 x 33 arcmin.
Resolution: 1.0 arcsec/pixel.
Orientation: Up is East.
From Wikipedia:
A globular cluster is a spherical collection of stars. Globular clusters are very tightly bound by gravity, with a high concentration of stars towards their centers. Their name is derived from Latin globulus—a small sphere. Globular clusters are occasionally known simply as globulars.
Although one globular cluster, Omega Centauri, was observed in antiquity and long thought to be a star, recognition of the clusters' true nature came with the advent of telescopes in the 17th century. In early telescopic observations, globular clusters appeared as fuzzy blobs, leading French astronomer Charles Messier to include many of them in his catalog of astronomical objects that he thought could be mistaken for comets. Using larger telescopes, 18th-century astronomers recognized that globular clusters are groups of many individual stars. Early in the 20th century, the distribution of globular clusters in the sky was some of the first evidence that the Sun is far from the center of the Milky Way.
Globular clusters are found in nearly all galaxies. In spiral galaxies like the Milky Way, they are mostly found in the outer, spheroidal part of the galaxy—the galactic halo. They are the largest and most massive type of star cluster, tending to be older, denser, and composed of fewer heavy elements than open clusters, which are generally found in the disks of spiral galaxies. The Milky Way has over 150 known globulars, and there may be many more.
The origin of globular clusters and their role in galactic evolution are unclear. Some are among the oldest objects in their galaxies and even the universe, constraining estimates of the universe's age. Star clusters are often assumed to consist of stars that all formed at the same time from one star-forming nebula, but nearly all globular clusters contain stars that formed at different times, or that have differing compositions. Some clusters may have had multiple episodes of star formation, and some may be remnants of smaller galaxies captured by larger galaxies.
The first known globular cluster, now called M22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, then finally as a globular cluster in the early 19th century by John Herschel. The French astronomer Abbé Lacaille listed NGC 104, NGC 4833, M55, M69, and NGC 6397 in his 1751–1752 catalogue. The low resolution of early telescopes prevented individual stars in a cluster from being visually separated until Charles Messier observed M4 in 1764.
When William Herschel began his comprehensive survey of the sky using large telescopes in 1782, there were 34 known globular clusters. Herschel discovered another 36 and was the first to resolve virtually all of them into stars. He coined the term globular cluster in his Catalogue of a Second Thousand New Nebulae and Clusters of Stars (1789). In 1914, Harlow Shapley began a series of studies of globular clusters, published across about 40 scientific papers. He examined the clusters' RR Lyrae variables—stars which he assumed were Cepheid variables—and used their luminosity and period of variability to estimate the distances to the clusters. It was later found that RR Lyrae variables are fainter than Cepheid variables, causing Shapley to overestimate the distances.
A large majority of the Milky Way's globular clusters are found in the celestial sky around the galactic core. In 1918, Shapley used this strongly asymmetrical distribution to determine the overall dimensions of the galaxy. Assuming a roughly spherical distribution of globular clusters around the galaxy’s center, he used the positions of the clusters to estimate the position of the Sun relative to the galactic center. He correctly concluded that the Milky Way's center is in the Sagittarius constellation and not near the Earth. He overestimated the distance, finding typical globular cluster distances of 10–30 kiloparsecs (33,000–98,000 ly); the modern distance to the galactic center is roughly 8.5 kiloparsecs (28,000 ly). Shapley's measurements indicated the Sun is relatively far from the center of the galaxy, contrary to what had been inferred from the observed uniform distribution of ordinary stars. In reality, most ordinary stars lie within the galaxy's disk and are thus obscured by gas and dust in the disk, whereas globular clusters lie outside the disk and can be seen at much further distances.
The count of known globular clusters in the Milky Way has continued to increase, reaching 83 in 1915, 93 in 1930, 97 by 1947, and 157 in 2010. Additional, undiscovered globular clusters are believed to be in the galactic bulge or hidden by the gas and dust of the Milky Way. The Andromeda Galaxy—comparable in size to the Milky Way—may have as many as 500 globulars. Every galaxy of sufficient mass in the Local Group has an associated system of globular clusters, as does almost every large galaxy surveyed. Some giant elliptical galaxies (particularly those at the centers of galaxy clusters), such as M87, have as many as 13,000 globular clusters.
Shapley was later assisted in his studies of clusters by Henrietta Swope and Helen Sawyer Hogg. In 1927–1929, Shapley and Sawyer categorized clusters by the degree of concentration of stars toward each core. Their system, known as the Shapley–Sawyer Concentration Class, identifies the most concentrated clusters as Class I and ranges to the most diffuse Class XII. In 2015, astronomers from the Pontifical Catholic University of Chile proposed a new type of globular cluster on the basis of observational data: dark globular clusters.
The formation of globular clusters is poorly understood.
Globular clusters have traditionally been described as a simple star population formed from a single giant molecular cloud, and thus with roughly uniform age and metallicity (proportion of heavy elements in their composition). Modern observations show that nearly all globular clusters contain multiple populations; the globular clusters in the Large Magellanic Cloud (LMC) exhibit a bimodal population, for example. During their youth, these LMC clusters may have encountered giant molecular clouds that triggered a second round of star formation. This star-forming period is relatively brief, compared with the age of many globular clusters. It has been proposed that this multiplicity in stellar populations could have a dynamical origin. In the Antennae Galaxy, for example, the Hubble Space Telescope has observed clusters of clusters—regions in the galaxy that span hundreds of parsecs, in which many of the clusters will eventually collide and merge. Their overall range of ages and (possibly) metallicities could lead to clusters with a bimodal, or even multiple, distribution of populations.
Observations of globular clusters show that their stars primarily come from regions of more efficient star formation, and from where the interstellar medium is at a higher density, as compared to normal star-forming regions. Globular cluster formation is prevalent in starburst regions and in interacting galaxies. Some globular clusters likely formed in dwarf galaxies and were removed by tidal forces to join the Milky Way. In elliptical and lenticular galaxies there is a correlation between the mass of the supermassive black holes (SMBHs) at their centers and the extent of their globular cluster systems. The mass of the SMBH in such a galaxy is often close to the combined mass of the galaxy's globular clusters.
No known globular clusters display active star formation, consistent with the hypothesis that globular clusters are typically the oldest objects in their galaxy and were among the first collections of stars to form. Very large regions of star formation known as super star clusters, such as Westerlund 1 in the Milky Way, may be the precursors of globular clusters.
Many of the Milky Way's globular clusters have a retrograde orbit, including the most massive, Omega Centauri. Its retrograde orbit suggests it may be a remnant of a dwarf galaxy captured by the Milky Way.
Globular clusters are generally composed of hundreds of thousands of low-metal, old stars. The stars found in a globular cluster are similar to those in the bulge of a spiral galaxy but confined to a spheroid in which half the light is emitted within a radius of only a few to a few tens of parsecs. They are free of gas and dust and it is presumed that all of the gas and dust was long ago either turned into stars or blown out of the cluster by the massive first-generation stars.
Globular clusters can contain a high density of stars; on average about 0.4 stars per cubic parsec, increasing to 100 or 1000 stars/pc3 in the core of the cluster. In comparison, the stellar density around the sun is roughly 0.1 stars/pc3. The typical distance between stars in a globular cluster is about 1 light year, but at its core the separation between stars averages about a third of a light year—13 times closer than Proxima Centauri, the closest star to the Sun.
Globular clusters are thought to be unfavorable locations for planetary systems. Planetary orbits are dynamically unstable within the cores of dense clusters because of the gravitational perturbations of passing stars. A planet orbiting at 1 astronomical unit around a star that is within the core of a dense cluster, such as 47 Tucanae, would only survive on the order of 100 million years. There is a planetary system orbiting a pulsar (PSR B1620−26) that belongs to the globular cluster M4, but these planets likely formed after the event that created the pulsar.
Some globular clusters, like Omega Centauri in the Milky Way and Mayall II in the Andromeda Galaxy, are extraordinarily massive, measuring several million solar masses (M☉) and having multiple stellar populations. Both are evidence that supermassive globular clusters are in fact the cores of dwarf galaxies that have been consumed by larger galaxies. About a quarter of the globular cluster population in the Milky Way may have been accreted this way, as with more than 60% of the globular clusters in the outer halo of Andromeda.
Globular clusters normally consist of Population II stars which, compared with Population I stars such as the Sun, have a higher proportion of hydrogen and helium and a lower proportion of heavier elements. Astronomers refer to these heavier elements as metals (distinct from the material concept) and to the proportions of these elements as the metallicity. Produced by stellar nucleosynthesis, the metals are recycled into the interstellar medium and enter a new generation of stars. The proportion of metals can thus be an indication of the age of a star in simple models, with older stars typically having a lower metallicity.
The Dutch astronomer Pieter Oosterhoff observed two special populations of globular clusters, which became known as Oosterhoff groups. The second group has a slightly longer period of RR Lyrae variable stars. While both groups have a low proportion of metallic elements as measured by spectroscopy, the metal spectral lines in the stars of Oosterhoff type I (Oo I) cluster are not quite as weak as those in type II (Oo II), and so type I stars are referred to as metal-rich (e.g. Terzan 7), while type II stars are metal-poor (e.g. ESO 280-SC06). These two distinct populations have been observed in many galaxies, especially massive elliptical galaxies. Both groups are nearly as old as the universe itself and are of similar ages. Suggested scenarios to explain these subpopulations include violent gas-rich galaxy mergers, the accretion of dwarf galaxies, and multiple phases of star formation in a single galaxy. In the Milky Way, the metal-poor clusters are associated with the halo and the metal-rich clusters with the bulge.
In the Milky Way, a large majority of the metal-poor clusters are aligned on a plane in the outer part of the galaxy's halo. This observation supports the view that type II clusters were captured from a satellite galaxy, rather than being the oldest members of the Milky Way's globular cluster system—as was previously thought. The difference between the two cluster types would then be explained by a time delay between when the two galaxies formed their cluster systems.
Close interactions and near-collisions of stars occur relatively often in globular clusters because of their high star density. These chance encounters give rise to some exotic classes of stars—such as blue stragglers, millisecond pulsars, and low-mass X-ray binaries—which are much more common in globular clusters. How blue stragglers form remains unclear, but most models attribute them to interactions between stars, such as stellar mergers, the transfer of material from one star to another, or even an encounter between two binary systems. The resulting star has a higher temperature than other stars in the cluster with comparable luminosity and thus differs from the main sequence stars formed early in the cluster's existence. Some clusters have two distinct sequences of blue stragglers, one bluer than the other.
Astronomers have searched for black holes within globular clusters since the 1970s. The required resolution for this task is exacting; it is only with the Hubble Space Telescope (HST) that the first claimed discoveries were made, in 2002 and 2003. Based on HST observations, other researchers suggested the existence of a 4,000 M☉(solar masses) intermediate-mass black hole in the globular cluster M15 and a 20,000 M☉ black hole in the Mayall II cluster of the Andromeda Galaxy. Both X-ray and radio emissions from Mayall II appear consistent with an intermediate-mass black hole; however, these claimed detections are controversial. The heaviest objects in globular clusters are expected to migrate to the cluster center due to mass segregation. One research group pointed out that the mass-to-light ratio should rise sharply towards the center of the cluster, even without a black hole, in both M15 and Mayall II. Observations from 2018 find no evidence for an intermediate-mass black hole in any globular cluster, including M15, but cannot definitively rule out one with a mass of 500–1000 M☉.
The confirmation of intermediate-mass black holes in globular clusters would have important ramifications for theories of galaxy development as being possible sources for the supermassive black holes at their centers. The mass of these supposed intermediate-mass black holes is proportional to the mass of their surrounding clusters, following a pattern previously discovered between supermassive black holes and their surrounding galaxies.
Hertzsprung–Russell diagrams (H–R diagrams) of globular clusters allow astronomers to determine many of the properties of their populations of stars. An H–R diagram is a graph of a large sample of stars plotting their absolute magnitude (their luminosity, or brightness measured from a standard distance), as a function of their color index. The color index, roughly speaking, measures the color of the star; positive color indices indicate a reddish star with a cool surface temperature, while negative values indicate a bluer star with a hotter surface. Stars on an H–R diagram mostly lie along a roughly diagonal line sloping from hot, luminous stars in the upper left to cool, faint stars in the lower right. This line is known as the main sequence and represents the primary stage of stellar evolution. The diagram also includes stars in later evolutionary stages such as the cool but luminous red giants.
Constructing an H–R diagram requires knowing the distance to the observed stars to convert apparent into absolute magnitude. Because all the stars in a globular cluster have about the same distance from Earth, a color–magnitude diagram using their observed magnitudes looks like a shifted H–R diagram—because of the roughly constant difference between their apparent and absolute magnitudes. This shift is called the distance modulus and can be used to calculate the distance to the cluster. The modulus is determined by comparing features (like the main sequence) of the cluster's color–magnitude diagram to corresponding features in an H–R diagram of another set of stars, a method known as spectroscopic parallax or main-sequence fitting.
Since globular clusters form at once from a single giant molecular cloud, a cluster's stars have roughly the same age and composition. A star's evolution is primarily determined by its initial mass, so the positions of stars in a cluster's H–R or color–magnitude diagram mostly reflect their initial masses. A cluster's H–R diagram, therefore, appears quite different from H–R diagrams containing stars of a wide variety of ages. Almost all stars fall on a well-defined curve in globular cluster H–R diagrams, and that curve's shape indicates the age of the cluster. A more detailed H–R diagram often reveals multiple stellar populations as indicated by the presence of closely separated curves, each corresponding to a distinct population of stars with a slightly different age or composition.
Observations with the Wide Field Camera 3, installed in 2009 on the Hubble Space Telescope, made it possible to distinguish these slightly different curves.
The most massive main-sequence stars have the highest luminosity and will be the first to evolve into the giant star stage. As the cluster ages, stars of successively lower masses will do the same. Therefore, the age of a single-population cluster can be measured by looking for those stars just beginning to enter the giant star stage, which form a "knee" in the H–R diagram called the main sequence turnoff, bending to the upper right from the main-sequence line. The absolute magnitude at this bend is directly a function of the cluster's age; an age scale can be plotted on an axis parallel to the magnitude.
The morphology and luminosity of globular cluster stars in H–R diagrams are influenced by numerous parameters, many of which are still actively researched. Recent observations have overturned the historical paradigm that all globular clusters consist of stars born at exactly the same time, or sharing exactly the same chemical abundance. Some clusters feature multiple populations, slightly differing in composition and age; for example, high-precision imagery of cluster NGC 2808 discerned three close, but distinct, main sequences. Further, the placements of the cluster stars in an H–R diagram—including the brightnesses of distance indicators—can be influenced by observational biases. One such effect, called blending, arises when the cores of globular clusters are so dense that observations see multiple stars as a single target. The brightness measured for that seemingly single star is thus incorrect—too bright, given that multiple stars contributed.[81] The computed distance is in turn incorrect, so the blending effect can introduce a systematic uncertainty into the cosmic distance ladder and may bias the estimated age of the universe and the Hubble constant.
The aforementioned blue stragglers appear on the H–R diagram as a series diverging from the main sequence in the direction of brighter, bluer stars. White dwarfs (the final remnants of some Sun-like stars), which are much fainter and somewhat hotter than the main sequence stars, lie on the bottom-left of an H–R diagram. Globular clusters can be dated by looking at the temperatures of the coolest white dwarfs, often giving results as old as 12.7 billion years. In comparison, open clusters are rarely older than about 500 million years. The ages of globular clusters place a lower bound on the age of the entire universe, presenting a significant constraint in cosmology. Astronomers were historically faced with age estimates of clusters older than their cosmological models would allow, but better measurements of cosmological parameters, through deep sky surveys and satellites, appear to have resolved this issue.
Studying globular clusters sheds light on how the composition of the formational gas and dust affects stellar evolution; the stars' evolutionary tracks vary depending on the abundance of heavy elements. Data obtained from these studies are then used to study the evolution of the Milky Way as a whole.
In contrast to open clusters, most globular clusters remain gravitationally bound together for time periods comparable to the lifespans of most of their stars. Strong tidal interactions with other large masses result in the dispersal of some stars, leaving behind "tidal tails" of stars removed from the cluster.
After formation, the stars in the globular cluster begin to interact gravitationally with each other. The velocities of the stars steadily change, and the stars lose any history of their original velocity. The characteristic interval for this to occur is the relaxation time, related to the characteristic length of time a star needs to cross the cluster and the number of stellar masses.[92] The relaxation time varies by cluster, but a typical value is on the order of one billion years.[93][94]
Although globular clusters are generally spherical in form, ellipticity can form via tidal interactions. Clusters within the Milky Way and the Andromeda Galaxy are typically oblate spheroids in shape, while those in the Large Magellanic Cloud are more elliptical.
Astronomers characterize the morphology (shape) of a globular cluster by means of standard radii: the core radius (rc), the half-light radius (rh), and the tidal or Jacobi radius (rt). The radius can be expressed as a physical distance or as a subtended angle in the sky. Considering a radius around the core, the surface luminosity of the cluster steadily decreases with distance, and the core radius is the distance at which the apparent surface luminosity has dropped by half. A comparable quantity is the half-light radius, or the distance from the core containing half the total luminosity of the cluster; the half-light radius is typically larger than the core radius.
Most globular clusters have a half-light radius of less than 10 parsecs (pc), although some globular clusters have very large radii, like NGC 2419 (rh = 18 pc) and Palomar 14 (rh = 25 pc). The half-light radius includes stars in the outer part of the cluster that happen to lie along the line of sight, so theorists also use the half-mass radius (rm)—the radius from the core that contains half the total mass of the cluster. A small half-mass radius, relative to the overall size, indicates a dense core. Messier 3 (M3), for example, has an overall visible dimension of about 18 arc minutes, but a half-mass radius of only 1.12 arc minutes.
The tidal radius, or Hill sphere, is the distance from the center of the globular cluster at which the external gravitation of the galaxy has more influence over the stars in the cluster than does the cluster itself. This is the distance at which the individual stars belonging to a cluster can be separated away by the galaxy. The tidal radius of M3, for example, is about 40 arc minutes, or about 113 pc.
In most Milky Way clusters, the surface brightness of a globular cluster as a function of decreasing distance to the core first increases, then levels off at a distance typically 1–2 parsecs from the core. About 20% of the globular clusters have undergone a process termed "core collapse". In such a cluster, the luminosity increases steadily all the way to the core region.
Models of globular clusters predict core collapse occurs when the more massive stars in a globular cluster encounter their less massive counterparts. Over time, dynamic processes cause individual stars to migrate from the center of the cluster to the outside, resulting in a net loss of kinetic energy from the core region and leading the region's remaining stars to occupy a more compact volume. When this gravothermal instability occurs, the central region of the cluster becomes densely crowded with stars, and the surface brightness of the cluster forms a power-law cusp. A massive black hole at the core could also result in a luminosity cusp. Over a long time this leads to a concentration of massive stars near the core, a phenomenon called mass segregation.
The dynamical heating effect of binary star systems works to prevent an initial core collapse of the cluster. When a star passes near a binary system, the orbit of the latter pair tends to contract, releasing energy. Only after this primordial supply of energy is exhausted can a deeper core collapse proceed. In contrast, the effect of tidal shocks as a globular cluster repeatedly passes through the plane of a spiral galaxy tends to significantly accelerate core collapse.
Core collapse may be divided into three phases. During a cluster's adolescence, core collapse begins with stars nearest the core. Interactions between binary star systems prevents further collapse as the cluster approaches middle age. The central binaries are either disrupted or ejected, resulting in a tighter concentration at the core. The interaction of stars in the collapsed core region causes tight binary systems to form. As other stars interact with these tight binaries they increase the energy at the core, causing the cluster to re-expand. As the average time for a core collapse is typically less than the age of the galaxy, many of a galaxy's globular clusters may have passed through a core collapse stage, then re-expanded.
The HST has provided convincing observational evidence of this stellar mass-sorting process in globular clusters. Heavier stars slow down and crowd at the cluster's core, while lighter stars pick up speed and tend to spend more time at the cluster's periphery. The cluster 47 Tucanae, made up of about one million stars, is one of the densest globular clusters in the Southern Hemisphere. This cluster was subjected to an intensive photographic survey that obtained precise velocities for nearly 15,000 stars in this cluster.
The overall luminosities of the globular clusters within the Milky Way and the Andromeda Galaxy each have a roughly Gaussian distribution, with an average magnitude Mv and a variance σ2. This distribution of globular cluster luminosities is called the Globular Cluster Luminosity Function (GCLF). For the Milky Way, Mv = −7.29 ± 0.13, σ = 1.1 ± 0.1. The GCLF has been used as a "standard candle" for measuring the distance to other galaxies, under the assumption that globular clusters in remote galaxies behave similarly to those in the Milky Way.
Computing the gravitational interactions between stars within a globular cluster requires solving the N-body problem. The naive computational cost for a dynamic simulation increases in proportion to N 2 (where N is the number of objects), so the computing requirements to accurately simulate a cluster of thousands of stars can be enormous. A more efficient method of simulating the N-body dynamics of a globular cluster is done by subdivision into small volumes and velocity ranges, and using probabilities to describe the locations of the stars. Their motions are described by means of the Fokker–Planck equation, often using a model describing the mass density as a function of radius, such as a Plummer model. The simulation becomes more difficult when the effects of binaries and the interaction with external gravitation forces (such as from the Milky Way galaxy) must also be included. In 2010 a low-density globular cluster's lifetime evolution was first directly computed, star-by-star.
Completed N-body simulations have shown that stars can follow unusual paths through the cluster, often forming loops and falling more directly toward the core than would a single star orbiting a central mass. Additionally, some stars gain sufficient energy to escape the cluster due to gravitational interactions that result in a sufficient increase in velocity. Over long periods of time this process leads to the dissipation of the cluster, a process termed evaporation. The typical time scale for the evaporation of a globular cluster is 1010 years. The ultimate fate of a globular cluster must be either to accrete stars at its core, causing its steady contraction, or gradual shedding of stars from its outer layers.
Binary stars form a significant portion of stellar systems, with up to half of all field stars and open cluster stars occurring in binary systems. The present-day binary fraction in globular clusters is difficult to measure, and any information about their initial binary fraction is lost by subsequent dynamical evolution. Numerical simulations of globular clusters have demonstrated that binaries can hinder and even reverse the process of core collapse in globular clusters. When a star in a cluster has a gravitational encounter with a binary system, a possible result is that the binary becomes more tightly bound and kinetic energy is added to the solitary star. When the massive stars in the cluster are sped up by this process, it reduces the contraction at the core and limits core collapse.
Cluster classification is not always definitive; objects have been found that can be classified in more than one category. For example, BH 176 in the southern part of the Milky Way has properties of both an open and a globular cluster.
In 2005, astronomers discovered a new, "extended" type of star cluster in the Andromeda Galaxy's halo, similar to the globular cluster. The three new-found clusters have a similar star count as globular clusters and share other characteristics, such as stellar populations and metallicity, but are distinguished by their larger size—several hundred light years across—and some hundred times lower density. Their stars are separated by larger distances; parametrically, these clusters lie somewhere between a globular cluster and a dwarf spheroidal galaxy. The formation of these extended clusters is likely related to accretion. It is unclear why the Milky Way lacks such clusters; Andromeda is unlikely to be the sole galaxy with them, but their presence in other galaxies remains unknown.
When a globular cluster comes close to a large mass, such as the core region of a galaxy, it undergoes a tidal interaction. The difference in gravitational strength between the nearer and further parts of the cluster results in an asymmetric, tidal force. A "tidal shock" occurs whenever the orbit of a cluster takes it through the plane of a galaxy.
Tidal shocks can pull stars away from the cluster halo, leaving only the core part of the cluster; these trails of stars can extend several degrees away from the cluster. These tails typically both precede and follow the cluster along its orbit and can accumulate significant portions of the original mass of the cluster, forming clump-like features. The globular cluster Palomar 5, for example, is near the apogalactic point of its orbit after passing through the Milky Way. Streams of stars extend outward toward the front and rear of the orbital path of this cluster, stretching to distances of 13,000 light years. Tidal interactions have stripped away much of Palomar 5's mass; further interactions with the galactic core are expected to transform it into a long stream of stars orbiting the Milky Way in its halo.
The Milky Way is in the process of tidally stripping the Sagittarius Dwarf Spheroidal Galaxy of stars and globular clusters through the Sagittarius Stream. As many as 20% of the globular clusters in the Milky Way's outer halo may have originated in that galaxy. Palomar 12, for example, most likely originated in the Sagittarius Dwarf Spheroidal but is now associated with the Milky Way. Tidal interactions like these add kinetic energy into a globular cluster, dramatically increasing the evaporation rate and shrinking the size of the cluster. The increased evaporation accelerates the process of core collapse.
Astronomers are searching for exoplanets of stars in globular star clusters.[141] A search in 2000 for giant planets in the globular cluster 47 Tucanae came up negative, suggesting that the abundance of heavier elements—low in globular clusters—necessary to build these planets may need to be at least 40% of the Sun's abundance. Because terrestrial planets are built from heavier elements such as silicon, iron and magnesium, member stars have a far lower likelihood of hosting Earth-mass planets than stars in the solar neighborhood. Globular clusters are thus unlikely to host habitable terrestrial planets.
A giant planet was found in the Messier 4 globular cluster orbiting a pulsar in the binary star system PSR B1620-26. The planet's eccentric and highly inclined orbit suggests it may have been formed around another star in the cluster, then "exchanged" into its current arrangement. The likelihood of close encounters between stars in a globular cluster can disrupt planetary systems; some planets break free to become rogue planets, orbiting the galaxy. Planets orbiting close to their star can become disrupted, potentially leading to orbital decay and an increase in orbital eccentricity and tidal effects.
A repro (with color film calibration approximation to match) of an early color test pattern from KYW-TV (Channel 3) in Philadelphia, PA, from around the time the station began producing their locally-originated shows in color around 1967 (the year their most famous production, The Mike Douglas Show, went color). This preceded the better-known design shown here, and in this form the pattern may have been from a leftover TP from the last years of NBC's ownership of the station as WRCV-TV. From a screencap shown within Tumblr (which, alas, represented this pattern in B&W).
It pays off to calibrate your objectives! Here's a comparison of two photos taken with Sigma 85mm f1.4 before (left) and after (right) calibration. Just look at all that texture that appeared after calibration. The objective was front focusing by a whopping 7 microunits. These photos were taken at f1.6 and they're still a bit soft due to the large aperture, but the difference is obvious.
PACIFIC OCEAN (Jan. 21, 2019) - Fire Controlman 1st Class Andrew Wilkins and Fire Controlman 3rd Class Austin Lloyd, assigned to the Arleigh Burke-class guided-missile destroyer USS Preble (DDG 88), load rounds into a Phalanx close-in weapons system (CIWS) in preparation for a calibration test. Preble is deployed to the U.S 7th Fleet area of operations in support of security and stability in the Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 1st Class Bryan Niegel) 190121-N-UI104-0019
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Focus test with new Sigma 50-150 f/2.8 II APO EX DC; center autofocus on leaf as indicated by red square, ISO 100, f/2.8. Representative sample of multiple shots.
1-113th Field Artillery Soldiers conduct calibration at the National Training Center in Fort Irwin, CA, July 5, 2019. Operation Hickory Sting is a rotation focused on combined arms maneuver and collective gunnery at the National Training Center, Fort Irwin, CA, to validate the capabilities of the 30th Armored Brigade Combat Team in the training environment and provide a globally responsive brigade ready to deploy, fight and win. (Photo by Sgt. Odaliska Almonte, North Carolina National Guard Public Affairs)
That grey square acted as both an excess heat radiator and an optical calibration target for the cameras on the Scan Platform.
Focus test with new Sigma 50-150 f/2.8 II APO EX DC; center autofocus on thick black line in center of chart; ISO 100, f/2.8, camera tripod mounted at about 45 degrees, mirror lock up, remote trigger. Representative sample of multiple shots.