Wikipedia

Star trail

"Star trails" redirects here. For the music album, seeStar Trails.

Astar trailis a type ofphotographthat useslong exposuretimes to capturediurnal circles,theapparent motionofstarsin thenight skydue toEarth's rotation.A star-trail photograph shows individual stars as streaks across the image, with longerexposuresyielding longerarcs.The term is used for similar photos captured elsewhere, such as on board theInternational Space Stationand onMars.[2][3]

All thestarsin thenight skyappear to circle thecelestial pole(the south pole in this photo). Over a period of several hours, thisapparent motionleaves star trails.[1]
Star trail photographed fromMount Wellington,Tasmania.Auroraaustralisvisible in the background.
Star trail photography on salt lake in Lut desert in Iran
Star trail photography on salt lake in Lut desert in Iran

Typicalshutter speedsfor a star trail range from 15 minutes to several hours, requiring a "Bulb"setting on the camera to open theshutterfor a period longer than usual. However, a more practiced technique is to blend a number of frames together to create the final star trail image.[4]

Star trails have been used by professionalastronomersto measure the quality ofobserving locationsfor majortelescopes.

Capture

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Star trails photographed from theInternational Space Stationinlow Earth orbitat an angle that makes the trails almost vertical instead of circular.

Star trail photographs are captured by placing a camera on atripod,pointing the lens toward thenight sky,and allowing theshutterto stay open for along periodof time.[5]Star trails are considered relatively easy for amateurastrophotographersto create.[6]Photographers generally make these images by using aDSLR or Mirrorless camerawith its lens focus set to infinity. A cable release or intervalometer allows the photographer to hold the shutter open for the desired amount of time. Typical exposure times range from 15 minutes to many hours long, depending on the desired length of the star trail arcs for the image.[7]Even though star trail pictures are created under low-light conditions, long exposure times allowfast films,such asISO200 and ISO 400.[6]Wide-apertures, such as f/5.6 and f/4, are recommended for star trails.[5][8]

The star trails captured with 136 minutes long period of exposure in Eleebana, NSW, Australia on Mar 03, 2019

Because exposure times for star trail photographs can be several hours long, camera batteries can be easily depleted. Mechanical cameras that do not require a battery to open and close the shutter have an advantage over more modern film and digital cameras that rely on battery power. On these cameras, theBulb,or B, exposure setting keeps the shutter open.[9]Another problem that digital cameras encounter is an increase in electronicnoisewith increasing exposure time.[5]However, this can be avoided through the use of shorter exposure times that are then stacked in post production software. This avoids possible heat build up or digital noise caused from a single long exposure.

American astronautDon Pettitrecorded star trails with a digital camera from theInternational Space Stationin Earth orbit between April and June, 2012. Pettit described his technique as follows: "My star trail images are made by taking a time exposure of about 10 to 15 minutes. However, with modern digital cameras, 30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures I do what many amateur astronomers do. I take multiple 30-second exposures, then 'stack' them usingimaging software,thus producing the longer exposure. "[10][2]

Star trail images have also been taken on Mars.[11]TheSpirit roverproduced them while looking for meteors.[11]Since the camera was limited to 60 second exposures the trails appear as dashed lines.[11]

Earth's rotation

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Main article:Earth's rotation
Star trail over the rocky mountain in Alamut, Qazvin, Iran

Star trail photographs are possible because ofthe rotationofEarthabout its axis. Theapparent motionof the stars is recorded as mostly curved streaks on the film or detector.[5]For observers in theNorthern Hemisphere,aiming the camera northward creates an image withconcentriccircular arcscentered on the northcelestial pole(very nearPolaris).[6]For those in theSouthern Hemisphere,this same effect is achieved by aiming the camera southward. In this case, the arc streaks are centered on the south celestial pole (nearSigma Octantis). Aiming the camera eastward or westward shows straight streaks on thecelestial equator,which is tilted at angle with respect to thehorizon.The angular measure of this tilt depends on the photographer'slatitude[5](L), and is equal to90° −L.

Astronomical site testing

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Star trail photographs can be used by astronomers to determine the quality of a location for telescope observations. Star trail observations ofPolarishave been used to measure the quality ofseeingin the atmosphere, and the vibrations in telescope mounting systems.[12]The first recorded suggestion of this technique is from E.S. Skinner's 1931 bookA Manual of Celestial Photography.[13]

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  • Star trails photographed by facing northwest.
  • Star trails over theESO 3.6 m Telescope.[14]
  • A star trail photograph showing the apparent motion of stars around the northcelestial pole;Polarisis the bright star near the pole, just above the jet trail.
  • The constellation ofCassiopeiaover a thunderstorm.[15]
  • Startrail shot in Waterworks Prairie Park, Iowa.
  • Startrail inFayyoum,Egypt.
  • Circumpolar stars in star trails at the La Hague lighthouse, France.
  • Star trails captured during a totallunar eclipse.

References

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  1. ^"All In A Spin".eso.org.Retrieved1 August2016.
  2. ^abISSphotos:
  3. ^"JPL: Photojournal – PIA03613: Meteor Search by Spirit, Sol 643".nasa.gov. December 5, 2005.Archivedfrom the original on January 18, 2006.RetrievedMay 2,2021.
  4. ^Buckley, Drew (2015-04-22)."Star Trails: How to Take Captivating Night Sky Photos".Nature TTL.Retrieved2019-07-14.
  5. ^abcdeMalin, David (2007). "Night-Time and Twilight Photography". In Michael R. Peres (ed.).Focal Encyclopedia of Photography: Digital Imaging, Theory and Applications, History, and Science(4th ed.). Amsterdam:Elsevier.pp. 577–580.
  6. ^abcLandolfi, Larry (February 1996). "Come-as-you-are Astrophotography".Astronomy.24(2): 74–79.Bibcode:1996Ast....24...74K.
  7. ^Burian, Peter K.; Caputo, Robert (1999). "A world of subjects: evening and night". In Kevin Mulroy (ed.).National Geographic photographic field guide: secrets to making great pictures(2nd ed.). Washington, D.C.: National Geographic. p. 276.ISBN079225676X.
  8. ^Manning, Jack (1981-04-05). "Shooting pictures that the eye cannot see".The New York Times.p. ARTS 38.
  9. ^Frost, Lee (2000). "The sky at night".The Complete Guide to Night & Low-Light Photography.New York, New York: Amphoto Books. pp. 156–157.ISBN0817450416.
  10. ^NASA Johnson Space Center (May–June 2012)."ISS Star Trails".NASA JSC Photo Sets on Flickr.
  11. ^abc"PIA03613: Meteor Search by Spirit, Sol 643".Photojournal.NASA. 5 December 2005.Retrieved3 May2021.
  12. ^Harlan, E.A.; Merle F. Walker (August 1965). "A Star-Trail Telescope for Astronomical Site-Testing".Publications of the Astronomical Society of the Pacific.77(457): 246–252.Bibcode:1965PASP...77..246H.doi:10.1086/128210.S2CID122454228.
  13. ^King, Edward Skinner (1931).A Manual of Celestial Photography.Boston, Massachusetts: Eastern Science Supply Co. p. 37.ISBN9780598923523.
  14. ^"Venus Transit Seen Reflected from the Moon".ESO Announcement.Retrieved14 December2012.
  15. ^"The constellation of Cassiopeia over a thunderstorm".eso.org.European Southern Observatory.Retrieved21 March2015.
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