Star trail

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All the stars in the night sky appear to circle the celestial pole (the south pole in this photo). Over a period of several hours, this apparent motion leaves star trails. All In A Spin Star trail.jpg
All the stars in the night sky appear to circle the celestial pole (the south pole in this photo). Over a period of several hours, this apparent motion leaves star trails.
Star trail photographed from Mount Wellington, Tasmania. Aurora australis visible in the background. Star trail and aurora over Mount Wellington, Tasmania.jpg
Star trail photographed from Mount Wellington, Tasmania. Aurora australis visible in the background.
Star trail photography on salt lake in Lut desert in Iran rd strgn dr bybn lwt.jpg
Star trail photography on salt lake in Lut desert in Iran

A star trail is a type of photograph that uses long exposure times to capture diurnal circles , the apparent motion of stars in the night sky due to Earth's rotation. A star-trail photograph shows individual stars as streaks across the image, with longer exposures yielding longer arcs. The term is used for similar photos captured elsewhere, such as on board the International Space Station and on Mars. [2] [3]

Contents

Typical shutter speeds for a star trail range from 15 minutes to several hours, requiring a "Bulb" setting on the camera to open the shutter for 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 professional astronomers to measure the quality of observing locations for major telescopes.

Capture

Video
Star trails photographed from the International Space Station in low Earth orbit at an angle that makes the trails almost vertical instead of circular. International Space Station star trails - JSC2012E039800.jpg
Star trails photographed from the International Space Station in low Earth orbit at an angle that makes the trails almost vertical instead of circular.

Star trail photographs are captured by placing a camera on a tripod, pointing the lens toward the night sky, and allowing the shutter to stay open for a long period of time. [5] Star trails are considered relatively easy for amateur astrophotographers to create. [6] Photographers generally make these images by using a DSLR or Mirrorless camera with 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 allow fast films, such as ISO 200 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 The star trails observed in Eleebana, NSW, Australia on Mar 03, 2019.jpeg
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, the Bulb, or B, exposure setting keeps the shutter open. [9] Another problem that digital cameras encounter is an increase in electronic noise with 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 astronaut Don Pettit recorded star trails with a digital camera from the International Space Station in 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 using imaging software, thus producing the longer exposure." [10] [2]

Star trail images have also been taken on Mars. [11] The Spirit rover produced 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

Star trail over the rocky mountain in Alamut, Qazvin, Iran `khsy z rd strgn dr lmwt qzwyn.jpg
Star trail over the rocky mountain in Alamut, Qazvin, Iran

Star trail photographs are possible because of the rotation of Earth about its axis. The apparent motion of the stars is recorded as mostly curved streaks on the film or detector. [5] For observers in the Northern Hemisphere, aiming the camera northward creates an image with concentric circular arcs centered on the north celestial pole (very near Polaris). [6] For those in the Southern Hemisphere, this same effect is achieved by aiming the camera southward. In this case, the arc streaks are centered on the south celestial pole (near Sigma Octantis). Aiming the camera eastward or westward shows straight streaks on the celestial equator, which is tilted at angle with respect to the horizon. The angular measure of this tilt depends on the photographer's latitude [5] (L), and is equal to 90° − L.

Astronomical site testing

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

Related Research Articles

Diurnal motion is an astronomical term referring to the apparent motion of celestial objects around Earth, or more precisely around the two celestial poles, over the course of one day. It is caused by Earth's rotation around its axis, so almost every star appears to follow a circular arc path, called the diurnal circle, often depicted in star trail photography.

<span class="mw-page-title-main">Astrophotography</span> Imaging of astronomical objects

Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon, Sun, and planets, modern astrophotography has the ability to image objects outside of the visible spectrum of the human eye such as dim stars, nebulae, and galaxies. This is accomplished through long time exposure as both film and digital cameras can accumulate and sum photons over long periods of time or using specialized optical filters which limit the photons to a certain wavelength.

<span class="mw-page-title-main">Shutter speed</span> Length of time when the film or digital sensor inside a camera is exposed to light

In photography, shutter speed or exposure time is the length of time that the film or digital sensor inside the camera is exposed to light when taking a photograph. The amount of light that reaches the film or image sensor is proportional to the exposure time. 1⁄500 of a second will let half as much light in as 1⁄250.

<span class="mw-page-title-main">Exposure (photography)</span> Amount of light captured by a camera

In photography, exposure is the amount of light per unit area reaching a frame of photographic film or the surface of an electronic image sensor. It is determined by shutter speed, lens F-number, and scene luminance. Exposure is measured in units of lux-seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.

<span class="mw-page-title-main">Motion blur</span> Photography artifact from moving objects

Motion blur is the apparent streaking of moving objects in a photograph or a sequence of frames, such as a film or animation. It results when the image being recorded changes during the recording of a single exposure, due to rapid movement or long exposure.

<span class="mw-page-title-main">Observational astronomy</span> Division of astronomy

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

The science of photography is the use of chemistry and physics in all aspects of photography. This applies to the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film in order to take and develop pictures properly.

<span class="mw-page-title-main">Time-lapse photography</span> Film technique where the frame rate is lower than that used to view the sequence

Time-lapse photography is a technique in which the frequency at which film frames are captured is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus lapsing. For example, an image of a scene may be captured at 1 frame per second but then played back at 30 frames per second; the result is an apparent 30 times speed increase. Similarly, film can also be played at a much lower rate than at which it was captured, which slows down an otherwise fast action, as in slow motion or high-speed photography.

<span class="mw-page-title-main">Bulb (photography)</span> Shutter technique on cameras

The Bulb setting on camera shutters is a momentary-action mode that holds shutters open for as long as a photographer depresses the shutter-release button. The Bulb setting is distinct from shutter's Time (T) setting, which is an alternate-action mode where the shutter opens when the shutter-release button is pressed and released once, and closes when the button is actuated again.

<span class="mw-page-title-main">Astrograph</span> Type of telescope

An astrograph is a telescope designed for the sole purpose of astrophotography. Astrographs are mostly used in wide-field astronomical surveys of the sky and for detection of objects such as asteroids, meteors, and comets.

<span class="mw-page-title-main">High-speed photography</span> Photography genre

High-speed photography is the science of taking pictures of very fast phenomena. In 1948, the Society of Motion Picture and Television Engineers (SMPTE) defined high-speed photography as any set of photographs captured by a camera capable of 69 frames per second or greater, and of at least three consecutive frames. High-speed photography can be considered to be the opposite of time-lapse photography.

<span class="mw-page-title-main">FITS Liberator</span> Software program

The ESA/ESO/NASA FITS Liberator is a free software program for processing and editing astronomical science data in the FITS format to reproduce images of the universe. Version 3 and later are standalone programs; earlier versions were plugins for Adobe Photoshop. FITS Liberator is free software released under the BSD-3 license. The engine behind the FITS Liberator is NASA's CFITSIO library.

<span class="mw-page-title-main">Night photography</span>

Night photography refers to the activity of capturing images outdoors at night, between dusk and dawn. Night photographers generally have a choice between using artificial lighting and using a long exposure, exposing the shot for seconds, minutes, or even hours in order to give photosensitive film or an image sensor enough time to capture a desirable image. With the progress of high-speed films, higher-sensitivity digital sensors, wide-aperture lenses, and the ever-greater power of urban lights, night photography is increasingly possible using available light.

<span class="mw-page-title-main">GoTo (telescopes)</span>

In amateur astronomy, "GoTo" refers to a type of telescope mount and related software that can automatically point a telescope at astronomical objects that the user selects. Both axes of a GoTo mount are driven by a motor and controlled by a computer. It may be either a microprocessor-based integrated controller or an external personal computer. This differs from the single-axis semi-automated tracking of a traditional clock-drive equatorial mount.

Zoom burst is a photographic technique, attainable with zoom lenses with a manual zoom ring.

<span class="mw-page-title-main">Barn door tracker</span> Camera mount used for astrophotography

A barn door tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for the observation or photography of astronomical objects. It is a simple alternative to attaching a camera to a motorized equatorial mount.

Polar alignment is the act of aligning the rotational axis of a telescope's equatorial mount or a sundial's gnomon with a celestial pole to parallel Earth's axis.

<span class="mw-page-title-main">Long-exposure photography</span> Photography using a long-duration shutter speed

Long-exposure, time-exposure, or slow-shutter photography involves using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements. Long-exposure photography captures one element that conventional photography does not: an extended period of time.

<span class="mw-page-title-main">Fireworks photography</span>

Fireworks photography is the process of taking photographs of fireworks at night. It is a type of night photography, specifically using available light of the fireworks instead of artificial light. Without using the flash on the camera, the photographer often exposes the image for a period of time, known as long exposure. Brighter fireworks sometimes support shorter exposure times.

References

  1. ↑ "All In A Spin". www.eso.org. Retrieved 1 August 2016.
  2. 1 2 ISS photos:
  3. ↑ "JPL: Photojournal – PIA03613: Meteor Search by Spirit, Sol 643". nasa.gov. December 5, 2005. Archived from the original on January 18, 2006. Retrieved May 2, 2021.
  4. ↑ Buckley, Drew (2015-04-22). "Star Trails: How to Take Captivating Night Sky Photos". Nature TTL. Retrieved 2019-07-14.
  5. 1 2 3 4 5 Malin, 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. 1 2 3 Landolfi, 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. ISBN   079225676X.
  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. ISBN   0817450416.
  10. ↑ NASA Johnson Space Center (May–June 2012). "ISS Star Trails". NASA JSC Photo Sets on Flickr.com.
  11. 1 2 3 "PIA03613: Meteor Search by Spirit, Sol 643". Photojournal. NASA. 5 December 2005. Retrieved 3 May 2021.
  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. S2CID   122454228.
  13. ↑ King, Edward Skinner (1931). A Manual of Celestial Photography. Boston, Massachusetts: Eastern Science Supply Co. p. 37. ISBN   9780598923523.
  14. ↑ "Venus Transit Seen Reflected from the Moon". ESO Announcement. Retrieved 14 December 2012.
  15. ↑ "The constellation of Cassiopeia over a thunderstorm". www.eso.org. European Southern Observatory . Retrieved 21 March 2015.
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