Can a single picture sum up all of 2010? In a way, yes. The above multiple-exposure photo shows the figure-eight path of the sun over the course of the entire year, known as an analemma.
Analemma photographs are made by taking a picture of the sun from the same place at the same time of day once or twice a week, generating 30 to 50 frames. This picture, made in Veszprem, Hungary, combines 36 photos of the sun taken at 10 a.m. local time between January and December. A separate picture of the neighborhood taken from the same location but at a different time of day was digitally composited into the foreground.
The sun makes this shape over a year because Earth rotates on a slightly different axis than the sun, and our planet also travels on an elliptical orbit. As one hemisphere of Earth tilts farther from the sun, the arc of the sun's daily path seen from that location lowers toward the horizon. The sun's arc then gets higher in the sky as the tilt reverses. The sun's highest point in the sky, seen in this analemma, occurs during the summer solstice, while its lowest point is during winter solstice. (Find out about a lunar eclipse that happened on the 2010 winter solstice.)
Because of the time and precision involved, photographs of analemmas can be very difficult to produce. So far, only about 20 people worldwide have released successful analemma photos, according to Babak Tafreshi, founder of the astrophotography website The World at Night (TWAN).
The sun seems to rise from behind the hills near the Tholos, a circular building in the sanctuary of Athena Pronaia in ancient Delphi, in an analemma photo composite made in Greece in 2001.
"In the classic way, all analemmas were made on single frames of film using multi-exposure settings and placing a camera on a fixed platform," TWAN's Tafreshi said in an email. "Newer analemmas are generally made by placing the digital camera on that fixed platform and shooting a single image each time and composing all the frames later."
It's possible to make a classic analemma that includes the pictures of the sun and the foreground on the same piece of film—but that's risky business, according to Tafreshi. For starters, safely taking pictures of the sun requires a special solar filter on the camera.
To also capture the Earthly landscape, "the photographer needs to make an exposure without a solar filter in day time (and usually when the sun is not in the view), and having this overexposed or underexposed will ruin the year-long work," he said.
One disk of the sun shines like a pendant on a celestial necklace in the first known analemma photo to feature a total solar eclipse. The composite picture includes an exposure of the eclipsed sun as it appeared over Antalya, Turkey, in March 2006. The rest of the analemma shows the sun's path over Bursa, 311 miles (500 kilometers) north, between July 2005 and July 2006. (Find out more about how this analemma was constructed.)
During a solar eclipse, the moon passes between Earth and the sun, blocking most of the sun's light. All that's visible during totality is the sun's relatively faint upper atmosphere, called the corona.
The eclipsed sun appears brighter in this analemma because the shot was taken without a solar filter and for a longer exposure time, allowing the photographer to capture the corona and the darkened landscape of Antalya, seen in the foreground. (Also see the March 2006 solar eclipse as viewed from space.)
This analemma photo-composite shows the sun's path as it appeared over Girona, Spain, from March 2003 to March 2004. After capturing 53 disks, one every seven days at 9:15 a.m. UT, photographer Juan Carlos Casado then added a foreground picture of the Cap de Creus (Cape of Crosses) National Park, in the easternmost part of the Iberian Peninsula (map).
Although analemmas traditionally depict the path of the sun, it's also possible to make an analemma of the moon (picture). Due to the moon's titled and elliptical orbit around Earth, the moon seems to return to the same place in the sky 51 minutes later each day, on average. That means taking pictures 51 minutes later each day for a lunar month produces a similar figure eight in the sky.
Analemmas may also appear for observers on the surfaces of other planets, based on orbital calculations, but for some worlds the shape of the sun's path wouldn't trace a figure eight. On Mercury, for example, the interplay between axial tilt and orbital path would make an analemma that's a nearly straight line from east to west. On Mars, meanwhile, the analemma would look more like a teardrop. (See an illustration of a Mars analemma.)
The first analemma photograph ever made—created over New England in the U.S. between 1978 and 1979—stands as one of the few analemma pictures in the world that does not use a composited foreground. The shot includes 44 exposures of the sun and a picture of a house, all taken from the same location and all on a single frame of film.
In addition, during summer solstice, winter solstice, and one of the equinoxes, photographer Dennis di Cicco made long exposures with a solar filter, beginning each day at sunrise and ending at 8:30 a.m. ET. The resulting image shows part of the sun's arc during those three days.
"Most people say you have to be nuts to attempt a year-long exposure of the sun," di Cicco wrote on the TWAN astrophotography website. "Those who have succeeded will probably agree!"