![[NASA/STScI/AURA] Gaseous streamers flutter in stellar breeze](2002-07-05-n44c-nebula.jpg)
Q: When NASA and astronomers photograph celestial bodies, how do they decide which way to orient
the camera and images? In space there is no up or down nor any anchor orientation point (i.e.,
north/south). Ben R., Buffalo, New YorkCopyright 2002, all rights reserved
"Up" is north for star photos
Q: When NASA and astronomers photograph celestial bodies, how do they decide which way to orient
the camera and images? In space there is no up or down nor any anchor orientation point (i.e.,
north/south). Ben R., Buffalo, New York
A: Astronomers use several geometries where "up" is not our north. Space, certainly, has no intrinsic north as you say.
[NASA/STScI/AURA] Gaseous streamers flutter in stellar breeze
"In studying galaxies, a galactic coordinate system with the plane of the Milky Way defining the equator is used," says Anthony Cook of Griffith Observatory in Los Angeles.
However, the most widely used astronomical coordinate system is the Equatorial System. Up is our north. The reference plane is our equator.
We earthlings take celestial pictures with cameras on Earth or from spacecraft and space stations in the neighborhood. Since our Earth is spinning, the stars appear to sweep around us.
Because of Earth's rotation, a star appears to slip out of the telescope view, unless the telescope tracks the star. Similarly, our closest star, the Sun, appears to move across the sky during the day.
Before the late 1960s, astronomers tracked stars by carefully rotating a mechanical tracking bolt, mounted to the telescope. They took the picture when the object was close to due south. That put south at the top of the photograph.
As spacecraft returned images of the Earth, Moon, and planets, this convention eroded, says Cook.
Now, computer programs keep the telescope on target during a long exposure. The program also records the orientation of the picture frame with respect to north. Observatories specify the orientation of each image.
Note: The figure shows the computer-generated orientation of a 1996 picture taken using Hubble's Wide Field Planetary Camera 2.
(Answered Jul. 5, 2002)
Further Surfing:
NASA: N44C nebula, more info about the nebula
Jim Pennington: Astrophotography primer
The Astronomical Companion by Guy Ottewell, Universal Workshop, 2000