Altazimuth vs. equatorial?

Question

I plane words, what's the difference between these two kind of telescopes?

Answer 1

Altazimuth mounts move in two directions:
Up and down (north and south), and side- to- side (east and west).
Equatorial mounts are much better suited to sky viewing, because the mount's motion can be made to follow the apparent motion of objects in the sky (compensating for the Earth's rotation).
The difference isn't in the telescopes, it's in the telescope mounts.

Answer 2

If all you are doing is visual observation, computer controlled versions of both will be mostly equivalent. But if you want to do astrophotography with a small telescope, your logical choice is an equatorial mount because the altazimuth mount will lead to a rotation of the field of view, for which you would need yet another correction rotor... what a pain!

OTOH, if you have a 15m telescope, you don't get a choice because one can not practically build equatorial mounts for those large mirrors. The field rotator on the focal plane array of such an instrument is only a small addition to the already complex mechanical and optical system.

Answer 3

Amansscientiae is correct.

Really the only benefit on a "smaller" telescope is that it allows you to take extremely long exposure times for astrophotography.

The only benefit for an alt-azm mount is that it requires less setup for viewing. To control it, you can simply set it up and view/control it without any problem.

For an equatorial mount, you have to at least be able to find Polaris (The North Star), and be able to aim the telescope at it, and orient the mount in a specific manner; only then will it be easy (easier?) to track objects. For more accuracy with the equatorial, you actually have to aim at the "Celestial pole" which is ~0.7° away from Polaris.

Personally for beginners I recommend the equatorial mounts, because it helps develop a better understanding of how the sky moves. Here are some links to the things I was talking about, and the last two are from the Saint Louis Astronomical Society about how to get stared in astronomy (the last one is a PDF). Enjoy!

http://www.memphisastro.org/Mounts.html

http://en.wikipedia.org/wiki/Polaris

http://en.wikipedia.org/wiki/Celestial_pole

http://www.slasonline.org/resources.htm

http://www.slasonline.org/resources_handout_07KMM.pdf

Answer 4

The above is correct. An altaz mount moves the telescope up and down or right and left. An equatorial mount is basically an altaz mount tipped so that one axis is parallel to the Earth's axis of rotation. That axis is called the polar axis. Then the telescope can follow the stars as they rise and set by turning only around the polar axis. The other axis, called the declination axis, never has to move to keep a star in the field of view. In contrast, an altaz mount has to make complicated motions, going mostly up as the star rises, then turning sideways as it passes overhead, then going down as it sets. Modern computer controls can drive both the alt and az motors is varying speeds to simulate the motions of an equatorial mount though, so computer controlled altaz mounts are beginning to be more popular than equatorial mounts, who's motions can seem clumsy and confusing when used manually.

Answer 5

Wow! Amans....

I could only DREAM of owning a 15m telescope. Can I come visit you?