Some basic questions

John Smith wrote:

I have some questions which I hope the community at large can help me
answer:

Others have answered most of them pretty well, I think.

snip

3. I see fantastic telescopes with lots of gadgetries in Sky & Telescope.
I can do ray tracing for a theoretical Newtonian or Cassegrain (learned that
in high school). However, what are those short stubby gleaming telescopes
with coiled cables and a keypad? There are lots of advertisements on these,
so I assume that many people must own them. Maybe because they are so
common, the advertising copy is, so as not to offend the majority,
deliberately snobbish to leave out any clues on how they work or what they
are supposed to do.


The "short stubby" part implies 'folded' optics, as in the
Schmidt-Cassegrain and Maksutov designs others mentioned; their tubes
are about half as long as is required by a Newtonian of the same
focal length. What I'd like to add is that the "cables and a keypad"
most likely belong to computerized drive controllers, often
collectively referred to as "GoTo" systems although each manufacturer
has its own brand name. At a minimum these will automatically point
the 'scope toward whatever point in the sky whose celestial
coördinates are entered on the keypad (which usually includes 'arrow
keys' for manual adjustment as well, replacing the fiddly knobs of
conventional mounts). More advanced models include databases of
thousands of objects, allowing one to enter a name or catalogue
number instead of RA and Dec.; automatic alignment systems, which --
once calibrated at the beginning of a session by pointing the 'scope
at two or three bright stars -- let the tracking system orient itself
to the sky regardless of its physical position; and GPS receivers,
which tell the controller its geographic location and the exact time,
so the observer doesn't have to bother with these details either.
Note that many of these systems are based on altazimuth mounts: the
computer's ability to convert from celestial to horizon coördinates
and back makes a more complex and expensive equatorial mount
unnecessary -- for visual use at least.

--
Odysseus