Last updated: 26 June 2002

Terrestrial and Astronomical.. when and why

Sent:	Friday, June 21, 2002 21:40:36
From: (Richard Seymour)
Along the years there have been a number of questions along the lines 
of: "Why is (isn't) the scope in Astronomical (Terrestrial) Mode?"
Some people have been bothered by seeing "Setup > Targets" be
in Terrestrial mode before they've gotten around to aligning.

Let's see if we can clear this up:

Many folks don't realize when Terrestrial and Astronomical kick in
 and out.  They usually so do quite reasonably, and pretty much allow
you to almost forget about their existence.  In short: don't worry
about them, let the scope automagically choose for you.

In the following, the terms "sidereal" and "astronomical" mean the 
same thing.  I'll usualy say "sidereal" when i want you to think/
remember that the star-tracking motors are turning.

When you first power up, and if you -abort- the alignment sequence,
 the sidereal drive doesn't start.

So you're in "Terrestrial" mode.  Fine.

You can start the sidereal drive in many ways:
(a) GoTo any Astronomical object.  Star, Planet, Comet, Galaxy.
  At the end of the slewing, the sidereal drive will start.
(b) GoTo a specific RA/Dec.   The sidereal drive will start.
(c) do an alignment (one, two, easy or auto)... since the last 
 step of that -is- a "GoTo an astronomical object", sidereal starts.
(d) Setup > Targets > Astronomical [enter]   starts it.

(the LXD55 group has discovered a really weird sequence i haven't
tried yet on the other scopes.. so i won't list it).

How/when would you want to -not- be in Astronomical (sidereal tracking)
If you're pointing at Landmarks, or waiting for a Satellite to appear.
The ways to get -there- are:
(e) GoTo a Landmark.  Doing so kills sidereal, you're Terrestrial.
(f) Press [GoTo] after predicting a satellite pass.. the scope will
 slew (first to where you'll -lose- the satellite, then to where
 you'll pick it up), and wait quietly, not moving.
 **After** the pass, (ended by holding MODE for 4 seconds, or simply
 by reaching the end of the pass), the telescope will revert to 
 whichever mode was in force before you pressed the [goto] at the
 beginning of this paragraph.  Sidereal or Terri.
(g) GoTo an Alt/Az coordinate set.
(h)  Setup > Targets > Terrestrial [enter].
and (by inference)
(i) it's there from power-on, until you do one of (a) thru (d) above.

So that's it... don't worry that it's not "Astronomical" upon power-up,
it'll become Astronomical by your first GoTo.

footnotes: if you do NOT start your sessions with a GoTo, and/or if
you power up after a PARK, so it doesn't need to do an Align, then, 
indeed, your sidereal drive will -not- self-start.  I always work-around
that by GoTo'ing something near where i might otherwise manually slew..
that startts the drive, and has the secondary benefit of showing me
how well GoTo's are going that evening.
Some -older- versions of the Autostar firmware (early 2.0 range) did
NOT always switch modes properly... Comets would not start Sidereal,
for example, and GoTo Landmarks did not always turn it off.

have fun

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