beginner's equatorial mount question

OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!

Thanks.

On Sun, 10 Oct 2004 23:24:20 GMT, anon wrote:

OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!

I don't fully see your problem - which is probably why you have a
problem ;-)

Imagine a mounting like a normal tripod mount. Once that can pivot
around a vertical axis - left and right (azimuth) - and up and down
(altitude).

Ok, now imagine mounting a stick on the tripod head. Point the stick
at the horizon (altitude = 0 degrees) and twist it left to right. It
follows the horizon line.

Now point it down towards the ground and spin it from left to right.
This time the stick traces an arc.

If you take an alt-az mount (like the tripod) and tilt it so that the
vertical axis point to the north celestial pole - voila, you have an
equatorial mount. Objects to the south of you are viewed by pointing
the scope 'down' like the stick.

Your statement that the telescope just traces an arc from east to west
via north, for southerly objects, is true. However, the northward
motion is in your local co-ordinates (altitude) not declination. The
telescope points at the same declination as you slew it from left to
right (right ascenscion).

There's no particular magic here and you may be getting confused by
thinking about it too hard (happens to us all). Alternatively, I may
be getting confused and not reading your problem properly ;-)


--
Pete Lawrence
http://www.digitalsky.org.uk

This helped me ......
http://www.astronomyboy.com/eq/

Regards
Mark


"Pete Lawrence" wrote in message
...
On Sun, 10 Oct 2004 23:24:20 GMT, anon wrote:

OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!

I don't fully see your problem - which is probably why you have a
problem ;-)

Imagine a mounting like a normal tripod mount. Once that can pivot
around a vertical axis - left and right (azimuth) - and up and down
(altitude).

Ok, now imagine mounting a stick on the tripod head. Point the stick
at the horizon (altitude = 0 degrees) and twist it left to right. It
follows the horizon line.

Now point it down towards the ground and spin it from left to right.
This time the stick traces an arc.

If you take an alt-az mount (like the tripod) and tilt it so that the
vertical axis point to the north celestial pole - voila, you have an
equatorial mount. Objects to the south of you are viewed by pointing
the scope 'down' like the stick.

Your statement that the telescope just traces an arc from east to west
via north, for southerly objects, is true. However, the northward
motion is in your local co-ordinates (altitude) not declination. The
telescope points at the same declination as you slew it from left to
right (right ascenscion).

There's no particular magic here and you may be getting confused by
thinking about it too hard (happens to us all). Alternatively, I may
be getting confused and not reading your problem properly ;-)


--
Pete Lawrence
http://www.digitalsky.org.uk

"anon" wrote in message
...
OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!


Pete gave a real reply, I'll do a quick and dirty one. To point south,
basically rotate the tube through 90 degrees left or right. Rotate it on the
axis 90* to the tube, the declination axis. Now rotate the RA axis 90
degrees and you should be pointing south. Kinda.

On Mon, 11 Oct 2004 16:08:35 +0100, "mutt"
wrote:

This helped me ......
http://www.astronomyboy.com/eq/

A picture (or animation) says a thousand words ;-)

The animation of the telescope looking due south is interesting
though. The scope ends up looking at the place in the sky where the
observer's meridian (zenith -- south point on the horizon) cuts the
celestial equator. Technically, I suppose that any point from the
zenith to the observer's horizon (along the meridian line) is pointing
south.


--
Pete Lawrence
http://www.digitalsky.org.uk

On Sun, 10 Oct 2004 23:24:20 GMT, in uk.sci.astronomy , anon wrote:

OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

Er, no. An equatorial mount has two rotation axes, just the same as an
alt-az mount does. So it can scan the entire sky in just the same way.
Consider it as simply an alt-az mount with the base tilted.

What it /does/ do that an Alt-az mount can't, is that you can move it in
only one axis, and track objects in the sky.

--
Mark McIntyre
CLC FAQ http://www.eskimo.com/~scs/C-faq/top.html
CLC readme: http://www.ungerhu.com/jxh/clc.welcome.txt

Thanks for all the responses. In the wee hours of this morning (I'm
turning nocturnal) I found this explanation too:
http://www.skywatchertelescope.com/D...s/Pointing.pdf

I spent some time this evening fiddling in the privacy of my garage. I
think I've got the hang of it now. Was frustrated last night 'cos
friend came round to have a peek and I got all tangled up in the
scope. Not very impressive for him.

TTFN

anon wrote:
OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!

Thanks.

Hi,

Like this
http://arnholm.org/astro/observatory/obs_pillar_c8.jpg

Northern hemisphere (60N)
Polar aligned Vixen GPDX
Telescope pointing south

Clear skies
Carsten A. Arnholm
http://arnholm.org/

On Tue, 19 Oct 2004 17:16:15 +0200, "Carsten A. Arnholm"
wrote:

anon wrote:
OK, my brain hurts

Given a polar-aligned equatorial mount in the northern hemisphere, how
does one view objects located south of one's position? Surely the
telescope just traces an arc from east to west via north?

I know this is fundamental stuff, but can someone please point me to
some pictures?!

Thanks.

Hi,

Like this
http://arnholm.org/astro/observatory/obs_pillar_c8.jpg

Northern hemisphere (60N)
Polar aligned Vixen GPDX
Telescope pointing south

Clear skies
Carsten A. Arnholm
http://arnholm.org/


Thanks Carsten et.al. Think I've finally got it sussed. Since my mount
is undriven, and undrivable, I'm thinking of converting to a simple
DIY Dob' mount until budget permits a drivable EQ mount.