Using a GEM for alt-az setting - how?

This is probably obvious but I can't figure it out.

I want to take some pictures of iridium flares, just for fun.
Maybe 2 minutes exposures to get some of the background stars too.
I also want to set up my equatorial mount and camera, pointing at the
correct alt-az well in advance (daytime).

Assumed starting settings;
Mount is set up well polar aligned.
RA is at zero deg. By this I mean the counter weight bar is pointing due
north. DEC is pointing due up/north.
I now set the setting circles to RA=0 and DEC=90.

How can I now convert the alt/az values I get from heavens-above so that I
can preset my mount to them using my setting circles? I strongly feel this
should be possible but may of course be wrong...

I'm using Linux and have Cartes du Ciel, Kstars, Celestia, and Stellarium
installed. They have some convert tools but I obviously can't use them or
they are not intended for this task.

All help and/or pointers much appreciated

I'm at app. 62 deg. north and 17 deg. east.

And Happy Easter to all...

This is probably obvious but I can't figure it out.

I want to take some pictures of iridium flares, just for fun.
Maybe 2 minutes exposures to get some of the background stars too.
I also want to set up my equatorial mount and camera, pointing at the
correct alt-az well in advance (daytime).

Assumed starting settings;
Mount is set up well polar aligned.
RA is at zero deg. By this I mean the counter weight bar is pointing due
north. DEC is pointing due up/north.
I now set the setting circles to RA=0 and DEC=90.

How can I now convert the alt/az values I get from heavens-above so that
I
can preset my mount to them using my setting circles? I strongly feel
this
should be possible but may of course be wrong...

I'm using Linux and have Cartes du Ciel, Kstars, Celestia, and
Stellarium
installed. They have some convert tools but I obviously can't use them
or
they are not intended for this task.

All help and/or pointers much appreciated

I'm at app. 62 deg. north and 17 deg. east.

And Happy Easter to all...
http://home.att.net/~srschmitt/celestial2horizon.html
http://www.seds.org/~spider/spider/S....html#ecliptic
The conversion depends on time as well as location, which makes it
somewhat harder.
For an 'off the shelf' solution:
http://www.softpedia.com/get/Others/...n/Altair.shtml


Best Wishes

On Apr 6, 7:57 am, Iordani wrote:
This is probably obvious but I can't figure it out.

I want to take some pictures of iridium flares, just for fun.
Maybe 2 minutes exposures to get some of the background stars too.
I also want to set up my equatorial mount and camera, pointing at the
correct alt-az well in advance (daytime).

Assumed starting settings;
Mount is set up well polar aligned.
RA is at zero deg. By this I mean the counter weight bar is pointing due
north. DEC is pointing due up/north.
I now set the setting circles to RA=0 and DEC=90.

How can I now convert the alt/az values I get from heavens-above so that I
can preset my mount to them using my setting circles? I strongly feel this
should be possible but may of course be wrong...

I'm using Linux and have Cartes du Ciel, Kstars, Celestia, and Stellarium
installed. They have some convert tools but I obviously can't use them or
they are not intended for this task.

All help and/or pointers much appreciated

I'm at app. 62 deg. north and 17 deg. east.

And Happy Easter to all..
..
Iordani

It woud be easier (mabye) to do a Pole sighting then
drop the *Polar Axis* so that the OTA is parallel with
the ground. (Use a level to check it.)

The declination then becomes the azimuth.
Then set the RA circle to 0.0 and that becomes
your altitude. Of course you will have to multiply
all the RA setting by 15 to get the correct
altitude but you can take a pocket calculator
with you to your setup point.

Ben

Ben wrote:


It woud be easier (mabye) to do a Pole sighting then
drop the *Polar Axis* so that the OTA is parallel with
the ground. (Use a level to check it.)

The declination then becomes the azimuth.
Then set the RA circle to 0.0 and that becomes
your altitude. Of course you will have to multiply
all the RA setting by 15 to get the correct
altitude but you can take a pocket calculator
with you to your setup point.

Thanks Ben, I am aware of this but don't want to do it since this will mess
up my polar alignment each time. This is also why I feel it should be
possible if the proper conversion was applied.

In uk.sci.astronomy message , Fri, 6
Apr 2007 14:57:11, Iordani posted:

This is probably obvious but I can't figure it out.

I want to take some pictures of iridium flares, just for fun.
Maybe 2 minutes exposures to get some of the background stars too.
I also want to set up my equatorial mount and camera, pointing at the
correct alt-az well in advance (daytime).

To get substantially the whole of a bright flare, you will need a field
of view of a couple of degrees or more, and therefore your pointing will
not need to be very precise.

Why not, in the daytime, set up a light pole at the required azimuth,
with a marker at the right height (remembering to allow for the height
of the scope and any slope of the ground), set the scope to point to the
marker, and note the settings needed? With a light or reflector as a
marker, you could do that at night too.

--
(c) John Stockton, Surrey, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Thanks Ben, I am aware of this but don't want to do it since this will mess
up my polar alignment each time. This is also why I feel it should be
possible if the proper conversion was applied.

Iordani,

Don't know what I was thinking - that method won't work
near the Pole any way.

The solution is in Chapter 13 of Meeus' Astronomical
Algorithms and requires that you compute *apparent
sidereal time*. This can be done on an ordinary scientific
calculator but it requires a little practice.

Regards

Ben

Later,

Now if you are getting the alt/az coords from a URL
then the sidereal time doesn't come into question since
the observation time and positions are given.
So:
tan H = hour angle (RA)
A= azimuth
phi = your latitude
h = altitude
d = declination

Then:

tanH = sinA / cosA sin phi - tan h cos phi

This is if you reckon North as 0 deg. If you reckon from
the South then *add* sin phi to tan h in the denominator.

for declination:

sin d = sin phi sin h + cos phi cos h cos A

But if you measure from the South *subtract*
sin h - cos phi

Hope this helps.

Ben

Thank you Ben.
I will try this out.
If you where to put some parenthesis into your calculations for tanH, where
would they be? I have suggested some below, is this correct?

Then:

tanH = sinA / cosA sin phi - tan h cos phi
tanH = (sinA / (cosA sin phi)) - (tan h cos phi)

Roger Hamlett wrote:


http://home.att.net/~srschmitt/celestial2horizon.html
http://www.seds.org/~spider/spider/S....html#ecliptic
The conversion depends on time as well as location, which makes it
somewhat harder.
For an 'off the shelf' solution:
http://www.softpedia.com/get/Others/...n/Altair.shtml

Thank you, I will have a look at these sites.

Dr J R Stockton wrote:


To get substantially the whole of a bright flare, you will need a field
of view of a couple of degrees or more, and therefore your pointing will
not need to be very precise.

Why not, in the daytime, set up a light pole at the required azimuth,
with a marker at the right height (remembering to allow for the height
of the scope and any slope of the ground), set the scope to point to the
marker, and note the settings needed? With a light or reflector as a
marker, you could do that at night too.

Thanks.
I have done it along these lines with some success, but sometimes I still
miss the 'target'. I thought it would be fun to do it
more 'scientifically' and learn something new.