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What am i doing wrong ?


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hi all

a really good friend in the local astronomy society has loaned me his old 'scope to help me learn the sky as i can't afford to buy one myself as yet (i'm unemployed) for which i am extremely grateful icon_biggrin.gif

here is my problem.......

i set up the telescope and north align it (using a compass) as well as making sure it is level.

the declination (i think that's the right term) i have set to 54 degrees which is my lattitude (er, i think that's the right one!).

when i align the 'scope on something (say the moon) and leave it for a few minutes (for a cuppa usually!) after using the slow motion wheel on the equatorial mount (i think thats the RA one!) to find the "target" again it is always to the top of the eyepiece.

what am i doing wrong ?

probably something really simple that i have overlooked !

thanks

Chris

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If I understand you correctly, it sounds like the target is drifting slowly out of the field. I think your problem is that the alignment isn't good enough. The procedure you describe is a rough alignment. You can get it more accurate by using Polaris. There are descriptions on the net. Some involve a "polar scope" which is located within the mount itself. You probably don't have one and it isn't necessary: you just need to make sure that the scope is pointing parallel to the mount's polar axis. Then you adjust that axis (without touching the RA and DEC axes) so that you can see the north celestial pole through the scope. The mount should be level.

Some instructions can be found here: Polar Alignment of your Equatorial Mountpolar - McWiki

and here: FAQ's & How-To's - How to Polar Align Your Equatorial Mount - Model Number: PolarAlign

You will notice that the north celestial pole is actually a short distance away from polaris. For critical work such as photography you'd want to align on the true pole and carry out a procedure known as drift alignment. For your purposes that's over-kill. If the target stays reasonably centered for 10 or 20 minutes then that's good enough.

The terms for the different axes on your mount can be found here: http://www.astronomyhints.com/equatorial.jpg

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I compasses won't be accurate enough and they point to magnetic north, which isn't what you want. You need to conduct the procedure I described if you want accurate tracking. I've never set up an EQ mount in the way you describe so I have no idea how long one would expect the scope to track for using a rough alignment. My hunch, however, is that the results would be pretty variable. Best do it the right way: it's not hard.

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Assuming that the mount is an equitorial then align on Polaris. Polaris is about a degree off of True North whereas a compass is something like 4 or 6 degrees off.

Don't use the moon. The moon is satellite of the earth and does not follow the ecliptic and does not rotate at the "normal" rate. So it is a bad one to use. Basically expect that to never stay central.

From what you say the mount has no motor drive, so yes whatever was in view a few minutes ago will drift out of view.

Is the finder scope (if there is one) aligned to the main scope?

54 North sounds like York or a line horizontally through there, perhaps a bit North.

Actually what is the scope and mount and anything else.

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yes there is no motor drive.

the finder scope is aligned to the main scope (did that first :))

54 north is bridlington for me (well 54.1to be exact)

the scope is an Optus f=700mm d=76mm on an equatorial mount (i assume the one that came with the scope)

gives a good view of jupiter :D

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Ah.. No motor drive. In that case is anything really wrong at all? The object will obviously move out of the field due to the Earth's rotation. Adjusting the RA axis alone should bring it back. If you find you need to adjust both RA and declination then the mount needs to be aligned better.

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Beat me to it on the lack of motor drive and compass points....

If you align to north using a decent compass, use a motor drive, things should stay pretty much central for 10 minutes or so. My compass needs to be clear of everything metal, or it alters it a lot.

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Ah.. No motor drive. In that case is anything really wrong at all? The object will obviously move out of the field due to the Earth's rotation. Adjusting the RA axis alone should bring it back. If you find you need to adjust both RA and declination then the mount needs to be aligned better.

that was my point.

i can move the RA to get it close but it always ends up in the top of the eyepiece.

now that i have a link to a site on how to polar align it it should be better :)

on a side note, it appears that the mount is made of a non magnetic metal, which might be why i got somewhere close, but not exact.

thanks for your replies :D

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for the "latitude i found around 51 - 54 to be abount right (mines set on 53) but that should be fine, remember when moving the litude ajusters take any weights and scope off first as the bolts can snap

if its set at the right lititude use a app or a star map to find the "dec" and "altaz" settings once you have it in the field of view you use the RA axis just to move it (does the mount have any slomo controls)

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for the "latitude i found around 51 - 54 to be abount right (mines set on 53) but that should be fine, remember when moving the litude ajusters take any weights and scope off first as the bolts can snap

if its set at the right lititude use a app or a star map to find the "dec" and "altaz" settings once you have it in the field of view you use the RA axis just to move it (does the mount have any slomo controls)

thanks :)

yep, got a slomo control for the RA

all i need now (other than a job to buy a 'scope of my own!) is some clear skies to put all this good info into action :D

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