polar alignment without polaris

[SnakeyJ]

From my rather short but nicely dark back garden I can't quite line my mount HEQ5 Pro up on polaris - though I can get a fairish stab using a compass (+ local deviation of 1 44 W) and my local lattitude from GoogleEarth. I have pretty good views ENE to WNW, with the exception of a tall birch tree SSE.

The Synscan certainly gets me in the ball park for most targets with a 25mm EP, but is there anything else I can do to hone the alignment down a bit and improve the tracking?

Thanks - Jake

[SnakeyJ]

Might have to get a rope on that birch and shorten in a little when we have the next dark windy night

[VigdisVZ]

I'm no expert, but you should check up drift alignment.

[cosmojaydee]

Drift Alignment is an accurate method of Polar Alignment to align to the Celestial Pole. It can be used for both northern hemisphere polar alignment and southern hemisphere polar alignment, and is usually performed after Rough Polar Alignment.

A rough polar alignment is performed - then refined by pointing at different stars and observing any drift that occurs. The mount is then adjusted according to the direction of the observed drift.

The procedure for the Northern Hemisphere is as follows:

1. Point the telescope at a star due South that is close to declination 0 degrees.
   
2. Rotate the guider CCD or reticule eyepiece in the telescope so that moving the mount in Right Ascension causes the star to follow a crosshair line very accurately. Consider this line to be the ‘horizontal’. If the mount’s tracking is switched off for a few minutes the star should follow this line.
   
3. Position the star exactly on the centre of the cross hairs.
   
4. Leave the mount tracking and note the drift direction of the star away from the crosshair centre.
   
5. While watching the position of the star, put a hand on the front of the scope and push gently either up or down - enough to move the star visibly. Figure out if you need to push UP to re-centre the star or DOWN.
   
6. If you need to push UP, use the azimuth adjustment to rotate the whole mount clockwise (imagine looking at the mount from above). If you had to push DOWN, rotate the mount anti-clockwise. Start with a small rotation to get a sense of how much change the rotation will produce.
   
7. Go back to step 4. Keep repeating steps 4 to 7 until the star does not drift up or down for at least 5 minutes. (Remember, sideways drift is not important).
   
8. Now point the scope at a star low in the West.
   
9. Centre the star perfectly and let the mount track until a drift is observed.
   
10. Put a hand on the front of the scope and give a gentle push. If you have to push the scope UP to re-centre the star, then you must increase the angle that the polar axis makes with the horizontal. If you need to push DOWN then the angle must be reduced. (It is probably wise to figure out which way the adjustment knobs move your mount in daylight before you do the actual drift alignment. It is quite easy to get confused in the dark and go the wrong way.)
    

You should then repeat the whole procedure until no drift is seen for 10-20 minutes.

[cosmojaydee]

Ooops sorry , but you get the drift

[VigdisVZ]

Ooops sorry , but you get the drift

I see what you did there

[SnakeyJ]

Thanks Carl for putting me on the right track & Cosmojaydee for simpler guide.

I did a quick search on drift alignment and found a detailed guide at http://www.astropix.com/HTML/I_ASTROP/TRACKED/POLAR.HTM, but it was confusing the hell out of me (too late and too much wine!). Cosmos guide quote looks pretty straightforward, so will test this out when the skies eventually clear.

Thanks - Jake

[SnakeyJ]

Sorry Cosmo, My brain had unconsciously filtered the pun out!

Anyone got any tips, stories or advice on late night covert topiary or tree felling - though perhaps this deserves a whole thread on its own!

[VigdisVZ]

Tip: Don't get arrested.

[SnakeyJ]

Yeah much appreciated Carl

[cosmojaydee]

Set fire to it and proclaim its a sign from God, the great burning tree of the Isle of Wight,. I will look forward to reading the story in the Enquirer

[SnakeyJ]

Cheers Cosmo, that made me chuckle! And on a second read I can see some merit to the suggestion. At least some grounds for plausible deniability - who can question an act of God? Though residues from common accelerants (petrol, meths) are likely to raise suspicions of a more earthly/local agent.

Unfortunately most of the leaves are down now, so unlikely to simply blow over in the winter gales. I think I'm left with compromise, moving, chemical poisoning, disease (birch die back disease?) or a proper act of god (lightning looking the most favourable of these).

And of course I could always discuss less drastic options like pruning with the neighbors, but its entertaining to explore the theoretical and more extreme possibilities.

[VigdisVZ]

In all seriousness I suggest getting the neighbors hooked on astronomy.

[breezy]

Strip bark from around base of tree , will take a while and you could always blame it on giant beavers, or try vig's approach