Couple of Stellarium questions....

[ScubaMike]

Folks,

Couple of questions, the answers to which I have not been able to find on the forum:-

1. Light pollution setting. Is there an online resource which will give me this? Or do I visually observe, and adjust the setting to match my general conditions?

2. RA/DEC. Once I have polar aligned, I swing OTA to a known star, click on that star in Stellarium. What are the readings I should be moving my setting circles to? There are 4 listed:-

RA/DE (j2000)

RA/DE (of date) (I think this is the correct one)

Hour Angle/DE (geometric)

Hour Angle (apparent)

Out of interest, should I use Polaris as a star by which to set my cicrles, or something closer to the horizon?

[Nova]

I do the light pollution visually but have always wondered if there is an online resource. TBH I dont use this setting much and tend to turn LP right down and just use stellarium to find things. If I cant see it in my scope then I know there is to much LP and move on to something else

and yes set to RA/DEC of date. Im not to sure what the J2000 is but it is constantly changing which makes it difficult (impossible?) to use. I never use polaris to callibrate my RA. If you correctly polar align your mount its pretty hard to align your scope on it. At this time of year i calibrate on Arctaurus or Vega but any bright star that you know and can easily recognise will work fine. If im being really fussy I will callibrate on one and then turn the scope to the other just to check. The circles on my mount are not very accurate but close enough and have managed to use them succesfully in the past

[ScubaMike]

Thanks Steve,

Nice to have confirmation as I'm still fumbling around.

Arcturus & Vega are both nicely visible (when the damn clouds part) so will probably set on one, and try to confirm by using circles to "target" the other, and check to see what my error is.

[Nova]

yep thats it. dont be surprised if when you check its not spot on. Not sure how accurate the EQ5 circles are. But it will certainly give you a guide to finding DSO's A good method I have found is to callibrate your RA circle then turn your scope to the RA of the object you want to find and let it track so you know that the scope will hold the same RA. Then release your dec motor and manually sweep the dec accross the sky using the slow mo cable. I managed to find M13 pretty easily doing this and will be trying it on other targets. Fingers crossed for clear skys too!! Seems like an age since I was last out

[Vali x]

thanks guys, good info for me too !!

[umadog]

The light-pollution scale in stellarium goes from 1 to 8. The scale on the world light pollution map also has 8 levels (e.g. ClearDarkSky Light Pollution Map). I don't know if this correspondence is by accident or design. I do know, however, that if I set the LP level based on the map colours stuff looks about right.

[Nova]

thanks umadog, good to know I shall have to have a play with that

[Daggerstab]

1. Light pollution setting. Is there an online resource which will give me this? Or do I visually observe, and adjust the setting to match my general conditions?

The light pollution setting in Stellarium is based on the Bortle scale:

Bortle Dark-Sky Scale - Wikipedia, the free encyclopedia

(there's a table there with example objects)