Skyglow filters

[Sheap]

Do these work as well as advertised? almost all of the time ive spent observing has been with moderate light polution, would filters such as
http://www.myastroshop.com/products/...asp?id=MAS-229
help to get better detail out of objects?
Also, do you need a filter selector to use filters? or would that filter fit into my eyepiece?
my eyepieces are basically in 2 parts, theres a metal barrel that can be unscrewed, and a black bit with all the optics in it, am i correct in thinking that the filter would go in between these?

[RAJAH235]

Hiya Sheap. No. The filter screws into the 'shiny bit', errr, barrell. No need to remove it.. in fact, I nip mine up fairly tight.
Filters are avail for light polluted skies, eg; Broadband. They cut the Sodium & Mercury vapour lights which is most of our problem.
But see here for a bit more info... L.

[davemac4091]

Here's an easy one for you experiened and knowledgable guys and gals!?!

Looking out the back balcony this last week and I get to enjoy a fullish moon rise from the eastern sky - what a sight. From one night to the next, I look at IceInSpace to find out when it's going to happen each night. Since I've been doing that, I've noticed something I've never noticed before . . .

The moon doesn't cut the horizon at near the same place from one night to the next!? Earlier this week I took note of where it rose from the horizon (buildings for me); and the next night it rose from a different place. If I placed my hand outwards towards the horizon, with palm facing outwards, there was a width of four fingers between where it rose one night and where it rose to the next!!

I'd always thought that the moon and the planets were on the same plane, (except Neptune?) and that the Moon would behave like the sun does; that is, over the space of a year the arc of the sun would oscillate between 12.5 deg either side of the equator, and hence, from Sydney, it would rise from near the same place each day.

Does the sun do this too? Or is it only the moon? To paraphrase an old bloke on TV, "Why is it so?" Is it an elliptical orbit, or some other reason?

[OneOfOne (Trevor)]

I think the main reason it appears to rise at different spots each evening is because it is around 50 minutes later each time? The orbit appears at an angle to our horizon and so when it rises, it will appear to have moved around a bit.

This is probably easier to check when setting because it will be easier to grasp the concept. I expect if you watch where it sets one night and the next day note where it is about the same time as it set the previous day, and drop a line straight down to the horizon, it should be the same place? Well, that's my theory. The Sun does a similar thing, but the time difference is only 2 minutes (roughly) and so the difference is pretty small, making it appear to "walk around the horizon" during the year.

[OneOfOne (Trevor)]

I just received my Badder UHC-S filter and was out last night and swung the scope around to Eta Car, which was getting pretty low in the sky and put in the 10mm. I could make out some of cloud formation, but not a lot. I had to point in the general direction of my neighbour who had just turned on his outdoor spotlight, so it wasn't exactly the best time to try to see much. I put the UHC filter on the eyepiece and tried again. The sky went MUCH darker and the whole area became much easier to see, the cloud was plainly obvious now whereas previously, without the filter, you had to concentrate to see anything.

So if you have to view from less than dark sites, a filter may be a good investment to at least allow you to see things you won't be able to see otherwise...not easily at least. I didn't try the OIII, probably should have to see the comparison.

[rmcpb (Rob)]

Light polluted sites are a problem and we often go to the extent, and expense, of buying filters then never giving them a chance. To be of any real benefit, other than dimming the image and making the background blacker, your eye has to be dark adapted otherwise it is just not sensitive enough to utilise the light coming through the lense. Soooooooooooooo in a light polluted area try:

• Using an eyepatch over your observing eye when not at the eyepiece to preserve dark adaption. Looks silly but who is going to see you
• Making an observing hood that goes over your head and eyepiece for use when you are at the eyepiece and put the eyepatch on BEFORE taking the hood off.
• Making a tube extension/dew shield to cut the amount of off axis light entering your eyepiece and reducing contrast.
• If you suffer from a point source of light pollution make a panel out of electrical conduit and a tarp to block this light off.
• Don't try to observe below 45 degrees above the horizon to cut down the amount of air you look through.

Often, if the light pollution is not too bad these steps and a broadband filter are enough. Afterall light pollution does to your eyes what walking into a lit room kills your night vision.

Enough rambling, give 'em a go.