Sharing tips and techniques to help amateur astronomers get the most out of light polluted skies.

UltraBlock and Small Scopes

Orion UltraBlock filter, 1.25 inchIf you peruse posts on Cloudy Nights and other forums on the web, you’ll find claims that narrowband filters don’t work well with small scopes, that you need at least 8 inches (or 10 inches, or 12 inches…) of aperture to get any benefit from them. I’ve never agreed, having used the UltraBlock to advantage with my 4.25 inch (108mm) Newtonian to see through local light pollution.

4.25 inch (108mm) Newtonian reflectionRecently, I put this hypothesis to the test with my 4.25 inch (108mm) Newtonian on a night with particularly bad haze and light pollution. It was a night on which 3rd magnitude stars were hard to see. I found that planetary nebulas which were invisible in the 4.25 inch showed up relatively clearly using the UltraBlock. So as far as I can tell, you can use the UltraBlock filter to help you see through light pollution just as effectively with small apertures as with large. Here are the details….


Star Clusters

 NGC 884 and NGC 869Star clusters, both open and globular, generally show up well in washed-out skies. There are lots of relatively bright clusters, and their stellar nature allows you to use magnification to darken the background and enhance the contrast. YGlobular cluster M3ou won’t catch quite as many stars as you would in dark skies, but there is still plenty to see: clusters that look spectacular in dark skies still look quite stunning even with light pollution. The brighter globular clusters do particularly well in washed-out skies.



Orion UltraBlock Filter

 Orion UltraBlock filter, 2 inch version with 1.25 inch version seen behind itThe Orion UltraBlock is a narrowband filter intended to improve the contrast on emission nebulas. It does this by letting through the hydrogen-beta and ionized oxygen light frequencies common to emission nebulas and blocking other light frequencies, including most common sources of light pollution. The UltraBlock filter gets good reviews on Cloudy Nights, but there are often comments on the forums that while it works well in dark skies, it doesn’t perform so well with heavy light pollution.

 I’ve found the UltraBlock to be very effective in my light polluted skies. It helps me both see more details in objects that are already visible and pull out objects that otherwise I couldn’t see at all. It works particularly well with planetary nebulas. Orion’s UltraBlock gets two thumbs up from me as a light pollution fighter. Let me explain why…


3C 273: Quasars are Easy

Q: How powerful is your telescope?

A: It’s powerful enough that even with this light pollution I can see things 2.5 billion light years away, or nearly a fifth of the way back to the Big Bang.

3C 273 was the first quasar identified and it is bright enough to be seen in many amateur telescopes. Because quasars are star-like (the term quasar was coined as an abbreviation for quasi-stellar radio sources), they show up well in washed-out skies if you use magnification to darken the background. At magnitude 12.8, under typical urban/suburban light pollution 3C 273 should be visible in 8 inch (200 mm) telescopes on nights with good transparency, but it can be very challenging for 6 inch (150 mm) telescopes on all but the most transparent nights.

At 2.44 giga light years (750 megaparsecs or 1.5 x 1022 miles), 3C 273 is hands-down the farthest object brighter than 13th magnitude. While it looks no different than an ordinary star, just think how long that light took to get to you: the photons hitting your eye started their journey during the Proterozoic eon, just before Earth’s first major ice age (the Makganyene ice age), and about the time that the first generations of photosynthetic life forms triggered the Oxygen Catastrophe. Way cool!

Now, the challenge to observing 3C 273 is finding it….


Finders, Finders Everywhere

Three kinds of finders Not so long ago, finders were little straight-through refractor telescopes and your only choice was the size. Today we have many more choices, and while personal preference is a major factor in picking a finder, not all finders work equally well when faced with light pollution. When dealing with significant light pollution, I've found that a green laser finder combined with a traditional finder-scope works best.

Let me explain why and share my thoughts on how the various types of finders work under washed-out skies....


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