July 2009

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....


Some Thoughts About Filters

All kinds of filters

There are basically two kinds of astronomical filters: color filters primarily intended for use on planets (although they have some other uses), and used primarily to enhance contrast on certain kinds of nebulas. Nebula filters can help in seeing through light pollution. Color filters do not.

But it isn't quite as simple as that....


Welcome to Washed-out Astronomy

This web site is dedicated to helping amateur astronomers make the most of washed-out skies. As much as we all dream of having dark skies, many of us unfortunately live in areas where the skies are washed-out by light pollution. We many not have access to a decent dark site, and even if we do, we don't always have the time or energy to go there. So what can we do to get the most enjoyment of the skies we have? What kinds of celestial objects can we focus on? What objects are within reach? What can we do to see things better? Are there equipment tweaks that help? These questions are what this site is about. Everything here touches in some way to the question of observing the heavens under washed-out skies.


Edmund 4.25" Palomar Jr. Newtonian

Image of Edmund Palomar Jr focuser and finderMy oldest scope is an Edmund Palomar Jr (Pal Jr). It’s a 4.25 inch (108mm) Newtonian reflector on a German equatorial mount. It’s been in regular use ever since I got it in 1973. These days I use it primarily for solar observing using a Baader AstroSolar Safety Film aperture filter. I also use it to compare views with my Zhumell 10 inch (250mm) Dobsonian (Z-10) and to verify what a smaller aperture can show under washed-out skies.

The optics on the Pal Jr are surprisingly good, consistently showing picture-perfect diffraction patterns. It gives great views of the planets and splits η Orionis whenever the seeing is decent. In dark skies, it’s shown me most of the Messier objects and plenty of NGCs. In washed-out skies it still gives good views of double stars, open clusters, the brighter globular clusters (without any hints of resolution), and the brighter nebulas (M27, M42, M57), but apart from M31 it is exceptionally hard to see any galaxies with it. I’ve made a point of including observations with the Pal Jr throughout Washed-out Astronomy to balance the Z-10 view with a smaller aperture view.

The most interesting thing about the Pal Jr is that it was hit by lightening some years ago….



Pluto reaches somewhere between magnitude 13.8 and 14.1 at opposition making it a rather challenging object to see from washed-out skies. But Pluto’s tiny size helps us pull it out of the light pollution: because it is star-like, we can use high magnification to improve the contrast. Even from my light polluted front yard, I’ve seen stars of this magnitude with my 10 inch Dob using moderate to high magnification (150x to 250x). So in theory, Pluto is within reach.

Unfortunately, Pluto is currently located in Sagittarius. This is not good. That puts Pluto low on the horizon (and I have a particularly cluttered southern horizon). It also brings Pluto into view during the hazy months of summer, when transparency in the Washington DC area is consistently poor. Even worse, it puts Pluto right in the middle of the Milky Way, with lots of other stars of similar brightness. if you think finding a needle in a haystack is hard, try hunting for a particular 14th magnitude star in the middle of the Milky Way....