July 2010

Star-hopping Tutorial: Lesson One (M57)

Illustration of a chart of Lyra such as would be used for star hoppingStar-hopping is one of the most valuable skills in amateur astronomy. In the days before computerized mounts and GPS, star-hopping was the only way to find interesting objects. Thanks to the steady march of technology, not as many amateurs today are proficient star-hoppers. In fact, quite a few amateurs have never star-hopped. Still, for many of us without computerized mounts, star-hopping remains a critical skill. Washed-out skies in particular can really test your star-hopping skills: when only 3rd or 4th magnitude stars are visible, it can be a pretty long hop from the nearest visible star to your target. Even if you have a computerized mount, star-hopping can be useful in light-polluted skies: with many faint fuzzies at the ragged edge of visibility, star-hopping techniques can confirm that you are indeed looking in the right place.

To help you master star-hopping I am planning a series of tutorials, starting with the simplest of star-hops and continuing with successively more challenging star-hops. Each one will end in an interesting object suitable for viewing with a modest telescope under washed-out skies. We start with a very simple star-hop from Vega to M57, the Ring Nebula...

Other tutorials in the series:  Lesson 2, Lesson 3


Flock It!

Photo of Protostar peel-and-stick flocking paperIf you have a Dobsonian or Newtonian reflector, flocking is a great way to reduce stray light and improve the contrast. What is flocking? It simply means lining or painting the inside of your telescope with something that absorbs light—ideally something that absorbs close to 100% of visible light. Most telescope insides are painted flat black, but that usually doesn’t do a particularly good job of absorbing incident light. If you don’t believe me, look down the inside of your telescope tube in the daylight: is it truly pitch black or just dark gray?

Flocking is particularly helpful in light-polluted environments because there is so much more stray light to eliminate. Think of it this way: if you are in a really, really dark site, flocking doesn’t matter much because there is essentially no stray light. In fact, in really dark skies, you don’t even need a light shroud around a truss-tube telescope—there is just no light to leak into your light path. In contrast, your typical urban or sub-urban environment has plenty of stray light sources: the neighbor’s porch light or bedroom light, the nearby street light, the sky-glow from downtown, and even the light-gray background of the sky itself. If any of this light gets into your eyepiece, it contributes to brightening the background and killing the contrast.

Now flocking is pretty easy and one of the secrets is that you only need to flock relatively small portions of your telescope to get essentially all of the benefits...