The Lake County Astronomical Society

Light Site Viewing - Part 2

Joe Shuster

In part 1 of this topic, I described the unattractive conditions for light site astronomy. These included ambient lighting and sky obstructions from trees and buildings. But we do light site viewing to meet the public. So in this astronomy wasteland environment we need to use the meager resources we have to survive, much like a castaway on a deserted island. Fortunately there's enough to help us survive and succeed if we plan well.

The first night object that anyone notices is the moon. For veteran astronomers, the moon can lose its appeal (and even become a source of scorn). But the moon is the prime object to share in ad hoc outreach events. Kids have seen the moon in the sky and when they look through the eyepiece they realize that there are ways of seeing something new in something familiar. Something that was far is closer. It was smooth to the naked eye but rugged and rough through the telescope. It's a place that sees sunrises and sunsets like the Earth. The moon is the light site astronomer's principle resource and it is horrible news if it's not there.

In fact, it's so important to have the moon up that we only schedule these events for such nights. So we call these events "moon parties" to contrast with our darker "star parties".

The moon is best positioned and interesting from 4 days to 10 days after the new moon. This period covers a nice crescent through late gibbous phases. In my personal opinion the phase of the moon at first quarter and the following two days offer the most interesting features through a telescope. Also on these days the elevation at sunset is high so there's less atmospheric interference and easier aiming.

Because the moon is the primary feature of the event we don't need to wait until after twilight to start the event. The moon can be enjoyed without perfect darkness. This gives us some flexibility in scheduling and allows for school night events even in May or late summer when the sunset is late. And in the late fall and winter we can start a moon party as early as 4:30 pm if we want depending on the phase of the moon.

Another power of the moon is its ability to poke through clouds. A moon party can continue despite clouds that would wipe out a star party. The same can apply for the brighter planets - Mars, Jupiter, Saturn, and Venus. Of course the conditions at a light site limit what you can see. Your eyes never get dark adapted (especially if you sneak a moon peek) so dim gas clouds, most globular clusters and many open clusters are nearly invisible. The "regular suspects" of a star party aren't invited to a moon party. Double stars still punch through the brightness nicely, though, so knowing a few interesting double stars can spice up the event you want to see something other than a planet or the moon.

Constellations can be a challenge because stars dimmer than 2nd magnitude are very hard to see. The old warhorses like Orion, Leo, Cassiopeia, etc. are visible, but forget Perseus, Libra, Lyra and other constellations that depend on dim stars.

Some of the tools we in the dark are less effective. Red flashlights are laughably unnecessary - there's plenty of surrounding white light and no need to protect night vision. Green lasers are much less effective and the weaker ones are virtually useless. The good news is that moon maps, and star charts are easy to read and that dropped small part is easy to find in the "bright".

Aligning your goto mount can be difficult. Distinguishing alignment stars through trees can be a big chore. The red dot finder that works fine in the dark can dim an alignment star too much so expect to spend a little more time than usual in alignment.

Another curious aspect is that we can actually see our fellow astronomers enjoying their hobby instead of just hearing them. That takes some getting used to. Also, flash photography is much less disruptive and we should be able to get valuable photos of people of all ages doing astronomy at these events. Some video is probably possible in the brighter light sites.

So we've reviewed the differences between star parties in the dark and moon parties at a light site. In part 3, I'll coach you through your first moon party - from preparation to delivery.