Planning a Night of Astronomy
Here in the Seattle area, we get lots of cloudy days — and nights. So when there are clear viewing opportunities, it’s always nice to maximize overall productivity instead of spending the night trying to figure out what would be interesting to see, slewing all over the place and not giving objects the attention they deserve.
Some choices — like whether or not one is planning to do visual observing or imaging are pretty easy to decide — but then what are you planning to look at? That pair of binoculars isn’t going to work so great on the Virgo Cluster, and your big aperture small field of view catadioptric reflector might only give you the core of M31. So, while you can bounce around with GOTO and tour-modes, having an idea of what to see will really maximize the experience!
Weather and Sky Conditions
First comes the moon and the weather. If the overall sky conditions aren’t going to be good (windy, humid, cloudy) or there is a big bright moon out, one might want to focus on brighter objects like star clusters, planets, binaries, and even some nebula (especially ones with filters — OIII or otherwise). However, if you have one of those rare opportunities where you have great seeing conditions, dark skies — then all sorts of deep sky objects will open up to you. For overall weather forecast, I use weather.com. However, another great resource is the ClearDarkSky chart which factors in many different criteria to try to determine what your overall seeing will be.
Gear! Or, “What to Bring to My Dark Sky Site”
So you have a decent idea of the types of things you are hoping to catch a glimpse of (or image!). Do you need a wide field refractor, or your long focal length mega-aperture monster to see it? Will an alt-az configuration work well for your visual eyepieces, or do you need an rotator (or equatorial mount) for longer exposures? What about power? Are the batteries charged, or can you plug in somewhere? Of course, don’t forget about the dreaded Mosquitos! Warm clothes, blankets, and a healthy dose of alcohol… The Saguaro Astronomy Club has a very nice and simple checklist. If you are planning to travel to a special dark sky site, especially a far away one, you’d be well served to at least look at it!
Object Selection Criteria
The first step here is to come up with an observation list. Many observation lists are based on apparent magnitude, or how bright the object will appear to be as seen from Earth. This is certainly useful, but it can have you slewing all over the sky to pick out objects. Another is the aforementioned “Tour Mode”. The concept here is simple: Pick a region of the sky (generally a constellation), and then view objects within that constellation only. This is a pretty nifty way to view a lot of objects in a short time since the amount of slew time is kept to a minimum. It also works well when you have a smaller patch of open sky from your viewing site.
One often overlooked selection technique is to select by apparent size. Like apparent magnitude, apparent size is how large the object will appear to be from Earth. For example, there could be a galaxy out there, a real whopper in actual size, but it is so far away it looks like nothing more than a tiny spec. (Keep in mind that when imaging, you can typically see higher magnitude objects (i.e. darker objects) since the camera collects up light for a longer period than your eye will “collect and show you”). OTOH, there could be a smallish galaxy nearby that fills up the eyepiece. Apparent size is a great way to select objects especially if you know what your ideal observing field of view will be.
For example, I have a wide field refractor, the Televue NP101is. This scope can provide nearly a 3 degree field of view – 180 arc minutes. Viewing an object which is only 1 arc minute in diameter such as the popular M57 Ring Nebula is only going to use up 1/180 of your eyepiece in this configuration. On the other hand, the CPC 1100 at 100x will give a fairly narrow 0.6 degree field of view — or 36 arc minutes. Clearly this will give a much large image in the eyepiece as a reasonably magnification factor. Unfortunately, there are a lot more objects with a small apparent size than a large apparent size, so be ready to break out big aperture if you are thinking of going for small stuff! One fabulous resource for selection by size is the MAPUG List of Nice Objects. Be sure to check it out!
Other Object Selection Resources
There are a ton of resources available to find objects. Of course, Astronomy and Sky and Telescope magazine have monthly inserts with interesting things floating around out there. One of the simplest resources is Skymaps, which has a map of the sky and many keen, easy-to-find bright objects. If you’re new to the hobby, these lists are a fantastic place to start. Stellarium is a wonderful free planetarium which can help identify objects in a specific region, their RA/DEC location, magnitude, and so forth. It can also really help you learn the sky quickly. Here are a few more resources and guides:
There are many other lists out there on the net; when you come across one, please feel free to comment and link to it! Clear Skies!