you to calculate the temperature of the star.) To save time, look at a list of nebulae suitable for observation by amateur astronomers;
that way you will not waste time on objects which are too faint. But at some point you should turn to the Strasbourg-ESO Catalogue to obtain basic information such as the size, the ﬂux in Hβ (Hα is always about 3 times brighter) and in [O III] λ5007. You will want nebulae that have [O III] as bright or brighter than Hα. The larger the value of Hβ the better – note that the number listed is the negative logarithm of the ﬂux, so a smaller number is a brighter nebula. Traditionally, observers would prepare a ﬁnding chart to locate the object, but our telescopes should point accurately enough to get it into the ﬁeld of view by just entering the coordinates or its name. If you want to locate it on a chart, we have found that the atlas “URANOMETRIA 2000.0” by Tirion, Rappaport, and Lovi (in the Astronomy Library and at the Observatory) has a convenient scale. You should also have at least one extra back-up object.
With regard to the H II regions, it is unfortunate that the only really good target is the Orion Nebula, which does not rise until the early morning hours (i.e., after 3:00 AM!) at this time of year. If you wish to do the H II region, we can arrange to try it, but we will have to make arrangements for a mutually acceptable date(s).
You should dress very warmly. You are likely to get much colder than you might expect, since you’ll be motionless outside at night for several hours. Dress in layers. Be sure to have a wind-proof shell. Especially later in the fall, gloves and a warm hat are a necessity. The concrete ﬂoor gets very cold, so it’s best to have warm, thick socks and thick rubber-soled shoes. A thermos of a warm drink is also a good idea. You may wish to bring a ﬂashlight.
You should bring a notebook and pen for your notes.
Because of problems with the 20” telescope in the West Bay, we will have to use the Celestron 14” telescope in the East Bay. (The 20” telescope uses the (relatively) new Apogee CCD camera. Unfortunately, we don’t have operating instructions for the Apogee written up yet.) This handout is written, for the most part, as if you were using the 14” telescope.
Before coming to the observatory, you should read through the instructions for operating the telescope.
You should bring the relevant pages to the observatory with you when you observe.
3.2. Dark Frames
Thermal electrons (ie electrons which get excited due to the non-zero temperature of the CCD chip) get collected by the CCD just like electrons liberated by photons striking the CCD, and dark and light electrons obviously cannot be distinguished. The number of thermal electrons collected increases linearly with the exposure time. Consequently, one needs a dark frame with an exposure identical to the exposure on the object (called the light frame). This must be subtracted from the exposure of your object. Note that since any exposure has a bias oﬀset, subtraction of the dark frame from the light frame also automatically does the bias subtraction.
Note that you must keep a record of all the exposure times for useful exposures, and then be sure that you have obtained and saved dark frames of identical exposure time. By the way, since no light enters the telescope for a dark frame, obviously the ﬁlter does not matter for a dark frame — all that matters is the exposure time. So a dark frame can be subtracted from any frame of identical exposure time, regardless of which ﬁlter was used.
Actually, the 14” CCD observing software will usually take both light and dark frames and automatically subtract the dark frame from the light frame. If this is done, you do not subtract a dark frame during the later reduction stages, since it has already been done.
However, since telescope time in good weather is hard to get, we might prefer to obtain the dark frames after astronomical observations in order to complete the astronomical observations as quickly as possible, in case the weather turns bad or the nebula sets. If this m