lengths not transmitted by the ﬁlters). Once you have the images, you can then compare them with published pictures, observe the diﬀerences in the distribution of H+ compared to O++, and perhaps measure the ﬂux in the nebula compared to that in the star.
An alternative project would be to image a bright H II region. In this case, we would observe the nebula through the Hα ﬁlter and also through a ﬁlter centered on the Hβ line at 486.1 µm. These lines are always emitted with a constant intensity ratio, Hα/Hβ = 2.8.
However, the ratio we observe may be diﬀerent because the Hβ line suﬀers more absorption by interstellar dust than the Hα line. By studying the variations in this line ratio, we can map out the distribution of dust in the nebula. The problem with this project is that the Orion Nebula, which is by far the best H II region, can only be observed in the early morning hours at this time of year!
We want to image planetary nebulae of suﬃcient size to be able to study their shapes.
Since nebulae of this size are faint, all groups should start with the Ring Nebula (NGC 6720, M 57), which is probably the easiest object to ﬁnd. It is in the constellation of Lyra, and the nebula is located almost exactly between two naked-eye stars. The nebula itself looks like a faint “smoke ring” in the main telescope. Look up the RA and Dec and ﬁnd the object on a star chart before you go out to observe.
You will observe a second planetary nebula in addition to the Ring Nebula. You will want to pick a bright planetary nebula which has as large a size as possible without exceeding the ﬁeld of view covered by the CCD camera. You will ﬁnd the ﬁeld of view of the CCD in the hand-out on the 14” telescope. You also want to pick an object that is high in the sky sometime during the evening (or early morning) hours. Look at the illustrations in the catalog to see what sort of structure the nebula has and if the central star is visible.
It would be nice if you could observe the central star. (In principle, such observations would allow 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 use