Usual Suspects List The following is a list of deep sky objects that can be seen by inexperienced amateurs using modest equipment under average conditions. Of course, what can be seen is a bit open to interpretation. This list contains objects that are verified as being visible to 20 × 50 binoculars from a suburban sky in southern England. From southern Europe and the United States, there are some objects that would be difficult to see. However, an experienced observer would be able to tick the list off armed with good skies and a quality pair of 30 mm binoculars. Some of them may also be visible in small telescopes, but their large apparent angular size means that a telescope only shows a small part of them. If you use larger binoculars (say 60 mm or larger) most of the time, you should be able to see objects on this list under more difficult conditions and see a few more difficult objects under better conditions. 333 334 The Science and Art of Using Telescopes 16/17 Draconi Facts at a Glance Object Type Double star Declination +52 deg 18 min Right ascension 19 h 46.4 min Magnitude Components of 5.4 and 5.5, and 17 has a fainter companion of magnitude 6.4 Separation 90.3 arcsec and 3.4 arcsec Description 16 and 17 Draconi form a double star system, well within the range of most binoculars. In an 80 mm refractor or larger, 17 Draconi shows a fainter companion of magnitude 6.4. Fig. 1. 16/17 Draconi. Usual Suspects List 335 This system is circumpolar from the UK and most of Canada but is best placed for evening viewing in late summer. It can be difficult to pho- tograph without timed exposure, as the components are quite faint. Albireo (Beta Cygni) Facts at a Glance Object type Double star Declination +27 deg 58 min Right ascension 19 h 30.7 min Magnitude Combined 3.1 with 3rd and 5th magnitude components Separation 34 arcsec Description After the Mizar/Alcor pairing in the Plough, Albireo is probably the most famous double star in the Northern Hemisphere. It is often a “hit” at star parties and something to impress the neighbors with if they see you out with a telescope. The color contrast between the two stars makes it stand out as one of the most beautiful objects of its type. Being at the head of Cygnus, it is easy to find with the naked eye or in a binocular sweep, but it can get irritatingly difficult though a telescope if your finderscope is not precisely aligned. Unlike Mizar and Alcor, it is a true binary star. It can sometimes be split in binoculars as small as 25 mm. Just about any telescope will be able to split it, and this is one of the few objects that is not improved by a larger telescope. The two stars have been resolved (but not the space between them, giving the “peanut effect”) with 8 × 21 binoculars. The stars’ components have been reported as various colors. The pri- mary often appears orange in many binoculars and the secondary blue, although the secondary component has been reported as green. Most photographs show the primary as yellow/orange and the secondary as blue. It is the color contrast that makes this double star a popular and well known object. Seen under the most appallingly bad conditions, such as thin cloud, light-polluted skies, and twilight and is an easy object to show at star par- ties when little or nothing else is visible. 336 The Science and Art of Using Telescopes Fig. 2. Albireo by Nick Howes. Usual Suspects List 337 Alcor/Mizar (60 Ursae Majoris/ Zeta Ursae Majoris) Facts at a Glance Object type Double star Declination +54 deg 56 min Right ascension 13 h 23.9 min Magnitude Alcor is magnitude 4.0, Mizar has components of 2.3 and 4.0, with a combined magnitude of 2.1 Separation Alcor and Mizar are separated by 708.7 arcsec (nearly 12 arcmin), and Mizar’s components are separated by 14.4 arcsec Description This is the most famous double star in the sky and was featured in the film “Deep Impact.” The Plough (in the UK) or Big Dipper (US) is well known even to people who do not follow astronomy. Alcor and Mizar are far enough apart that they can be split without binoculars on a good night, but, as often as not, a small pair of binoculars is needed to bring Alcor out of Mizar’s glare. A telescope is needed to split Mizar into its two components and only a small telescope, with medium magnification (around 40× but sometimes less), will do it. This is a nice trick to get things going at star parties where the seeing is poor and there are not many planets about. It has been reported as being split with 80 mm binoculars. 338 The Science and Art of Using Telescopes Fig. 3. Mizar and Alcor. Usual Suspects List 339 Andromeda Galaxy (M31) Facts at a Glance Object type Galaxy (Spiral) Declination +41 deg 16 min Right ascension 00 h 42.7 min Magnitude 3.1 Apparent angular size 3 × 1 deg Description The Andromeda Galaxy (M31) has inspired a lot of science fiction. Its photographs have decorated the covers of several books. Despite its extreme distance (over 2 million light years), it can be seen as a small fuzzy patch with the naked eye from a suitably dark site. On a really good night, it can be truly breathtaking through suitable instruments. Most nights, it falls rather short of that, as it is easily affected by thin cloud, moonlight, and light pollution, yet is still worth seeing as long as there are stars in the sky. Despite its incredible distance, it is actually the largest natural object in the northern sky, being about six times larger than the apparent size of the Sun and the Moon. Through small binoculars, Andromeda appears as a large fuzzy patch, somewhat larger than the full Moon. Larger binoculars (60 mm plus) show its full extent of 3° width on a good night and actually show some of its structure of a nucleus and subtle shading in the outlying regions. Its large apparent size can cause problems when using a telescope. You can get the whole galaxy in using an 80 mm short tube refractor, which can deliver a 4° field of view at low magnification. This is about as good as you can get if you want to see the whole galaxy in one look. The picture shows the type of view you might expect on a good night. The only way to improve on this is very large tripod-mounted binoculars of 100 mm plus aperture. Moving up to a larger telescope (125 mm plus) will allow you to see the nucleus in more detail, although its best to keep the magnification low. You can also pick up the companion galaxies M110 and M32. 340 The Science and Art of Using Telescopes Fig. 4. Andromeda Galaxy (photograph by Brian Woosnam). Usual Suspects List 341 Beehive Facts at a Glance Object type Open star cluster Declination +19 deg 59 min Right ascension 8 h 40.1 min Magnitude Combined magnitude of about 4 Apparent angular size 2 deg Description This is a star cluster similar in nature to the Pleiades and Hyades but is further away and much fainter. It is theoretically visible to the naked eye but needs a dark sky and pristine conditions. Most astronomers have only ever seen it in binoculars, although quite small ones will show it clearly. Its name is certainly a good description. These stars are easiest to find when both Pollux (Beta Geminorum) and Regulus (Alpha Leonis) are both above the horizon, as it is about halfway between the two stars. From the United Kingdom and Canada, the Beehive can be seen from about midnight in November to just after darkness in July. 342 The Science and Art of Using Telescopes Coathanger Facts at a Glance Object type Asterism Declination +20 deg 11 min Right ascension 19 h 25.4 min Magnitude Combined magnitude of about 4 Apparent angular size 1 deg Description This is an asterism in the constellation of Vulpecula. It looks just like a coathanger, hence its name. It is a pattern of 5th and 6th magnitude stars and is also in a rich part of the Milky Way, so the general view is rather good. It was once thought to be a true star cluster, but most of its stars are at various distances, so are not physically related. From the United Kingdom and Canada, the Coathanger can be seen from about midnight in May to just after darkness in December. Usual Suspects List 343 Delta Lyrae Facts at a Glance Object type Double star Declination +36 deg 58 min; +36 deg 54 min Right ascension 18 h 53.7 min; 18 h 54.5 min Magnitude 5.6 and 4.5 magnitude components, each with fainter companions of 9.3 and 11.2, respectively Separation About 4 arcmin and 174.6 and 86.2 arcsec for the fainter companions Description Delta Lyrae is an easy double star, well within the range of even the most modest binoculars. The only problem you might get is that the fainter companion might not be visible where transparency is poor. It is almost circumpolar from many places in the UK and Canada but is best placed for evening viewing in late summer.