Serpent Bearer, are Serpens Caput (the Serpent’s Head) and Serpens Cauda (the Serpent’s Tail).
The individual stars in a constellation often have no relation to each other except for their proximity in the sky as visible from Earth. In space, the stars that make up a constellation may be completely unrelated to one another, with some located relatively near Earth and others located at much greater distances in space. But they make a simple pattern for observers on Earth to enjoy.
As a rule, the brighter stars in a constellation were assigned a Greek letter, either by the ancient Greeks or by astronomers of later civilizations. In each constellation, the brightest star was labeled alpha, the first letter of the Greek alphabet. The next brightest star was beta, the second Greek letter, and so on down to omega, the final letter of the 24-character Greek alphabet. (The astronomers used only lowercase Greek letters, so you see them written as α, β, … ω.)
So Sirius, the brightest star in the night sky – in Canis Major, the Great Dog – is called Alpha Canis Majoris. (Astronomers add a suffix here or there to put star names in the Latin genitive case; scientists have always liked Latin.) Table 1-1 shows a list of the Greek alphabet, in order, with the names of the letters and their corresponding symbols.
TABLE 1-1 The Greek Alphabet
TABLE 1-2 The Constellations and Their Brightest Stars
Astronomers didn’t coin special names such as Sirius for every star in Canis Major, so they named them with Greek letters or other symbols. In fact, some constellations don’t have a single named star. (Don’t fall for those advertisements that offer to name a star for a fee. The International Astronomical Union doesn’t recognize purchased star names.) In other constellations, astronomers assigned Greek letters, but they could see more stars than the 24 Greek letters. Therefore, astronomers gave some stars Arabic numbers or letters from the Roman alphabet, or numbers in professional catalogues. So you see star names such as 61 Cygni, b Vulpeculae, HR 1516, and more. You may even run across the star names RU Lupi and YY Sex. (I’m not making this up.) But as with any other star, you can recognize them by their positions in the sky (as tabulated in star lists), their brightness, their color, or other properties, if not their names.
When you look at the constellations today, you see many exceptions to the rule that the Greek-letter star names correspond to the respective brightness of the stars in a constellation. The exceptions exist because
❯❯ The letter names were based on inaccurate naked-eye observations of brightness.
❯❯ Over the years, star atlas authors changed constellation boundaries, moving some stars from one constellation into another that included previously named stars.
❯❯ Some astronomers mapped out small and Southern Hemisphere constellations long after the Greek period, and they didn’t always follow the lettering practice.
❯❯ The brightness of some stars has changed over the centuries since the ancient Greeks charted them.
A good (or bad) example is the constellation Vulpecula, the Fox, in which only one of the stars (alpha) has a Greek letter.
Because alpha isn’t always the brightest star in a constellation, astronomers needed another term to describe that exalted status, and lucida is the word (from the Latin word lucidus, meaning “bright” or “shining”). The lucida of Canis Major is Sirius, the alpha star, but the lucida of Orion, the Hunter, is Rigel, which is Beta Orionis. The lucida of Leo Minor, the Little Lion (a particularly inconspicuous constellation), is 46 Leo Minoris.
Table 1-2 lists the 88 constellations, the brightest star in each, and the magnitude of that star. Magnitude is a measure of a star’s brightness. (I talk about magnitudes in the later section “The smaller, the brighter: Getting to the root of magnitudes.”) When the lucida of a constellation is the alpha star and has a name, I list only the name. For example, in Auriga, the Charioteer, the brightest star (Alpha Aurigae) is Capella. But when the lucida isn’t an alpha, I give its Greek letter or other designation in parentheses. For example, the lucida of Cancer, the Crab, is Al Tarf, which is Beta Cancri.
Identifying stars would be much easier if they had little name tags that you could see through your telescope. If you have a smartphone, you can download an app to identify the stars for you. Just download a sky map or planetarium app (such as Sky Safari, Star Walk, or Google Sky Map) and face the phone toward the sky. The app generates a map of the constellations in the general direction your phone is facing. With some apps, when you touch the image of a star, its name appears. (I describe more astronomy apps in Chapter 2; for the full scoop on stars, check out Chapter 11.)
Naming stars was easy enough for astronomers. But what about all those other objects in the sky – galaxies, nebulae, star clusters, and the like (which I cover in Part 3)? Charles Messier (1730–1817), a French astronomer, created a numbered list of about 100 fuzzy sky objects. His list is known as the Messier Catalog, and now when you hear the Andromeda Galaxy called by its scientific name, M31, you know that it stands for number 31 in the Catalog. Today 110 objects make up the standard Messier Catalog.
Experienced amateur astronomers often engage in Messier marathons, in which each person tries to observe every object in the Messier Catalog during a single long night. But in a marathon, you don’t have time to enjoy an individual nebula, star cluster, or galaxy. My advice is to take it slow and savor their individual visual delights. A wonderful book on the Messier objects, which includes hints
