By Anna Edmonds
Have you been looking at Venus this past month? The beautiful, large, clear light in the morning sky? In fact, it’s been so bright that if you knew right where it was, you could still see it even after the sun rose. No wonder it was named for a goddess—and with Earth the only goddesses so honored!
But Venus isn’t a star. It shines like a star; it’s mostly visible when the stars are out. However, it has a limited area in which it can be found; and it has a limited time: It stays close to the Sun, so, for instance, you’ll never see it in the east in the evening. And, it wanders around: Sometimes you can see it just at dawn—the Morning Star, and then sometimes it’s around after sunset—the Evening Star. “Wanderer” is what its name means, and that of eight more of our neighbors—the “planets.”
How can you tell whether the light you’re seeing in the sky is a star or a planet? The first answer I was given to this question was that stars twinkle but planets shine steadily. Now with my older eyes they all seem to blink on and off, so that answer doesn’t work for me. So the next answer is more complicated, and is one I’ve already hinted at: If you watch the points of light over a period of time you will notice that stars stay in the same place relative to each other: the Big Dipper always looks like the Big Dipper. But the planets move. For Venus, early in December you couldn’t help seeing it when the clouds parted and you looked southeast before the Sun was up. By spring it will be gone, lost in the sunlight. The other planets act the same: they move around relative to the fixed stars, and sometimes they disappear behind the Sun.
Therefore, another way to determine whether the light is a star or a planet is to know the stars. That’s not quite as hard as it sounds. To start you don’t have to know all the millions of them, or even to begin, all of the 6,000 that people with good eyes can see over the year without help on a clear night in a dark sky. Instead of this, you can start by learning the names of the fifteen brightest—the first magnitude—stars that are visible in our northern sky. At the same time, you can make it easier for yourself if you also learn the groups of stars—the constellations—that these stars are part of.
These fifteen first magnitude stars that are up in our northern sky (and their constellations in the parentheses) are *Aldebaran (Taurus), Altair (Aquila), Antares (Scorpius), Arcturus (Bootes), *Betelgeuse (Orion), *Capella (Auriga), *Deneb (Cygnus), Fomalhaut (Piscis Australis), *Pollux (Gemini), *Procyon (Canis Minor), *Regulus (Leo), *Rigel (Orion), *Sirius (Canis Major), Spica (Virgo) and Vega (Lyra). The ones with a “*” before the name are visible here in the early evening during the winter months. You’ll notice that there are a majority of them visible now.
Getting back to the planets, for the next two months Venus has been in the constellation Libra (that constellation has no first magnitude star); it’s moving into the region north of Antares. Of the other planets, Mars is there in Scorpius, but it’s quite dim. Jupiter is not far from Regulus; and for Saturn, Aldebaran might help you locate it. Mercury scoots around close to the Sun. It’s low in the twilight early in January and then low in the eastern morning dawn the end of January (when it will be at its brightest), and all of February.
Next time I’ll talk more about what to look for with the planets.