The Constellation Leo


  1. We will now return to the Dipper and follow the two stars at the back of the cup down, leading us to the star Regulus in the Zodiac Constellation Leo the Lion, which dominates the center of the Spring sky. {Trace out Leo, point out the stars Regulus & Denebola} This is a great constellation that looks very much like what it is supposed to be. Some star charts show Leo walking, but to me the stars powerfully suggest the Big Cat is in a reclining position. His head is formed by a backward question mark, an asterism that is commonly called The Sickle. The star to the right of Regulus is his forepaw, and the bright triangle to the left is the lion's rear haunch.

  2. You can use the Sickle to gauge how good your sky is... the clearer the sky, the fainter the magnitudes you can see. Starting with 1st magnitude Regulus we skip a star and come to 2nd magnitude g (gamma) Leonis, then as we go up, the back of Leo's head and his nose are both 3rd magnitude stars, and his topknot is 4th magnitude. His eye, half-way between the nose & topknot, is 5th magnitude and if you can see it, indicates you have an excellent sky. His ear is an itty-bitty 6th magnitude star which, if you can see it, tells you that your sky is the best you're going to get.

  3. Regulus is the brightest star in Leo and is sometimes known as the Heart of the Lion, "Cor Leonis". If you can get the binoculars focused on this star you'll find a surprise waiting there for you... up and to the right -- a fainter, golden yellow star right next to the brilliant blue-white Regulus. (If the sky isn't dark enough we might have to use the telescope to see it.) The fainter star is in orbit about Regulus, and in fact that fainter star is really two stars, too close for us to resolve, a yellow dwarf and a red dwarf. So you are looking at a three-star system. That may seem weird to you, three stars locked in orbit together, but in fact three quarters of the stars you see up there have at least one, maybe two or more companions. So we're the weird ones, circling a single solitary star -- the sun.

  4. Meanwhile we've gotten the telescope on another double star, one you can only see with the telescope. We are looking at g (gamma) Leonis, a pair of stars 90 light years away and circling each other at a distance about three times the size of Neptune's orbit.

    As you look at this pair you might notice a tiny little ring around each star. This is a "diffraction ring" -- it's an interference pattern caused by light waves interacting with the edge of the telescope opening. If you look through a telescope with a wider lens (or mirror), the rings will be smaller -- hence the larger the diameter of the telescope, the more detail you can see. We can just split these two stars apart -- a smaller telescope could not. Likewise if the stars were closer (less than about 4 seconds of arc) we would have trouble splitting them.

  5. Leo is, as I said, a Zodiac constellation, so as we circle around the sun, it seems to pass through this part of the sky. In fact Regulus lies almost directly on the ecliptic, meaning it lies right on the plane of our solar system. As a result, it is fairly common to see the planets pass very close to Regulus, and sometimes right in front of it, blocking out the star! Mars passes by Regulus on June 7, 2010, Venus will pass by on July 9, 2010 (as evening star), Mercury aligns with it on July 27, 2010 (as evening star) and passes by again on September 14, 2010 (again as an evening star), then again on July 27 and September 8, 2011 -- although spotting Mercury is always elusive. Mars passes it again November 10, 2011 and then takes up residence near Regulus until about June of 2012, then on the morning of October 2, 2012 we see a near-perfect conjunction of the star with Venus.

  6. Since he's in Galaxy Alley, Leo has quite a few galaxies of his own. If we have a dark night you can look with the binoculars just south of q Leonis and detect the very close pair of galaxies, M65 & M66. With the telescope we can see more detail and maybe even see a third galaxy just to the north of this bright pair, NGC3628. These three galaxies are a well-known group called the Leo Trio, a true grouping, all about 30 million light years away.

  7. Just above Leo, a little to the north, is Leo Minor, which is usually shown as just a flat triangle of the three brightest stars. But if you have a reasonably dark night and can see the dimmer stars, you can see the figure as drawn above, which gives you a little more of a clue of why on earth somebody ever called this "Leo Minor". You can actually see a miniature reflection of the figure of Leo in these fainter stars.

  8. To the left of Leo you might be able to see a wispy collection of faint stars, which could very well be the tuft of the lion's tail. In fact at one time that is precisely what those stars were considered to be, before they became a constellation of their own, known as Coma Berenices or "Berenice's Hair". {Trace out Coma Berenices, showing the right-angle stand and the hair hanging from it.} This wisp of stars is a true cluster, and one that is very close to us. At 250 light years, only the Hyades and the Ursa Major moving group are closer.

  9. Coma Berenices is the home of the galactic north pole, just a nudge below that star half-way between b and g, a star known as "31 Comae Berenices". What that means is that when you're looking at Coma Berenices you are looking directly up, out of our galaxy. It also means that when Coma Berenices is straight up in the sky, the Milky Way can't be found anywhere in the sky, because it is circling you, following the horizon all the way around you.

    Coma Berenices lies right in the middle of the Virgo cluster of galaxies, and in fact contains so much of the cluster that it is often referred to as the "Virgo-Coma Cluster". One of the best is the Black Eye Galaxy, just to the left of that little star right there {point out 35 Comae}. You can spot it with the binoculars, although we need a relatively large telescope (8" or better) to see the black eye at the center. It's actually a lane of dust that is the result of a collision with another galaxy -- literally smacking into this one and leaving it with a black eye.

  10. Now, if you look with the binoculars just slightly above and to the left (northeast) of a Comae Berenices you will find a faint fuzzy spot -- this is M53, from Messier's catalog, and once we get a telescope on it you will discover it's one of the treasures of the deep sky. This is not just any star cluster -- notice how it looks like a little globe of stars? For that reason this kind of cluster is called a "globular cluster".

    Globular clusters are rare - only about 150 are known, and they are completely different from open clusters like M35 that we saw in Gemini.

    M35 is estimated to be about 100 million years old, while M53 is estimated at about 10 BILLION years old, making it so old that it formed before the disk of the Milky Way galaxy formed! While M35 has several hundred stars in total, M53 has several hundred thousand stars. M35 is about 3000 light-years away and about 30 light-years across, M53 is 60,000 light-years away and 220 light-years across.

    These numbers are typical, so globular clusters are much, much bigger than open clusters, and they are much, much older - some are nearly as old as the universe!

  11. Coma Berenices is the only constellation in the sky whose legend is actually based on a true historical incident. The story goes back to about 200 years BC, in ancient Egypt. The king of Egypt at that time was Ptolemy, a shrewd king who ruled well, advanced Egyptian influence in the world and along with his father, established the library at Alexandria, an enormous achievement both culturally and for the academic world.

    But when the Assyrians murdered his sister, Ptolemy headed up an army on a mission of revenge. The Assyrians had a chilling reputation for ferocity, a reputation that has stayed with them right up to the present day. So Ptolemy's beautiful queen, that would be Berenice, made a promise to Aphrodite, the goddess of beauty, that if Ptolemy came back safe from his raid, she would cut off her long flowing hair and offer it to the gods.

    The king did indeed return from the sortie in one piece, the queen did indeed cut off her hair and place it in the temple, and the hair was promptly stolen that very night. The king and queen were furious and the temple guards, having slipped up, were on the brink of being put to death when the court astronomer saved them through some quick thinking. Possibly already aware of the asterism behind Leo that resembles a tuft of hair, he announced that Aphrodite was so pleased with the gift that she had taken the offering and placed it among the stars. Incredibly, the king bought it, and the guards were spared.

    So the moral is -- study your astronomy. You never know whose life you may save.

    And on that note, our tour of the Spring night sky is completed. In early spring we may have spent some time early on picking up some of the more spectacular gems of the retreating winter titans. In late spring, we have Hercules and Lyra on the rise, with the spectacular globular cluster M13 and the best planetary nebula in the sky, the Ring Nebula, as described in the Summer Sky Tour, which the more robust stargazers might stick around to see. At this point, though, we've covered quite a bit of ground and it's usually just to about time to call it a night.


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Questions

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Updated 11 November 2011