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LEPUS
The Hare
Lepus - Alexander Jamieson - 1822
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Lepus, the hare, is the last of the four winter constellations in the Orion story. Like its wild namesake, the hare keeps a low profile, and is not easy to find, hiding in the celestial undergrowth at Orion's feet.
The brightest (alpha) star in the constellation is Arneb. It is 5,700 times brighter than our Sun. Yet its apparent magnitude from Earth is only 2.58, as it resides at the very great distance of 900 light years. Because the light took 900 years to reach us, when we look at Arneb, we are seeing a "live" picture of the star as it was 900 years ago. We are looking 900 years into the past.
The second brightest (beta) star in Lepus is Nihal. It is only 70 times brighter than our Sun, yet it has an apparent magnitude of 2.85 that almost matches Arneb, and appears almost as bright as Arneb, because it is relatively close, only 150 light years away.
Lepus contains three deep sky objects, but like the hare itself, they also seem to be hiding in the undergrowth. NGC 1832 and NGC 1964 are both far away galaxies, but at magnitude 11 they are a challenge to find, even in a backyard telescope. The globular cluster M79 is considerably brighter at magnitude 8.4, but it is tricky to see. M79 is 40,000 light years away. It measures over 100 light years in diameter, and contains about 100,000 stars. Photo below by the Hubble Space Telescope.
Lepus contains a grouping of stars called a globular cluster, which was observed by Messier in 1780 and designated M79. Globular clusters are like mini-galaxies, and can contain a million stars each. They do not lie within the main spiral arms of the galaxy, but surround the galaxy in a spherical cloud, as illustrated below. Of course, if size were kept to scale in the diagram, the clusters would be no more than specks.
There are close to 200 globular clusters surrounding our Milky Way galaxy. The closest is about 8,000 light years, and the farthest about 180,000 light years. Unlike larger, true galaxies, which tend to be disk shaped, and hundreds of thousands of light years in diameter, globular clusters are compact spheres of stars, averaging only a few dozen light years in diameter.
They do not follow the rest of the stars in the spiral arms of the galaxy, but orbit the center of the galaxy in wide ranging elliptical orbits. Globular clusters are the elders of the galactic community, composed only of old and aging stars. If our Sun belonged to a globular cluster, our night sky would be very much brighter than it is now, as imagined in the famous Isaac Asimov tale Nightfall.
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