D e s e r t E x p o s u r e
February
2009
Constellation of the Month: Lepus, the Hare
Rabbits are pretty common in our area, but there is one in our sky as well. Looking low in the southern sky just south of Orion, you will find Lepus, the Hare. This is one of the original 48 constellations listed in the first century by Ptolemy.
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The mythology around Lepus is somewhat vague, but mostly seems to be related to the surrounding constellations. Lepus is portrayed as the prey for the Big Dog, Canis Major, and as the quarry of Orion the Hunter. To the Arabs, this collection of stars represented four camels at an oasis instead of a hare.
A morality story that does not involve the surrounding figures is told to us by Hyginus, a Latin author from the early first century. On the Greek isle of Leros, there were no hares and people lived well. One day, a man brought a pregnant female hare to the island. Everyone thought hares were great animals to have around and started raising them. The island was soon swarming with hares, which decimated the vegetation. Soon the population was starving and they knew they had to get rid of the hares. They banded together and drove the hares off the island. As a reminder that moderation was important in all things, they put an image of the hare into the sky, giving us the constellation Lepus.
Lepus is 51st among the constellations in terms of area, just west of the Milky Way. Lepus has only two interesting objects: the globular cluster M79 and Hind's Crimson Star.
M79, the 79th object on Charles Messier's list of fuzzy objects that are not comets, was discovered in 1780 by French astronomer Pierre Mchain. A little on the faint side at magnitude 8.6, M79 is 8.7 minutes of arc across. This globular is 60,000 light years away from the center of our Milky Way galaxy — so far away that some astronomers believe it is actually associated with the Canis Major dwarf galaxy instead. That dwarf galaxy is 24.5 degrees from M79, and even closer to the Milky Way at 42,000 light years.
There are dwarf galaxies scattered throughout our sky, but they are small, faint and hard to recognize, so they are more recent discoveries. The Canis Major dwarf galaxy was just discovered in November 2003, hiding behind the dust and gas in the plane of our Milky Way galaxy. It is believed to contain over a billion stars, many of them red giants in the twilight of their life cycle. This galaxy is so close to us that astronomers believe the Milky Way's gravity is tearing it apart. If so, its stars, dust and gas will someday be a part of our galaxy.
Much closer to us is Hind's Crimson Star, named for John Russell Hind, an English astronomer who first spotted it from the private observatory of George Bishop in 1845. Hind's Crimson Star is one of the reddest-looking stars in the sky. On the western border that Lepus shares with Eridanus, Hind's Crimson Star is also known as R Leporis or SAO 150058. This star is a variable that at its brightest is magnitude 5.5. But it is at its faintest (magnitude 11.7) that the red color really comes out. The variability is caused by the build-up of carbon in the star's outer atmosphere. The carbon absorbs the blue light coming from the star, leaving only the red light to get through. The more carbon that builds up in the star's atmosphere, the redder and fainter the star becomes.
Hence, carbon stars like R Leporis are reddest when faintest. The carbon is eventually blown off into space, clearing the atmosphere and bringing the star back to its brightest and bluest. The cycle then begins again. The blow-off occurs every 427 to 432 days, giving one out of every 14 months with the R Leporis at its faintest and reddest. This happened back in June 2008 and will happen again in August 2009.
The Planets for February 2009
After all the planets visible in our early-evening sky for the last few months, we are now left with only the Goddess of Beauty gracing us with her brilliant presence. Venus is about a third of the way up in our western sky as it gets dark, setting about 9 p.m. Venus is in Pisces all month as it stops its eastward motion among the stars and begins to slide back toward the horizon along with the rest of Pisces. On Feb. 15, Venus is 36.9 second-of-arc across and is a 33-percent illuminated crescent at magnitude -4.6. It will continue to become more of a crescent and get larger and fainter as the month goes on.
In our eastern sky around 7:30 p.m., Saturn rises for some of the best observing opportunities of the year. Visible the rest of the night, Saturn will make a good target as the Rings continue to close. Drifting westward among the stars of southeastern Leo, Saturn is 19.6 seconds-of-arc across at midmonth. The Rings are 44.4 seconds-of-arc across, with only a 1.8 degree tilt, the southern face still showing. Saturn is magnitude +0.6.
The rest of the classical planets appear in our morning sky, coming up shortly before the Sun. First up is Mercury, at least for most of February. It starts the month in Sagittarius. Mercury reaches greatest western elongation on Feb. 13, then turns back around, heading eastward for the Sun, moving into Capricornus. It gets lower each day thereafter. At greatest western elongation, Mercury is magnitude 0.0 and 60 percent illuminated (decreasing). Mercury is 6.9 seconds-of-arc across.
Mars and Jupiter rise before the Sun does, but they are very low in the east-southeastern sky. They are not worth looking at telescopically, as they will be better placed for observing later in the year. So get ready for great views of Jupiter and Mars and "keep watching the sky"!
An amateur astronomer for more than 35 years, Bert Stevens
is co-director of Desert Moon Observatory in Las Cruces.
Watch the Skies (all times MST) Feb. 1, 4:13 p.m. — First Quarter Moon Feb. 9, 7:49 a.m. — Full Moon Feb. 13, 2 p.m. — Mercury farthest west of the Sun (26 degrees) Feb. 16, 2:37 p.m. — Last Quarter Moon Feb. 17, 3 a.m. — Mars 0.6 degree south of Jupiter Feb. 19, 8 a.m. — Venus greatest brilliance Feb.23, 8 p.m. — Mercury 0.6 degree south of Jupiter Feb. 24, 6:35 p.m. — New Moon Feb. 27, 6:30 p.m. — Venus 1.0 degree north of Moon |