March 1999 Sky from the Keeble Observatory

Bulletin: Pluto is still a planet. OK, it's not the most important news you'll read today. I indicated last month that the IAU (International Astronomical Union) was considering a new classification for Pluto, designating it as a "trans-Neptunian Object." Tales of its impending demotion elicited responses which were surprisingly emotional, as though changing its category would somehow change something truly important. In truth, it was never really in danger. Astronomers tend to be somewhat conservative in changing traditional designations. After all, we still use the constellations to designate different regions of the sky. Any real change in nomenclature is likely as rare as a blue moon.

Speaking of which, March will be the second month this year with a blue moon. We called attention to two full moons in January, and it's going to happen again this month on the 2^nd and 31^st. However, this definition is rather new, and the occurrence is not all that rare. Our Moon orbits the Earth every 28 days; this is its sidereal period, which means "measured with respect to the stars." However, because of Earth's motion about the Sun, the relative position of Sun and Moon in the sky repeats only every 29 days or so, this is its solar period, which more nearly matches the length of a typical month. Indeed, the word "month" shares a common root with "moon." This is the interval between full moons. Any month other than February in which a full moon occurs on the 1^st or 2^nd can have a second full moon. It seems rare, because the day of the month of a full moon drifts slowly thought the calendar, due to the mismatch between the length of a typical month and the solar period. The next time we see two blue moons in a single year will be in January and March of 2018.

Another way to get a blue moon is for a volcanic eruption to throw dust high into the atmosphere. Dust will selectively scatter red light, leaving to the moon's appearance more of a blue tint. This is probably the original meaning of the term, since such massive eruptions are even rarer than a - dare I say it? - blue moon. They would also be virtually impossible to predict.

Lunar phases for March: The Moon is Full on the 2^nd and 31^st, occurring at 1:58 am and 5:49 pm, respectively. Last quarter will be on the 10^th and 3:40 am; New Moon arrives at 1:48 pm on the 17^th; and first quarter occurs on the 24^th at 5:18 am.

The planets give a brilliant show at sunset for the first half of the month. Jupiter is diving into the twilight glow by mid-month, but Venus is climbing higher throughout the month. Saturn trails Venus at the beginning of the month, but will be about 13 degrees below it by month's end.

Looking overhead at 9:00 pm at mid-month, we find the bright twins Castor and Pollux a bet west of zenith. Sweeping to the south, we see bright stars Procyon in Canis Minor and brilliant Sirius in Canis Major. To the southwest, the sky is dominated by Orion's distinctive pattern. Directly above the western horizon is Aldebaran, in Taurus, with the Pleiades just to the right. To the north, the inverted "Big Dipper" of Ursa Major is approaching its highest point. The two stars at the end of the "bowl" are called pointers, because a line through them extended to the north leads us to the pole star, Polaris. It's not directly over the pole, but it's close enough to make it a useful navigation aid in the northern hemisphere, since it never sets below the horizon from that vantage.

Looking to the east, we see two bright stars just coming above the horizon - Arcturus is the bright one on the left, with Spica to the right. Above Spica we find the constellation Leo, with its distinctive scythe shaped "head" and the bright star Regulus at the heart of the lion.