May 1996

by Steve Stefanik

The month of May began in the glow of the full moon unlike last month when the full moon rose in total lunar eclipse. There won’t be another naked-eye comet like Hyakutake this month either, not until comet Hale-Bopp arrives this time next year.

The planet Mercury is just below the open star cluster Pleiades low on the northwestern horizon after sunset. It may be difficult to locate because its only +1.6 magnitude and you have to have a clear unobstructed view to see it. If you have difficulty locating it, the brilliant planet Venus is above and to the left of it. Mercury disappears behind the sun by mid-month leaving Venus the lone beacon to light the night sky, literally! Its so bright at magnitude -4.5 that if you live in a dark area you may see your own shadow against something light in color later in the month when the moon is not out.

You may also notice that Venus is very high in the sky well into the night (setting after 11:00 p.m. EDT) more than 30 degrees from the western horizon where it customarily lurks as the "evening star". The reason for this is because its 225 day orbit is tilted 3.4 degrees from ours. It goes through a 584 day cycle from a "morning star" to an "evening star". Every five Venus cycles mesh with our 365-day calendar every eight years. As a result Venus is at its highest altitude and sets furthest north in this century tonight! By the end of the month it will be only 5 degrees above the western horizon by 9:00 p.m.

By midnight some of the familiar stars of summer begin rising. Vega in the constellation Lyra replaces Sirius as the brightest star in the northern hemisphere sky. Deneb in the constellation Cygnus and Altair in the constellation Aquilla complete the "Summer Triangle". Antares the red star in Scorpio and the planet Jupiter is in the constellation Sagittarius not far behind.

Uranus at +5.7 magnitude and Neptune at +7.9 magnitude are on the border between Sagittarius and Capricorn but you’ll need powerful binoculars to see them or wait until this summer when they reach opposition in July.

Pluto is on the nearby Scorpius-Ophiuchus border but can’t be seen without a powerful telescope of course.

Saturn also returns to the predawn sky this month in the constellation Pisces where it will return to summertime dominance. The rings will once again be visible after being on edge much of last year.

Mercury will join Mars in the morning sky by month’s end although the pair will be difficult to spot in the early morning twilight but you might be able to spot them with binoculars.