StarWatch: Moravian College Astronomy
JUNE STAR MAP |
JUNE 6, 1999: Orion and the Scorpion
- Orion was a tireless hunter, making a name for himself wherever he went. He was a giant of a man, but endowed with little common sense. This naturally got himself into numerous situations which caused him great strife. His problems usually centered around women, but his demise involved boasting that no animal could kill him. Hera, the jealous wife of king Zeus, became so annoyed at Orionís bragging that she sent a small scorpion to lie in wait along one of Orionís favorite hunting trails. He was stung in his only vulnerable spot, his heel, and died. At the urging of Diana, goddess of the hunt and the moon, Zeus placed the greatest of all hunters in the sky. But that angered Hera, who made a scene, arguing that the scorpion should also be honored, since it had killed the Hunter. Zeus begrudgingly consented, but forced Hera to compromise, so that Orion would never have to face the Scorpion again. Zeus placed the two constellation figures opposite to each other so that when Orion set, the Scorpion would rise. Scorpius is a beautiful constellation with its hooked-shaped body that curls perfectly into a stinger. Unfortunately, to see it, you need a very good southern horizon free from obstructions and light pollution. Thatís difficult to find around here. However, Antares, its brightest star, is easy to spot. By 10 p.m., look for red Antares low in the southeast, about one and one half fists above the horizon. The Scorpion is due south by midnight, but Antares is still only two fists above the horizon. Notice bright Ares, Greek for the war god Mars, to the right of Antares. Antares means "the rival of Ares." The two will be close to each other by mid-September.
JUNE 13, 1999: The Beehive
- One of the showpieces of our nighttime sky, the Beehive cluster is very close to Venus this week. Observe with binoculars in the west about 9:45 p.m. The week begins with Venus less than one degree away. Each night, Venus will move more to the right of the cluster, but it will still be only five degrees away by the weekend. The Beehive is an open cluster, a grouping of stars born at the same time, and delineating a region in our galaxy that was once abundant enough in hydrogen to have formed stars. Through a small telescope, its stars hang motionless like the captured image of a swarm of bees hovering around a disturbed hive. Unlike the Pleiades of fall and winter, which reveals its youth by counting numerous blue-white stars as members, the luminaries of the Beehive appear more yellowish like our sun. The Pleiades are only 50-100 million years in age, while the Beehive is probably closer to 400 million years old. Above and to the right, and due left of the Beehive will be two brighter stars, Gamma and Delta Cancri (in Cancer, the Crab). These two stars have been called the "asses" with the cluster acting as a manger. Manger in Latin is "praesepe," thus giving this grouping yet another name. The Praesepe was also the 44th object noted in Charles Messierís catalog of nonstellar objects. Messier was an 18th century French comet hunter who didnít want the embarrassment of mistaking a fixed object for a new comet. Many stargazers simply call the Beehive, M44. On Wednesday, look for the thin waxing crescent moon, Venus, and the Beehive to form an impressive equilateral triangle. Observe with binoculars, low in the west about 9:45 p.m.
JUNE 20, 1999: Summer Begins
- Monday at 3:50 p.m. marks the summer solstice, the longest day of the year. For the Lehigh Valley the sun will be above the horizon for just over 15 hours. Itís all downhill from here until we reach the winter solstice early on December 22 with slightly over 9 hours of sunlight. This week is an interesting one for watching planets, bright stars, and the moon moving among them. If youíre using binoculars and have a good western horizon, you will have an excellent opportunity for viewing illusive Mercury. Observe WNW at 9:30 p.m., and look for Caster and Pollux of the Gemini Twins a little over one binocular field above the horizon. Mercury will be over two times brighter than Pollux, the brightest star of the Twins. The week begins with Mercury about a half of a binocular field below and slightly left of Pollux. By Saturday, Mercury is in line with Caster and Pollux and about twice their distance to the left. Much easier to view will be the moonís progression across the sky. The week starts with the moon at first quarter, half illuminated as seen from Earth. It will shine far to the left of brilliant Venus and Mercury. Monday sees the waxing gibbous moon to the right of the star Spica which is now coupled with bright Mars. Tuesday, the moon has moved slightly to the left and above the pair. On Wednesday and Thursday the intensifying moon seems to move across a no manís land of sky lowering in altitude as it approaches Antares, the brightest star of the Scorpion. By Friday the moon is one fist above and to the right of Antares. The following evening, the moon has traveled about the same distance to the left of this red supergiant star. Good viewing!
JUNE 27, 1999: Moon Months: Synodic vs. Sidereal
- The moon is full tomorrow at 5:37 p.m. Even if you casually observe the cycles of the moon, you have probably realized that it was the lunar phase period that gave us the month (moonth). The moon takes approximately 29.5 days to conclude its cycle of phases, a time interval known as the synodic month. Most of us learned incorrectly in school that it took the moon 28 days to complete both its phase cycle and orbit once around the Earth. This would be nearly true (27.3 days) if the Earth were not in motion around the sun. But it does move! And as we orbit the sun, the sun changes its position against the background of stars in the sky, so that after the completion of one lunar orbit, (27.3 days) the Earth, moon, and sun are not exactly in the same alignment with each other. If we started with a new moon--Earth, moon, sun--after 27.3 days, the moon would be a thin waning crescent in the morning sky, even though it had completed one orbit around our planet. It is necessary to give the moon an additional time interval of approximately 2.2 days to catch up and repeat the same new moon phase. Thus the lunar phase period is 29.5 days on the average. But as you might suspect, this period is not uniform either. As the Earth revolves around the sun, its distance and orbital speed vary. The Earth will be farthest from the sun on July 6 and therefore moving at its slowest velocity. This will allow the moon to complete its phase period sooner. The current synodic month (new moon to new moon) will last 29.31 days. When the Earth was closest to the sun on January 3 of this year and orbiting at its highest velocity, it took the moon 29.71 days to complete a phase or synodic cycle.