StarWatch: Moravian College Astronomy
StarWatch for the greater Lehigh Valley

MARCH  1998

079a  MARCH 1-4, 1998:   Occultation of Aldebaran
You may recall the close encounter that Saturn experienced last November 11, when the moon slid under the Ringed World. It was a beautiful sight amidst the scudding clouds of a late, warm autumn evening. This Wednesday, Aldebaran, the reddish eye of Taurus, the Bull, is posed for a direct "hit" when it passes behind the Queen of the Night at approximately 7:35 p.m. Unlike the Saturn observations, where the moon was nearly full and extremely bright, the moon, this time, is a fat crescent and far less obtrusive. Aldebaran, the 13th brightest star of the night, is also occulted against the moonís unlit surface. This will simplify observations through telescopes and binoculars by making Aldebaran much easier to spot. The Mid-Atlantic and Northeast will have the best vantage points because it will be completely dark throughout the entire event. Aldebaran reappears from behind the sun-washed surface of the moon approximately 50 minutes later, about 8:25 p.m. If you would like to watch this event unfold, start observing the crescent moon tonight and watch as it moves towards Aldebaran over the next several evenings. Bright Aldebaran can be located by following the line created by the three belt stars of Orion, the Hunter. Continue upward along this path about 2-1/2 clenched fist widths. Start observing at least one-half hour before Aldebaran is occulted.
079b  MARCH 5-6, 1998:   Finger Angles
When people try to explain the separation between objects in the sky, they often use terms like, "they were about two inches apart." This is very common for UFO sightings because most of these observations are make by individuals with little or no training in sky observations. The heavens are considered to be a dome over our heads, and as such, distances measured between stars or the heights of objects above the horizon must be measured as angles. There are 90 degrees between the horizon and the zenith, the point directly overhead, and 360 degrees around the horizon circle, which is where the sky "touches" the Earth. The hand and various fingers held at armís length are marvelous tools for measuring angular separations. The index finger covers about 1 degree of sky, while the entire fist when held in a clenched (fighting) position covers about 10 degrees. Use the index, middle, and fourth fingers to hide about 5 degrees of sky, while the pinkie and thumb spread to their maximum extent reach across 25 degrees of the heavens. The index and pinkie fingers span about 15 degrees. That last one, I still canít perform well, nor can I make the famous Vulcan "V" with the index/middle fingers separated from the fourth and pinkie. Enough of this finger manipulation, Iím getting a bit nervous. More about this in two weeks.
080    MARCH 8, 1998:   Venus Ablaze
With the full moon occurring on Friday, the 13th, the landscape and sky will be flooded with light. It is once again time to focus upon other bright celestial objects. The best of them all is the planet Venus, third brightest object in the sky, after the sun and the moon. Last December, Venus was a striking object in the early evening sky, becoming visible even before sunset, if you knew just where to look. Venus was to the east of the sun. Then Venus disappeared as its orbital motions carried it between the Earth and sun to reemerge in the morning sky, west of Sol. By early February, it was ablaze in the southeast through leafless trees as I helped carry my wifeís book crate to the car, prior to her 6:45 a.m. pilgrimage to school. Venusís western elongation (distance) from the sun has now increased so that the planet rises about 4 a.m., over two hours before the sun appears. If you want to see Venus and understand why the ancients called her the goddess of beauty, check her out about 5:45 a.m. low in the east, southeast, a dazzling beacon of reflected sunlight. A partial penumbral lunar eclipse also occurs on Thursday, the 12th. Maximum immersion happens at 11:20 p.m. From certain parts of the moon, one would see the Earth hiding upwards of one half of the sunís disk. However, from the Earth, youíll basically be unaware that anything is happening.
081    MARCH 15, 1998:   Dipper Angles
Two weeks ago, I spoke about using your hand and fingers as angle measuring devices. The separations between celestial bodies in the sky are all measured as angles, not as a linear distances. At armís length your index finger equals 1 degree; a clenched fist is 10 degrees; index, middle, and fourth fingers 5 degrees; while your pinkie and index fingers spread wide is 15 degrees; pinkie and thumb extended, 25 degrees. The stars of the Big Dipper, now visible in the northeast during the early evening hours, can be used to provide us with a "hands on" experience. The Dipperís position at 7:30 p.m. is handle down, bowl up. Letís number the stars of the Dipper starting with the lowest of the handle stars as one. Following the arc of the handle to the bowl and upward to the two pointer stars finishes the count at seven. Now we are ready to examine how handy our hands really can be. The angular separation between stars 1 and 7 is 25 degrees, between stars 3 and 7, 15 degrees, and between stars 4 and 7, 10 degrees. The pointer stars, 6 and 7, which lead you to the North Star are separated by 10 degrees. The angular measure between star 7 of the Dipper and the North Star is 28 degrees, a little more than the span between your pinkie and thumb spread wide. Be sure to take off your gloves to increase your accuracy and to experience some of the true joys of late winter observing.
082    MARCH 22, 1998:   Dipper Directions
If you are a weekly reader of this column, then you know that the sky talk lately has been about the Big Dipper. It is such a handy grouping of stars. Last Friday, at 2:55 p.m. the sun crossed the celestial equator and spring was sprung. For the week surrounding the Vernal Equinox, the rising and setting positions of the sun are almost due east and west respectively. They are good locations to know since we spend so much time navigating around in our cars. The Big Dipper can also provide you with a similar homing capability at night. Presently, high in the northeast after evening twilight, the two pointer stars (top of the bowl) lead you left to the North Star. Extending a line segment from the Pole Star to the horizon points you directly north. Now make a quarter turn to the right (clockwise) and youíre looking east; another quarter turn, south; another quarter turn west; and a final quarter turn to return to north. Keep in mind the mnemonic device, "North never Eats Soggy Waffles." Thatís what I did when I got lost on the first date with the woman whom I was destined to marry. Disoriented and nervous, I pulled over on a dark deserted road to get my bearings. Thank goodness, it was clear with the Dipper and North Star plainly visible, or who knows what "direction" my life would have taken! She was duly impressed with my navigational expertise, and I knew the second date was in the bag!
083    MARCH 29, 1998:   Whirling Sky
The Big Dipper is high in the northeast during the earliest part of evening, with its two uppermost pointer stars in the bowl leading you downward and to the left, to the North Star or Polaris, nearly midway up in the sky. Its location is less than one degree from the true position where the Earthís axis points, the true position about which the sky wheels. This makes the position on the horizon directly beneath the North Star an excellent indicator of the true direction north. Note the location of the Pole Star and the other stars around it. Then go out several hours later and observe how the sky has changed, everything circling slowly around Polaris. This effect is created by the rotation (spinning) of the Earth on its axis. You can create the same illusion by simply leaning back and fixing your gaze on any bright star nearly overhead. Your body is now the Earth, and the star overhead is the location to which your axis points. Spin slowly, and note how all of the other stars pinwheel around it, creating the same circular motion that is evident in the sky. Just be careful when you straighten up. The first time I demonstrated this lesson with my students in the darkness of the planetarium, I became disoriented. Unable to tell up from down, I immediately "fell" victim to the force of gravity. Needless to say my students were highly amused by my "crash and burn" acrobatics. The lesson, however, was a smashing success.
March Star Map