To the reader:
The Skywatcher's Diary for April 2001 has been prepared by
David Batch. Credit to the author and to
Abrams Planetarium,
Department of Physics and Astronomy at
Michigan State University, and mention of
our
Sky Calendar, would be
appreciated.
A sample issue of the Sky Calendar is available over the Internet. It
can be viewed via the World-Wide Web at
http://www.pa.msu.edu/abrams/SkyCalendar/Index.html
If you would like a printed sample of the April issue, please send a long,
self-addressed stamped envelope to:
April Sky Calendar
Abrams Planetarium
Michigan State University
East Lansing, MI 48824
Each month, the Department of Physics and Astronomy at Michigan State
University makes the Skywatcher's Diary available over the Internet. It can
be accessed at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Diary.html
Current and back-issues of the Skywatcher's Diary are available in our
archives
at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Archives.html
ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: April 2001
Daylight Saving Time begins today, the earliest date possible. By law, the hour between 2 a.m. and 3 a.m. does not exist. At nightfall the First Quarter Moon appears high in the SSW. Notice the Gemini brothers above the Moon. Pollux, the brighter and lower twin, is 7 degrees (less than a fist width) away. Castor is another 3 degrees higher.
The Moon lies just to the east (left) of a line drawn through the Gemini Twins this evening. Use binoculars to spy the Praesepe star cluster 3 degrees (six moon diameters) to the left of the Moon. Normally the cluster is visible without optical aid, but tonight the Moon's glare conceals the group. During the early morning hours the Moon passes through the Praesepe, covering many of the stars.
Venus has moved into the morning sky and soon will dominate the eastern dawn. Now it rises a mere 50 minutes before the sun, so viewing it requires effort and a flat horizon. Look 30 minutes before sunrise slightly to the north of due east. Binoculars will reveal a large but thin crescent shape. The planet's orbit is carrying it away from us, so the image will get smaller (and the crescent thicker) as weeks pass.
The Moon is 5 degrees (half a fist) to the lower left of the star Regulus, in Leo. The shadow of Jupiter's number two moon, Europa, crosses the planet's disk from twilight until 11:03 p.m. EDT. For a brief span, beginning at 10:48 p.m., the shadow of Jupiter's largest moon, Ganymede, joins Europa's, producing a double shadow transit. A moderate amateur telescope and clear, steady skies will be needed to capture the event.
The Moon sits below the haunches of the Leo, the Lion, marked by a right triangle of stars 7 degrees (less than a fist) to the upper left. Denebola, the lowest and brightest of the trio, punctuates the beast's tail. That star is traveling nearly parallel to our sun in its journey around the Milky Way, at a distance of 40 light years.
The star Aldebaran, bright orange eye of Taurus, the Bull, is 5 degrees (half a fist) to Jupiter's left. Pick out the fainter V-shaped group of stars, known as the Hyades, that stretch below Aldebaran. They outline the bull's face. Carefully note (or photograph) Jupiter's position relative to these stars, then do so again toward month's end. The planet's orbital motion should become obvious.
Full Moon occurs at 11:33 p.m. It is sometimes called the Easter Moon because it plays a role in figuring the date of the holiday. The standard rule quoted for Easter is "the Sunday after the first full moon on or after the Vernal Equinox." In practice the religious definitions of full moon and vernal equinox can occasionally differ from the astronomical ones. The time zone used also figures in, as is the case this year. Easter is not tomorrow but rather April 15th.
Last night the Moon hung 9 degrees (a fist width) to the upper left of Spica, the brightest star in Virgo. Tonight you will find it 11 degrees to the lower left. Look carefully to tell on which part of the Moon nightfall is beginning, that is, where the crescent shadow appears. Binoculars help.
The Big Dipper has been steadily climbing out of its winter obscurity, appearing higher each week. At nightfall it perches two-thirds of the way up in the NE and by midnight reaches almost overhead. In the E the bright star Arcturus trails the dipper. Find it by extending the dipper's handle one "dipper length" to the lower right.
The Moon rises 3 hours after sunset. By dawn tomorrow, Luna swings to the SSW. Then Antares, the ruddy star at the heart of the scorpion, can be located 9 degrees (a fist width) to the Moon's lower left. Mars, similar in appearance to Antares but brighter, is about twice as far directly to the Moon's left.
Tomorrow morning the Moon sits 8 degrees to the right (west) of Mars. If you are more likely to stay up late than get up early, the Moon rises in the SE 4 hours after sunset (half an hour after midnight), and Mars follows an hour later.
This morning the Moon is found to the right of Mars. Early this evening it will pass within 1 degree (two moon diameters) of the planet, but the event is invisible to us Ñ the pair doesn't rise until after midnight. By the time the Moon comes up in the SE it will be 3 degrees to the lower left of Mars. The two objects will drift apart another degree by dawn on Friday.
Friday the Thirteenth occurs every year 1, 2, or 3 times. This year it happens twice Ñ July is the other month. Saturn currently sets about 3 hours after the sun, and Jupiter follows an hour later. By the end of the month the Ringed Planet sets only an hour and 40 minutes after sunset. In early May, Saturn becomes lost in the twilight glare.
The Summer Triangle, that signpost of warm nights, is making its way back into the evening sky. Vega, the brightest of the three stars, rises between NE and NNE slightly more than an hour after sunset. Deneb follows 35 minutes later, 25 degrees (2 1/2 fists) to the right of Vega. The triangle isn't complete until after 1 a.m. when Altair crosses the ENE horizon.
Last Quarter Moon occurs at 11:31 a.m. EDT this Easter Sunday. It sets about an hour later near the SW. Sundial enthusiasts take note: the Equation of Time is zero today. If you are curious about keeping time by sunlight, visit the North American Sundial Society web site at http://www.sundials.org.
Venus now rises an hour and 20 minutes before sunrise, so it is no challenge if you are out at the right time. Look low in the East. The waning crescent Moon rises about an hour earlier than Venus tomorrow morning (but farther to the south) and a half hour before the planet on Monday morning. Use binoculars to examine both the crescent Moon and crescent Venus.
Spica, the brightest star in Virgo, sits 20 degrees (two fists) above the SE horizon at nightfall. It is the only 1st-magnitude star in that vicinity. Look to its right, about 20 degrees, and find Corvus, the Crow. Four 3rd-magnitude stars in the shape of a ship's mainsail are the distinguishing pattern. The top two stars point to Spica in the same way that the Big Dipper's pointer stars aim toward Polaris.
As the Earth orbits the sun, our daystar appears to pass in front of the various constellations of the zodiac. Today the sun enters the boundary of the constellation Aries, the Ram. Unlike astrology's horoscopic signs of the zodiac, no mystical properties are assigned to this passage. It is simply another (mostly historic) way of keeping track of the calendar.
An hour before sunrise the Moon and Venus appear just above the eastern horizon. The planet sits almost due east while the Moon is farther to the right, near ESE. Tomorrow morning look 40 minutes before sunrise to find the thin old Moon sitting on the horizon, 12 degrees (a fist width) to Venus' lower right.
Leo, the Lion, stands highest these evenings at the end of twilight. Regulus, the brightest star in the constellation, can be found two-thirds of the way up in the south. It punctuates the "backward question mark," a pattern of fainter stars above Regulus that represents the head of the mighty king of animals.
The Lyrid meteor shower peaks around midnight. Although generally not a spectacular display, the shower is variable and has, at times, produced as many as one meteor per minute. The almost-new Moon means dark skies all night Ñ ideal conditions. Meteors can appear anywhere in the sky, not just near Lyra, so get out in the open where you can take in the view from horizon to horizon.
Rigel, the bright star at Orion's left foot, sets at the end of twilight on this date every year for our latitude. Each night the star sets about 4 minutes earlier. Diligent observers will be able to spot Rigel for another week or two before it disappears into the sunset glow. In the coming weeks a similar fate awaits Aldebaran, Sirius, and Betelgeuse. Our ancestors were well aware of this repeating pattern of star visibility, using it as the basis for early calendars.
The Moon is New at 11:26 a.m. EDT. One way to describe New Moon is to say that the Moon is in conjunction, or rough alignment, with the sun. If the alignment is exact we witness a solar eclipse. Coincidentally, the planet Mercury is also in conjunction with the sun today, but on the backside of its orbit. Because of their proximity to the direction of the sun, neither body is visible.
The Moon returns to the evening sky. Catch the very thin crescent 9 degrees (a fist width) below Saturn, but look early Ñ about 45 minutes after sunset. Thirty minutes later Luna sets. Use binoculars to examine the crescent. You are viewing sunrise on the lunar landscape.
Photo op alert: An hour after sunset the Moon perches nearly between the two giant planets. The Moon is 5 degrees (10 moon diameters) to the upper left of Saturn and 8 degrees below Jupiter. The dark indentation seen in a modest telescope just above the middle of the crescent is a portion of the large crater known as Mare Crisium, or Sea of Crisis.
An hour after sunset the crescent Moon, Jupiter, and Saturn form an arc in the WNW. Twelve degrees (a fist) separate the planets, and the Moon is 6 degrees to the upper left of Jupiter. Small telescopes show the dark, oval Mare Crisium on the top half of the crescent.
Tonight the Moon sits in the middle of the great ellipse of seven bright stars formed from Rigel in the foot of Orion, Sirius, Procyon, the Gemini Twins, Capella, and Aldebaran in Taurus. Point a small telescope or spotting scope at the Moon to see an abundance of craters.
The crescent Moon hangs under the Gemini Twins, 9 degrees (a fist) directly below Pollux. Today is National Astronomy Day. Check to see if your local astronomy club, planetarium, or science museum is offering special activities or public observing sessions and participate.
No longer below the twins, as it was last night, the Moon is now in line with those two bright stars, 9 degrees to the left and slightly above Pollux. You will notice the Moon has not quite reached First Quarter (half moon). That event occurs at 1:08 p.m. tomorrow.
Mars has brightened noticeably from early in the month. It is now approaching its eastern "stationary" point in its orbital swing against the background stars before turning west in retrograde motion. You should develop the habit of regularly watching Mars over the next two months so you will not miss any of Mars' greatest display in 12 years.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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