The Skywatcher's Diary for April 2006 has been prepared by Robert C. Victor, formerly Staff Astronomer (now retired). 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/
At dusk find Saturn very high in SSE as April opens, drifting through S and SW as the month runs its course. Mars starts high in WSW at dusk, and ends month still high in W. Later in the evening, bright Jupiter rises in ESE within 3 hours after sunset on April 1, shifting earlier to within a quarter-hour after sunset at month's end. After Jupiter has risen, all three bright outer planets will be visible in the evening, spanning 135 degrees at midmonth.
Get outdoors by an hour before sunup, and you'll be rewarded by views of the two brightest planets, Venus in ESE, and Jupiter in SW. You can see Venus in the daytime, just by keeping track of it until sunrise. A telescope then reveals that planet just over half full in early April, becoming more full and shrinking in apparent size as it recedes from Earth. Mercury can be spotted in morning mid-twilight early in month, just above horizon about 10 degrees south of east. Binoculars help pick it out in the bright twilight glow. Look for it to lower left of Venus, by 20 degrees on April 1, and 18 degrees on April 7-13.
The Moon was New on March 29, is just past First Quarter phase by the evening April 5, Full on Apr. 13, is just past Last Quarter phase on the morning of Apr. 21, and New on Apr. 27. The Moon appears near naked-eye planets on the following dates: As a fat crescent near Mars on evening of Apr. 3; in waxing gibbous phase near Saturn on evening of Apr. 6; in waning gibbous phase near Jupiter from late evening until dawn on night of Apr. 14-15; and as a waning crescent near Venus at dawn on morning of Apr. 24.
Stars: Around nightfall throughout April, look high in the northeast for the well-known Big Dipper. Imagine its bowl to have a leaky bottom. Then the watery contents would pour onto the back of Leo the Lion, represented on our map by a Sickle (whose blade represents the mane of the Lion) and a triangle (representing the Lion's hindquarters). The star Regulus, at the handle of the Sickle, represents Leo's heart.
Extend a line connecting the Big Dipper's Pointer stars (the two stars in the front of the bowl) to point out Polaris, the North Star, always in the north. You can also use the Dipper to locate a much brighter but less well known star, Arcturus, by following the curve of the handle: "Follow the arc to Arcturus," which is shown on our map in the east. To the right of Arcturus and lower left of Leo is the constellation Virgo, half risen at the time of our map. Even at the start of April, Virgo's brightest star, Spica, has risen by nightfall and is easy to see low in the east-southeast. Find that star by extending the curve of the Big Dipper's handle on past Arcturus, and you'll "Drive a spike to Spica."
Leo and Virgo are constellations of the zodiac, the backdrop against which the Sun, Moon and planets are seen. In April we see Virgo when we face away from the Sun, and so the Moon will be in its part of the sky for a few days around Full, which occurs on April 13.
Leo is facing west, toward two bright planets and a lineup of zodiac constellations. In order westward from Leo, they are: Cancer, the Crab, containing bright Saturn and the Beehive cluster of faint stars visible in the same binocular field; Gemini, containing the bright "Twin" stars, Pollux and Castor; and Taurus, containing Mars and the similarly bright star Aldebaran marking the eye of the Bull, and two beautiful star clusters, the Hyades and the Pleiades. From about April 18 until May 14, the Sun appears against the background of the next zodiacal constellation to the west, Aries the Ram, below the map's western horizon.
The plane of the solar system or centerline of the zodiac in our April evening sky is pretty well defined by the line connecting Mars and Saturn extended toward both horizons. You'll notice that the line extended eastward beyond Saturn passes quite close to Regulus, then farther on to Spica low in the ESE. The Twin stars Pollux and Castor, between Mars and Saturn, lie a little north of the line, while Aldebaran, in the western sky, is a bit south of the Saturn to Mars line extended. Orion and the two bright Dog Stars Sirius and Procyon following him across the sky are well south of the plane, while the Mother Goat star Capella and the Bear-chaser star Arcturus lie well to the north.
A comet (not orbiting in the plane of the planetary orbits) may be visible in binoculars late this month and in May. See information and web links under April 30 and May 1 in the Diary below.
Following is a day-by-day guide to celestial happenings during April 2006. For drawings of many of these events, and an evening sky map, request a free sample copy of the Abrams Planetarium Sky Calendar by sending a self-addressed, stamped envelope to Sample Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824. Or you can subscribe for $11 per year. We appreciate your subscriptions!
Observers in eastern parts of U.S. and Canada are ideally placed to observe the Moon occult or cover several stars of the Pleiades cluster early this evening. From East Lansing, MI the cluster's brightest member, 3rd-mag. Alcyone or Eta Tauri is covered by the leading dark edge of the Moon at 7:43 p.m., in bright twilight. Later, Atlas or 27 Tauri, at mag. 3.6 the second-brightest member, is covered by the visible earthlit leading edge at 8:33 p.m., and Alcyone reappears at the Moon's sunlit edge at 8:48 p.m. From a narrow path crossing through Miami, Florida, mountains along the Moon's southern edge will cover and uncover Alcyone in a "grazing occultation" for a few minutes around 8:34 p.m. EST. Times of events and the list of stars which are hidden vary with location, but wherever you are in the East, the view through telescopes and binoculars should be spectacular! Even in the far West, where the occultations occur before sunset, folks will have a striking view of the crescent Moon just above the Pleiades as the sky darkens. For details, go to the web site of the International Occultation Timing Association:
http://www.lunar-occultations.com/iota
Compared to last night, the sky gets dark an hour later by your clocks, which should now be set an hour ahead for daylight saving time. An hour after sunset on Sunday, the Moon's change in position from the previous night will be obvious. Tonight, the Moon is much higher than the Pleiades cluster. The reddish star 11 degrees lower left of the Moon is Aldebaran, eye of Taurus, the Bull. Mars, another red "star" but shining more steadily than Aldebaran, is about the same distance to Moon's upper left. Also on Sunday, note on either side of Mars the two fainter stars marking the tips of the Bull's horns, all three lying in a straight line. Check the position of Mars on subsequent nights to detect its motion, amounting to just over one apparent Moon's width per day.
About one-and-a-half hours before sunset, this month's northernmost Moon passes not far south of overhead. It's a fat crescent, now about one-third full. An hour after sunset, it's still high in the west, with Mars to its lower left and the star Elnath or Beta Tauri to its lower left, forming a nearly equilateral triangle 4 degrees on a side as seen from mid-U.S. You should be able to easily fit both Moon and Mars in same 7-power binocular field.
At nightfall, very high in the western sky, you'll find the moon almost half full (nearing First Quarter phase when it's 90 degrees or one-quarter circle from the Sun). Because of the low angle of solar illumination on the lunar landscape, this is the best phase to see lunar surface detail through binoculars and telescopes. Also on Tuesday evening, note Mars 15 degrees to Moon's lower right and the Gemini twins, Pollux and Castor, not quite as far above the Moon, and Saturn, 25 degrees to Moon's upper left.
About 1-1/2 hours after sunset, note Pollux about 2 degrees upper right of the Moon, now just over half full. Castor, the other Twin, is 4-1/2 degrees upper right of Pollux. Around 11 p.m. EDT from lower Michigan, the Moon's northern edge glides within 2 degrees south of Pollux, the brighter of the Gemini Twins. Note bright steady Saturn 13 degrees to the Moon's upper left.
The waxing gibbous moon, two-thirds full, is very high in SSW at nightfall and is accompanied by Saturn within 4 degrees below. Moon and Saturn appear closest about 11:30 p.m. EDT in lower Michigan. In early April, Saturn's rings are tipped 20 degrees from edge-on, the best for many years to come. And sunlight now from a direction different from our line of sight causes the planet to cast a noticeable shadow on the rings, resulting in an especially 3-D appearance. So be sure to take the opportunity to view Saturn through a telescope!
As the Moon approaches full, it will slip past two additional bright stars of the zodiac. Can you find them? At nightfall, Moon is very high, just east of S, with Saturn 13ø to right, and Regulus, heart of Leo, about same distance lower left.
At nightfall, the Moon is high in SSE, with Regulus 2 or 3 degrees below. From mid-Michigan, closest approach will occur shortly after 2 a.m., when the Moon will pass just less than two degrees north of Regulus, the heart of Leo, the Lion.
At nightfall, the Moon is well up in SE, with Regulus 11 degrees upper right, and Spica low in ESE 43 degrees to Moon's lower left. Watch the Moon approach the latter star the next three evenings.
The Moon is in the southeast at nightfall, nearly halfway toward overhead. Note Regulus 23 degrees to Moon's upper right, and Spica 31 degrees to Moon's lower left.
At nightfall, Moon is in southeast, about one-third of the way toward overhead. Note Spica 19 degrees to Moon's lower left.
Half an hour before sunset, look for the rising, nearly full Moon barely above the horizon between E and ESE. At nightfall, look for Spica, the spike of grain in the hand of Virgo, 7 degrees to Moon's lower left. Tonight, Spica is at opposition. Each year around April 12-13, as we look toward Spica, we are facing outward in our solar system, directly away from the sun. It's only a coincidence that the full "Egg Moon" (the first full moon of spring, or Easter Full Moon) happens on April 13 this year. Spica is up all night, rising at sunset, reaching its highest, due south, in the middle of the night (1:38 a.m. EDT in East Lansing, MI), and setting in WSW around sunrise. At dawn's first light on Thursday, look for Spica just 4 degrees to Moon's upper left.
The Moon, now just past full, rises in ESE within half an hour after sunset. As the sky darkens, look for Spica 5 degrees to Moon's upper right, and bright Arcturus in east, 34 degrees to Moon's upper left. Use the handle of the Big Dipper to "Follow the arc to Arcturus, and drive a spike to Spica."
About two hours after sunset, look for Jupiter within 7 degrees lower left of the Moon. One hour before sunup on Saturday, the Moon will be in the SW with Jupiter 6 degrees above. Venus will be low in ESE.
About three hours after sunset, look for the Moon very low, about 25 degrees south of east, about 10 degrees below bright Jupiter. Using binoculars, look for a double star, magnitudes 3 and 5, just 4 arcminutes apart, within 1-1/2 degrees upper right of Jupiter. On April 24, Jupiter will pass just one degree north of that star.
An hour before sunrise on Sunday, the Moon is low in SSW to SW. Jupiter is 13 degrees to Moon's upper right, and Antares is 12 degrees to Moon's upper left. Venus is low in ESE.
Tonight four hours after sunset, look for the waning gibbous Moon just risen in SE, about 23 degrees lower left of Jupiter. As Moon rises higher, use binoculars to see Antares very closely lower left of Moon. Closest approach from Michigan occurs shortly before 4 a.m. EDT on Monday morning. About an hour before sunrise, Moon is low in SSW with Antares about one degree from the Moon's edge. Jupiter is in SW, and Venus very low in E to ESE.
Look for April's southernmost Moons on Tuesday and Wednesday mornings. From East Lansing, MI on Tuesday morning, the waning gibbous Moon passes due south, only 18 degrees up, at 5:23 a.m. EDT, in early twilight. There and elsewhere at the same latitude, the time is nearly 1-1/2 hours before local sunrise. (From locations farther south, the Sun rises later and the Moon reaches its high point in S farther ahead of sunrise, but higher in the sky.)
Antares will be within 14 degrees to the right of the Moon, and the Teapot of Sagittarius, consisting of eight stars of the 2nd and 3rd magnitude, lies 8 to 21 degrees left of the Moon. On Wednesday morning at this same time, the Moon will be inside the Teapot and about one hour before it reaches due south. On Tuesday morning, aim binoculars at Venus before the sky gets too bright, and look for the 4th-mag. star Lambda Aquarii 1.6 degrees upper right of Venus, and 6th-mag. Uranus 0.3 degree to Venus' lower right. This sighting would be difficult from northern states, where the tight trio rises after twilight begins.
If you look on Wednesday morning, 1-1/2 hours before sunrise, you can see Moon in SSE, inside the Teapot of Sagittarius. Jupiter is in SW, and Antares lies about midway between Moon and Jupiter. In East Lansing, MI the Moon passes due south, only 18 degrees up, at 6:22 a.m. EDT (28 minutes before sunrise).
For the next several evenings, carefully observe the position of Mars in relation to the background stars of Gemini. Look high in the west at nightfall, and you'll see tonight that Mars is 2.5 degrees north of a 3rd-mag. star, Eta in Gemini, marking Castor's toe. In three nights, on Sat. Apr. 22, Mars will pass the same distance north of a similar star, Mu Geminorum, marking Castor's heel. Mars is moving nearly 0.6 degree per day eastward against the stars, and on Apr. 30 it will pass only 0.5 degree south of another 3rd-mag. star, Epsilon in Gemini. On May 22 and 23, Mars will finally pass 5 degrees south of Pollux, Gemini's brightest star. Look nightly! Binoculars give wonderful views.
If you get up an hour before sunup on Thursday, note that the Moon has traveled more than half the distance from Jupiter to Venus.
On Friday morning, an hour before sunrise, the Moon has passed Last Quarter phase and is just under half full. Jupiter is low in SW, and Venus is even lower in E to ESE. The Moon has traveled nearly two-thirds of the way from Jupiter toward Venus.
Get outside in predawn darkness hours to watch for Lyrid meteors. And if you're up before first light for the next several mornings, watch Jupiter pass one degree north of the 3rd-mag. star Alpha in Libra. (Binoculars show Alpha has a close 5th-mag. companion.)
As the sky brightens Saturday morning, look for Venus nearly 30 degrees to the crescent Moon's lower left.
This is the evening Mars passes 2.5 degrees north of Mu Gem, Castor's heel.
Our May Sky Calendar and May Evening Skies star chart are available on the web, at
http://www.pa.msu.edu/abrams/skycalendar
If you are planning to host events for National Astronomy Day, Saturday, May 6, we encourage you to reprint copies for free distribution to those who attend.
An hour before sunup on Sunday, look low in ESE to find Venus 16 degrees lower left of a crescent Moon, about one-quarter full.
Get up at least 1-1/2 hours before sunup on Monday to watch for the rising of the crescent Moon and Venus. They are within 3 degrees apart, and are getting even closer with each quarter hour. This is the best Moon-Venus conjunction this year. Look also for Jupiter in SW, and just one degree above it, the 3rd-mag. Alpha Librae, also called Zubeneschamali, the Southern Claw (of an earlier, larger version of the Scorpion).
Our faster-moving Earth is now heading in the direction just below the head of Capricornus, in the southeast. Jupiter is heading in approximately the same direction, but more slowly. As a result, Jupiter in coming mornings will seem to shift to the right (west) relative to the star Alpha Librae, even though it is actually moving toward the left (east). This apparent motion, called retrograde, results from our faster-moving Earth overtakes Jupiter. This apparent motion of Jupiter will continue until July 6 (two months after Jupiter's opposition, when we overtake it). Jupiter will then appear over 6 degrees west of Alpha. And you won't have to get up early to see it. Jupiter and Alpha Lib will then appear in the evening sky!
Back to Monday morning, with Venus so close to the Moon, see how long you can follow them into daylight. They'll approach each other until well past sunrise. In East Lansing, MI, sunrise is at 6:43 a.m. EDT (when Venus and Moon are within 2 degrees apart). They're nearly halfway up in south just before 11 a.m. EDT, and a few minutes later appear closest as the northern cusp of the lunar crescent passes just 0.8 degree (about 1-1/2 moon-widths) to the south of Venus.
Go out around 1-1/2 hours after sunset, when the sky has become quite dark. Our orbital motion around the Sun is now directed away from Saturn, which is high in the SW to WSW, to upper left of the Twin stars, Pollux and Castor. Look for bright Jupiter very low in ESE, with Spica to its upper right. Waiting until later in the evening if necessary, when they're higher, look for the star Alpha Librae one degree to the south (right) of Jupiter. We passed Spica April 12-13, and will overtake Jupiter on May 4. If we look directly away from the Sun tonight, look about halfway from Spica toward Jupiter. Knowing which way the Earth (and Jupiter) are moving in space, can you visualize which way Jupiter will appear to move relative to Alpha Lib in coming nights?
Get up an hour before sunrise on Tuesday to catch the thin crescent Moon just rising in the east, within 12 degrees lower left of Venus.
Last chance to see the old Moon: On Wednesday morning, 30 minutes before sunrise, look very low, 8 degrees north of east, to see a very thin crescent Moon, 3 percent full and 25 degrees lower left of Venus. Even though twilight is bright, you can still see Jupiter, low between SW and WSW.
About 1-1/2 hours after sunset, Orion's belt and bright shoulder Betelgeuse are still visible, low a little S of W, but they set 4 minutes earlier each evening. Rigel, marking Orion's foot, below the belt, is just setting, so you must look earlier. About one hour after sunset would be a good time to look. The brightest star, Sirius, is low in SW to WSW - find it by extending Orion's belt to the left. High above Sirius and below Saturn, forming a nearly equilateral triangle with Sirius and Betelgeuse, is Procyon, the Little Dog Star. Extend Orion's belt to the right to find Aldebaran, eye of Taurus, and beyond to the Pleiades cluster. As Earth orbits around the Sun, these stars appear lower each evening and will soon disappear. I really enjoy following the seasonal changes in the evening sky at this time of year, when there are so many bright star "markers" in the west. You can really see the results of the Earth's motion around the Sun! Around May 20, the Sun will appear to pass the Pleiades, and long before then (quite soon, actually), they will be gone.
New Moon occurs at 3:44 p.m. today. The Moon is not visible today. Check again tomorrow evening!
An hour after sunset, the thin crescent young Moon is very low in WNW. (I recommend you start looking for it earlier.) Using binoculars if necessary, look for the Pleiades about 6 degrees to Moon's upper left, and Aldebaran 14 degrees upper left of the Pleiades and 18 degrees upper left of the Moon.
An hour after sunset, the 6 percent crescent Moon is easy to see low in WNW. Note beautiful earthshine on its dark side, and, using binoculars for a better view, look for the compact dipper-shaped Pleiades star cluster 8 degrees to Moon's lower right, and Aldebaran and the V-shaped Hyades cluster within 10 degrees to Moon's lower left. Find Mars in west about 31 degrees to Moon's upper left, then note the alignment of the four solar system bodies: Moon low in WNW; Mars well up in W; Saturn high in SW to WSW; and Jupiter low in ESE.
An hour after sunset, find the crescent Moon between W and WNW, with Mars 18 degrees to its upper left. As the sky darkens, you'll see that both objects are passing close to a star tonight. Mars is 0.5 degree (about a moon's width) S of the 3rd-mag. star Epsilon in Gemini. The Moon is also passing just south of a star, the 1.7-mag. star Beta in Taurus, marking the Bull's northern horn. From East Lansing, MI around 11 p.m. EDT, the Moon's northern cusp (point of the crescent) clears the star by just over a moon's width. Look again tomorrow evening to check on the relative progress of the Moon and Mars after 24 hours.
COMET 73P/Schwassmann-Wachmann 3 split into fragments during its last two apparitions, and has recently been breaking up into still smaller pieces. Component C is the largest and brightest fragment. Tonight and Monday night, binoculars may show this comet's C-component (at mag. 5?) within the southern end of the Keystone of Hercules. On night of May 7-8, it will appear (at mag. 4?) between Beta and Gamma Lyrae, the pair of 3rd-mag. stars 2 degrees apart at the south end of the parallelogram of Lyra, some 6 to 7.5 degrees SSE of Vega. After passing through the Summer Triangle, the comet fragment comes within 0.08 a.u. (about 7 million miles) of Earth on May 12, but will likely be no brighter than mag. 3.5 at best, in a bright moonlit sky. For web links to a finder chart and updates on the comet, visit these web sites:
Includes finder chart and graph of the comet's brightness:
http://www.aerith.net/comet/catalog/0073P/2006.html
Includes reports of observations, with magnitude estimates:
http://www.cometobservation.com
NASA press releases:
http://science.nasa.gov/headlines/y2006/24mar_73p.htm
http://science.nasa.gov/headlines
JPL Ephemeris generator for solar system bodies:
http://ssd.jpl.nasa.gov/horizons.cgi
Finally, our May star chart this year is the more detailed version, and shows the Keystone of Hercules and the parallelogram of Lyra, (where the comet is located on April 30-May 1 and on the night of May 7) and is accompanied by the May Sky Calendar:
http://www.pa.msu.edu/abrams/skycalendar
Moon farthest north tonight and May 28. Tonight binoculars may show Comet Schwassmann-Wachmann 3 (mag. 5?) near lower corner of Keystone of Hercules. Evenings this week, watch the Moon pass Mars, Castor and Pollux, Saturn, and Regulus.
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Please send any comments, suggestions, or questions to Thomas G. Ferguson: fergus52@msu.edu |