To the reader:
The Skywatcher's Diary for April 1999 has been prepared by
Robert C. Victor. 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
To commemorate Astronomy Day, Saturday, May 22, our May Sky Calendar will be available to reprint for free distribution during that month. To download a copy, check our website after mid-April, or if you would like a printed sample of the May Sky Calendar, send a long, self-addressed stamped envelope to:
May 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/
Three evening planets: (1) Venus, brilliant in west at dusk, sets about 3 to 3-1/2 hours after sunset (as seen from latitude 40 degrees N). Watch Venus pass within 3 degrees south of the Pleiades April 11 and 12, and 7 degrees north of Aldebaran April 19 and 20. (2) Saturn is 14 degrees below Venus on Apr. 1 and 1 degree farther below it each day, and sinks into bright twilight by midmonth. (3) Mars rises in ESE soon after nightfall in first week, then progressively earlier in twilight next two weeks. Brightening spectacularly from magnitude -1.1 on April 1 to -1.7 when at opposition and all-night visibility on April 24, Mars retrogrades (moves west) 9 degrees in April, ending month within 8.5 degrees E of Spica. Mars is closest on May 1, at a distance of 0.578 a.u. (53.8 million miles) from Earth. Moon passes near planets on night of Apr. 2-3; evenings of Apr. 16 and 18; and nights of Apr. 28-29 and 29-30.
Morning planets: Mars at dawn is brightest "star", in SW at start of April, lowering into WSW as month progresses. Mercury brightens from mag +1 on Apr. 6 to 0 on Apr 27, but remains less than 2 degrees up in midtwilight at lat 40 degrees N. Jupiter, in conjunction with Sun on Apr. 1, emerges at month's end.
Skywatcher's Diary: April 1999
The Moon, one day past Full this evening, rises in twilight within 10 degrees south of east, about 45 minutes to an hour after sunset from the contiguous 48 states and Hawaii. Look for golden zero-magnitude Arcturus within 27 degrees to Moon's upper left. By two hours after sunset, first-magnitude Spica is easily seen 6 degrees to the Moon's right. Another hour later, bright Mars appears low in ESE, within 18 degrees lower left of Spica and some 15 degrees to Moon's lower left. For the rest of the night Mars, Spica, and Arcturus form a large isosceles triangle, with Arcturus at the apex, 33 degrees from Mars and Spica. The Moon is within the triangle. By an hour before sunup on Friday, Mars is in SW, about 12 degrees to Moon's left, while Spica is in WSW, 7 or 8 degrees to Moon's lower right.
In the western sky an hour after sunset, brilliant Venus is flanked by Saturn 15 degrees below and the Pleiades star cluster nearly 12 degrees above. The three objects lie in a straight, nearly vertical line. First- magnitude Aldebaran, eye of Taurus, lies 14 degrees upper left of the Pleiades. Look nightly for the next two weeks, and watch Venus pass the Pleiades and Aldebaran.
Within two hours after sunset, the Moon rises between E and ESE, some 15 degrees lower left of Spica. Within another half hour, Mars appears about 4 degrees to Moon's lower right. Moon creeps closer to Mars overnight, passing just 2 degrees above it in the SW sky before dawn on Saturday.
Nearly three hours after sunset, a line from Spica to Mars, 17 degrees long, extended 10 degrees beyond Mars to its lower left points to the waning gibbous Moon rising in ESE. Set your clocks forward one hour before retiring tonight, to observe daylight saving time.
An hour before sunrise on Monday, the Moon is in SSW, with Antares, heart of the Scorpion, 10 degrees to its lower left. Bright orange Mars is in SW, 24 degrees to the Moon's lower right.
An hour before sunrise on Tuesday, the Moon is just west of due south. The red supergiant star Antares is about 10 degrees to the Moon's lower right.
An hour after sunset, find brilliant Venus in the west, then look for Saturn 20 degrees below or lower right. The Pleiades or Seven Sisters star cluster is 7 degrees above Venus and becomes easy to see as the sky darkens. Aim binoculars at Venus, then raise them slowly, and the cluster will come into view at the top edge of the field about as Venus leaves the field's lower edge, if you're using 6x or 7x binoculars. Look nightly!
One-and-a-half hours before sunrise on Thursday, the Moon is in SSE. The 2nd-magnitude star Nunki, 6 degrees below the Moon, is in the handle of the Teapot, a part of Sagittarius, the Archer. Ten degrees lower right of Nunki, another 2nd-mag. star, Kaus Australis, the southern star of the bow, marks the bottom of the Teapot's spout. The six remaining stars of the Teapot are noticeably fainter, at 3rd magnitude. The Moon, approaching Last Quarter phase and just over half full, passes south shortly after sunrise.
Around sunrise on Friday, the Moon is in SSE. Just under half full and a few degrees less than a quarter-circle west of the Sun, the Moon is a few hours past Last Quarter phase.
As the evening sky darkens, look in the west for the beautiful Pleiades cluster 4 degrees upper right of Venus. Binoculars give an especially striking view.
An hour after sunset, the brightest objects, in order of brilliance, are Venus in the west; Sirius, the Dog Star, in SW; Arcturus in E; Capella, the Mother-goat Star, in WNW; Rigel, Orion's foot, in WSW; and Procyon, the Little Dog Star, 26 degrees above Sirius.
Tonight and Monday, Venus and the Pleiades cluster appear closest together, 3 degrees apart. As darkness falls, look W to WNW for the cluster just upper right of Venus. Light you see from the Pleiades tonight left those stars about four centuries ago. Sunlight you see from Venus was reflected from the planet's cloudtops less than 10 minutes before entering your eye. A little over two hours after sunset, Venus is 10 degrees up in WNW, while reddish Mars is 10 degrees up in ESE. Look for Spica 15 degrees upper right of Mars.
On Tuesday about 40 minutes before sunrise, the thin old crescent Moon is very low, about 15 degrees S of east. Use binoculars to search horizon for Mercury, about 10 degrees to Moon's lower left. Viewers in southern states can see Mercury with unaided eye.
Around this date each year, the orbiting Earth passes between Spica and the Sun, so the bodies Sun-Earth-Spica lie in a straight line. From the vantage point of Earth this time of year, Spica appears nearly 180 degrees from the Sun. Spica, rising on the opposite horizon from the setting Sun, is said to be at opposition. Look for Spica low in ESE at dusk, highest in S in middle of night (not at 12:00 a.m., but midway between sunset and sunrise), and low in WSW at dawn. This year, Mars is at opposition 11 days after Spica.
In the west an hour after sunset, brilliant Venus lies between Aldebaran, 10 degrees to its upper left and the Pleiades, 4 degrees lower right. Orion in WSW has two bright stars, Betelgeuse above the belt and Rigel below. Follow Orion's belt leftward to Sirius in SW, and rightward to Aldebaran in W. Watch for Mars just rising in ESE, 14 degrees lower left of Spica and 32 degrees lower right of Arcturus. Keep track of all these objects in coming weeks. If you look nightly one hour after sunset, you'll notice the stars in the west get lower each night, until they disappear during May. Venus, shifting its position against the stars, will remain visible until late July. Mars, creeping toward Spica, will linger very near that star from late May until mid-June.
The Moon is New tonight, at 12:22 a.m. EDT on Friday (or 9:22 p.m. PDT on Thursday). Mercury reaches its farthest apparent distance from the Sun for this year, 28 degrees on Friday morning. But it is hard to see from northern states. For example, from the latitude of East Lansing MI (42.7 degrees N), Mercury is only one degree above the horizon 40 minutes before sunrise. Using binoculars, scan the horizon about 5 degrees south of east. Observers in southern states will find Mercury higher and easier to see. In case you can't find Mercury, then enjoy bright Mars sinking toward the WSW.
First chance to see the young Moon: About 20 to 30 minutes after sunset this evening, use binoculars to scan horizon 10 degrees north of west. Moon is within 24 hours after New from eastern U.S. If you spot the hairline crescent, try for Saturn about 4 degrees right or lower right. Venus shines high above; Moon will pass 7 degrees to its south (lower left) on Sunday evening, and will cover the star Aldebaran from some locations. More Sunday.
Beautiful sights in the western sky for unaided eye and binoculars tonight and Sunday: Tonight an hour after sunset, the crescent Moon, with earthshine filling out its dark side, floats 15 degrees below Venus. The Pleiades glitter 7 degrees to Venus' lower right, and reddish Aldebaran, eye of Taurus, twinkles 8 degrees to Venus' left. Stars of the Hyades cluster complete a letter "V" with Aldebaran at the top of the left arm of the "V". Look again on Sunday!
The week of April 18-24, 1999 is National Sky Awareness Week. Our Diary entries for that week describe how to use the Moon to find Venus in the daytime, an occultation of the star Aldebaran, craters along the lunar terminator, the Lyrid meteor shower, and the greatest brilliancy and all-night visibility of Mars. For information on Sky Awareness Week, visit the website:
http://www.weatherworks.com/skyawareness.week.html
See Venus in the daytime! Just over 2-1/2 hours after midday -- the time halfway from sunrise to sunset -- Venus passes high in the south, 7 degrees above the Moon. With the approach of sunset, Venus is in the west, 7 degrees to Moon's upper right. From much of U.S. as the sky darkens, the Moon is framed within the "V" of Aldebaran and the Hyades, a beautiful sight of naked eye and binoculars until they set some 3 hours after the Sun.
Binoculars or telescopes give best views as Moon occults, or covers and uncovers Aldebaran this evening, as seen from N Central and NW U.S. and western Canada, N of a line from midpoint of Oregon's coast to northern Arkansas. Seen from S of that line, i.e. from CA and southern OR eastward to TX and most of OK and AR, the Moon's S edge (close to the left point of the crescent) narrowly misses the first-magnitude star.
The earthlit edge of the Moon, visible as a ghostly blue if it's late enough after sunset, suddenly snuffs out Aldebaran at the following approximate times: Seattle 8:10 p.m. PDT (just after sunset); Portland OR 8:18 p.m.; Great Falls MT 9:12 p.m. MDT; Boise ID 9:25 p.m.; Cheyenne WY 9:30 p.m.; Denver 9:38 p.m.; Minneapolis MN 10:15 p.m. CDT;, Pierre SD and Chicago 10:19 p.m.; St. Louis 10:28 p.m.; Kansas City 10:30 p.m.; Detroit, E. Lansing, and Grand Rapids MI 11:16 p.m. EDT. From west of a line through northwest WI, central IA, and eastern KS, both the star's disappearance behind the Moon's earthlit edge and its reappearance at the Moon's sunlit edge can be observed. Farther east, in Michigan, southwestern Ontario, NW Ohio, Indiana, southern Illinois, western Kentucky, southeast Missouri, northern Arkansas, and northwest Tennessee, Aldebaran is very low and about to set when the Moon covers it. In Michigan the star disappears behind the Moon's dark edge at times ranging from 11:10 p.m. EDT in the far northern part of the state to 11:20 p.m. near the southern end of Lake Michigan.
>From eastern U.S. and Canada, including New England and Middle
Atlantic states westward to southeastern OH, eastern KY, and nearly all of TN, the Moon sets before reaching the star, and no occultation can be seen. For more on tonight's occultation of Aldebaran, see p. 112 of April Sky & Telescope, or visit the website of the International Occultation Timing Association, at:
http://www.lunar-occultations.com/iota
In the west an hour after sunset, the waxing crescent Moon hovers about 16 degrees upper left of brilliant Venus and 13 degrees upper left of Aldebaran. Tonight and Tuesday Venus is 7 degrees N (upper right) of Aldebaran, the closest together we'll see them until July of 2001. Another reddish star, Betelgeuse, appears within 13 degrees to Moon's lower left.
To commemorate Astronomy Day, Saturday, May 22, our May Sky Calendar will be available to reprint for free distribution that month. To download a copy, check our website http://www.pa.msu.edu/abrams after mid-April, or if you would like a printed sample of the May Sky Calendar, send a long, self-addressed stamped envelope to: May Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824. For information about Astronomy Day, check Astronomical League's webpage on the subject at: http://www.astroleague.org/al/astroday/astroday.html
The Moon, one-third full, is halfway to overhead one hour after sunset. Betelgeuse, shoulder of Orion, is 15 degrees below the Moon, and the Gemini twins, Pollux and Castor, are some 18 degrees above. Second- mag. Alhena, heel of Pollux, lies 3 degrees to Moon's upper left. Procyon in Canis Minor is 21 degrees to Moon's left. Sirius, brightest nighttime star (but not as bright as Venus) twinkles in SW 26 degrees below Procyon.
At sunset the fat crescent Moon is high in SW, and Venus is in the west, a few degrees right of the point halfway from the Sun toward the Moon. Can you spot Venus before sunset? Binoculars and telescopes show two prominent lunar craters, Aristoteles and Eudoxus, along the Moon's terminator (day-night boundary), not far from the Moon's northern cusp (point of the crescent). The next few evenings are excellent for studying lunar surface features as the terminator shifts 12 degrees of lunar longitude daily. As sky darkens, look for Procyon 14 degrees to Moon's lower left, and the Gemini twins, Pollux and Castor, 9 and 13 degrees to Moon's upper right. The Moon will set around 4 hours before sunrise Thursday morning, and for the next 2-1/2 hours the sky will be dark and moonless, ideal for observing the peak of the Lyrid meteor shower. For more information on observing lunar surface features or about meteor showers, visit the Astronomical League website at http://www.astroleague.org Then click on Observing Clubs and choose Lunar Club or Meteor Club.
At midday today, as Sun passes high in south, the First Quarter Moon, half illuminated, is low about 15 degrees north of east. Sun and Moon are one-quarter circle or 90 degrees apart. By an hour after sunset, the Moon is high in SW and slightly over half full.
An hour after sunset the waxing gibbous Moon, nearly two-thirds full, is high in SSW. Bright reddish Mars is low in ESE, 11 degrees lower left of first-mag. Spica in Virgo. Regulus, heart of Leo, is about same distance left of the Moon. Tonight binoculars and telescopes give striking views of the smooth-floored crater Archimedes on the lunar sunrise terminator and the Apennine Mountains casting long shadows onto Mare Imbrium plain. Visible in telescopes is the Straight Wall, casting its shadow onto Mare Nubium.
Public viewing sessions at Michigan State University Observatory tonight and Saturday from 9 to 11 p.m. if skies are clear, will feature the Moon, Mars at its brightest, and other sky objects. Call (517) 355-4672 for a recorded message about The Cowboy Astronomer, presented 8 p.m. Fri. and Sat. and 4 p.m. Sundays at Abrams Planetarium.
An hour after sunset, four brightest objects are: Moon, high in S; Venus in W; Mars low in ESE; and Sirius, low in SW. Tonight the red planet Mars is at opposition and visible all night, as the Earth passes nearly between Sun and Mars. Now 54 million miles from Earth, Mars is closer and brighter than it's been since late in 1990, and will draw even a little closer until May 1st. Regulus, heart of Leo the Lion, is just 2 or 3 degrees to Moon's upper right at dusk. From most of eastern U.S., Moon covered that star during afternoon.
In SW to WNW within an hour after sunset, look for Sirius; Rigel and Betelgeuse in Orion; and Aldebaran and the Pleiades in Taurus. Record nightly sightings of these objects as they sink lower into the twilight glow each night; they'll all be gone within a few weeks.
An hour after sunset, look for the two planet-star pairs, each separated by 10 degrees, about the apparent width of your fist held at arm's length: In the west, Venus with Aldebaran to its lower left; and in the ESE to SE, Mars with Spica to its upper right. Mars is now appearing to retrograde, or to move backwards as the faster-moving Earth overtakes it, and will approach to within 2 degrees of Spica over the next 6 weeks. Keep watching!
Today Saturn is at conjunction on the far side of the Sun and is lost in the solar glare. By the end of May, it will emerge into the eastern morning sky to the lower left of Jupiter. An hour after sunset this evening, the Moon is in the SE. First-magnitude Spica and Mars, a dozen times brighter, are 15 and 23 degrees to Moon's lower left. Zero- magnitude Arcturus is in the east, 30 degrees to Moon's left.
>From dusk until first light on Thursday, Moon, Mars, and Spica form a
triangle as Mars follows Spica across the night sky by 9 degrees. On horizon just north of east 40 minutes before sunup on Thursday, departing Mercury is 4 degrees right of emerging Jupiter. Southern states are favored for seeing this difficult pairing in bright morning twilight.
Try to see Mars in the daytime! About 10 to 15 minutes before sunset, locate the nearly Full Moon low in ESE about 5 or 6 degrees above the horizon. Mars is 3 or 4 degrees to the right of the Moon and should be easy to see in binoculars. Can you spot it with unaided eye? An hour after sunset, Spica is visible within 9 degrees to Mars' upper right. Watch Moon slowly pull away from Mars until first light of dawn on Friday, when Mars and Spica appear in WSW, to Moon's lower right. The Moon sets shortly after sunrise on Friday, and is Full that day at 10:55 a.m. EDT.
Tonight's Grass or Egg Moon -- as the Full Moon at this time of year was called by Native and Colonial Americans -- rises no more than 15 minutes after sunset this evening, within contiguous 48 U.S. Look 16 degrees south of east and 14 degrees lower left of Mars.
On Saturday and Sunday mornings, use binoculars to find Jupiter and Mercury just 1.7 degrees apart, very low in bright twilight, a few degrees north of due east. Fainter Mercury is lower right of Jupiter on Saturday, below it on Sunday. From southern states, start looking 45 minutes before sunup; from northern states, you might not see them until 30 minutes before sunup, if at all. The Moon remains visible until it sets in WSW about an hour or so after sunrise on Saturday.