To the reader:
The Skywatcher's Diary for August 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
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If you would like a printed sample of the August issue, please send a long,
self-addressed stamped envelope to:
August Sky Calendar
Abrams Planetarium
Michigan State University
East Lansing, MI 48824
Each month, the Department of Physics and Astronomy at Michigan State
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Skywatcher's Diary: August 2001
Today is Lammas, the third cross-quarter day of the year, the date that traditionally signaled the halfway point between the summer solstice and autumnal equinox. Strictly speaking, August 7 is the date exactly between the solstice and equinox. The word literally means "loaf mass" or bread feast. It was a harvest festival formerly held in England. In some sense, today could be considered mid-summer, although with the schedules most people keep, summer is almost over.
Yesterday morning three pairs of objects were equally spaced--that is, the separation between each pair of components was 1 1/2 degrees. See if you can tell which pair is now different. Look in the east 1 1/2 hour before sunrise. The object pairs are Castor and Pollux (the Gemini twins), Jupiter and Venus, Saturn and Aldebaran (eye of Taurus). For a dramatic change, watch every morning for the next week.
Although now fainter than its brilliant display in June and July, Mars is still the brightest object in the evening skies, aside from the Moon. The planet is due south an hour after sunset. The bright star Antares, heart of Scorpius, is 7 degrees (less than a fist width held at arm's length) from Mars.
Tonight the Moon appears Full, although the exact moment occurs at 1:56 a.m. tomorrow morning. The Full Moon of August was traditionally known as the Green Corn or Grain Moon.
A celestial spectacular occurs over the next two mornings that most people will miss due to its early hour. The two brightest planets, Venus and Jupiter, pass just over a degree (2 moon widths) apart. The separation between the two planets is nearly identical each morning, but the orientation will be noticeably different. Venus, the speedier and brighter of the pair, slides under Jupiter, to the lower right. Look low in the ENE around the start of dawn. The duo is 15 degrees up 1 1/2 hours before sunrise. They will still be easy to see a half hour later when they climb to 20 degrees up.
Continue following the Venus-Jupiter encounter every clear morning at day's first light. Saturn, too, is in the vicinity--just over 20 degrees to the upper right of the bright planet pair. The Ringed Planet resides among the stars of Taurus. Aldebaran, the brightest star of that constellation, is 5 degrees to Saturn's right. The mighty hunter Orion is in the same region. If you don't immediately notice it, look below Saturn and to the right of Venus and Jupiter.
If you have transparent skies and a flat horizon to the south, see how much of Scorpius, the Scorpion's, tail you can trace. Look below Mars, in the south near the end of dusk. The stars form a curve that bends around on itself toward the left, like the end of a fishhook. The barb of the hook is marked by two stars close together. Shaula, the brighter of the pair, is almost 1st magnitude. Its companion is a magnitude fainter. The name "Shaula" is Arabic in origin. It means "the sting," referring to the star's position in the scorpion's anatomy.
Tomorrow morning look for Venus 1 1/2 degrees almost directly below Jupiter.
Sagittarius is a favorite summertime constellation. It sits directly to the left (east) of Scorpius. Once you discover the "teapot" shape that most people use to recognize this pattern, it will likely become a favorite. The constellation is not bright--it has no stars more luminous than 2nd magnitude--but the pattern easily catches the eye once you know what to look for. The brightest star, Kaus Australis, is ten degrees (a fist width) to the left of the tip of Scorpius' tail. It lies at the bottom of the "spout." Another 10 degrees to the left is the "handle." If you have trouble locating anything identifiable, use a star map to familiarize yourself with the pattern.
In addition to offering a pleasing shape to search for, Sagittarius hosts some of the best "deep sky" observing. A few degrees to the upper right of the spout lies the direction to the center of the Milky Way galaxy. The hazy rim of our galaxy then bends back toward the upper left, as though it were steam rising from the spout. The Lagoon Nebula, a stellar nursery and warm weather equivalent of the Orion Nebula, is in the vicinity, as are the pretty open star cluster M7 and the globular star cluster M21, to name only a few treats. Several of these objects are visible with unaided eye; many more are accessible through binoculars. Scanning the region on a crystal clear and moonless night provides numerous interesting sights even if you don't bother to consult a star chart to identify the objects.
The Summer Triangle now sits high up in the east at the end of evening twilight. The three widely-spaced stars that mark the corners of the triangle are the brightest objects on that side of the sky. Vega, the most luminous, is nearly overhead. Follow a little more than three fist widths to the southeast to find Altair, the second brightest. Lastly, Deneb is two fist widths ENE of Vega and almost four from Altair. The Summer Triangle is an asterism, an obvious pattern that isn't an official constellation. The Big Dipper is the most famous asterism. It belongs to the constellation Ursa Major, the Great Bear. The Summer Triangle borrows its stars from three constellations: Lyra, the Harp (Vega); Aquila, the Eagle (Altair); and Cygnus, the Swan (Deneb).
As the solar system orbits the center of our Milky Way galaxy, we are thrust toward Deneb, the faintest of the trio of stars than comprise the Summer Triangle. Deneb is intrinsically one of the brightest stars in our galaxy, but its great distance dims the star's brilliance to that of a respectable, but not spectacular, 1st magnitude. Deneb lies 1500 light years from Earth, or 9 thousand trillion miles. The light reaching us tonight began its journey from Deneb as the Barbarians were sacking Rome. If we lived long enough to witness the Earth's arrival at Deneb's location, we would miss a close encounter with the star. Deneb long since moved on.
The "summer cottage meteors," officially known as the Perseids, reach their peak during the predawn hours tomorrow. The Last Quarter Moon joins the party just before midnight to obscure the fainter meteors. Consequently you may want to take a look before moonrise. Since the peak of the Perseid shower is broad, you will see a number of meteors a day or two before and after the maximum. Meteor watching is best done on your back, allowing your eyes to take in as much of the sky as possible, since the "shooting stars" can appear anywhere in the sky.
The Moon reaches Last Quarter at 3:53 a.m. EDT. The label "quarter" can seem confusing since the Moon is half illuminated. The term refers to the fact that the Moon has gone three-quarters of the way around its orbit since the last New Moon--a useful concept if you use the Moon as a calendar. Trivia question: How much fainter than the Full Moon is the Last Quarter Moon? Fifty percent would seem the simple answer, but the Last Quarter gives off only 8% the light of Full Moon.
At the first light of dawn, the waning crescent Moon is 10 degrees (a fist width) to the upper right of Saturn. The bright star Aldebaran, eye of Taurus, is 6 degrees to the lower left of the Moon and 5 degrees to the right of Saturn. Between the planet and the Moon and above Aldebaran lie members of the Hyades star cluster, a loose collection of stars held together by the stars' mutual gravitational attraction. Aldebaran, although not a member of the cluster, is often "attached" to the group to complete a "V" shape pattern to symbolize the face of Taurus, the Bull.
Over two mornings the crescent Moon navigates the space between Saturn and Jupiter. This morning it is 4 degrees (half a fist width) to the lower left of Saturn and tomorrow morning perches 6 degrees to the upper right of Jupiter. Both times the Moon and 3 planets (Venus, Jupiter and Saturn) form a diagonal line 3 fists long in the eastern sky.
For most of North America the Moon passes in front of Jupiter this afternoon, covering it for a period of time. The event occurs after 4:30 p.m. EDT for most of lower Michigan. Find the crescent Moon about 15 degrees up in the WNW. Point a telescope at it and the planet should be in the same field of view.
By tomorrow morning, the Moon edges closer to Venus, passing within 2 degrees (4 moon diameters) of the brilliant planet, producing a picture-perfect scene.
Tomorrow morning is the last easy chance to see the Moon before New. One and a half hours before sunrise the thin waning crescent is just above the ENE horizon. The three planets extend to the upper right of the Moon almost 50 degrees (5 fists) across the eastern sky. These four objects nicely trace the plane of the solar system. The two Gemini Twins, Pollux and Castor, sit 10 degrees above the Moon.
Uranus just passed opposition, so now is an excellent time to look for the planet. It is closest to Earth and brightest, although normally still requires optical aid to glimpse. The planet is above the horizon all night but is best viewed in the middle of the night when it is due south and highest--about 30 degrees up. The 6th-magnitude bluish dot gets a couple tenths of magnitude brighter at opposition, which challenges observers to try to detect it with unaided eye. To do so you will need a dark, transparent sky and a finder chart that accurately shows the planet's position among the stars of Capricornus.
The Moon is new at 10:55 p.m. EDT. Luna also reaches perigee (closest point to Earth in its orbit this time around) 3 hours later. The coincidence of New Moon and perigee creates larger than average high tides for those along sea coasts. Six months ago the same concern was raised about large tides, but then it was the concurrence of the Full Moon and perigee.
For those who enjoy the challenge of sighting a young moon less than 24 hours old, you have an opportunity tonight. Begin looking 20 minutes after sunset 10 degrees to the north of west. The Moon will be only 4 degrees above the horizon. Use binoculars. Bonus points are awarded for capturing Mercury, 3 degrees (6 moon diameters) to the lower left of the Moon.
The first easy young Moon appears tonight. If you don't find it right away, look low in the west about 45 minutes after sunset. Just after moonset take a telescopic peak at Mars. It is highest then, in the south, but still only 20 degrees up (two fist widths). The most prominent dark marking, Syrtis Major, will be centered on the disk. Watch through the telescope for those fleeting moments when the air settles down and you get particularly sharp views--that is, if the planet-wide Martian dust storm has finally subsided.
If you have the opportunity to be at a dark-sky site during the next 10 days or so, look for the zodiacal light before the start of dawn. This time of year the plane of the solar system makes a steep angle with the morning eastern horizon, as delineated now by Venus, Jupiter and Saturn. This geometry allows us to more easily see sunlight faintly reflecting from the minute flecks of dust swimming among the planets--the effect we call zodiacal light. This delicate illumination takes the form of a triangle or pyramid about 60 degrees wide by 60 degrees high with vertical axis aligned with the solar system plane. Be sure to look before the beginning of morning twilight so as not to confuse the two effects.
The four-day-old crescent Moon hangs above Spica, the brightest star in Virgo, in the WSW an hour after sunset. Brighter Arcturus is nearly 30 degrees (3 fists) to the Moon's upper right. The old saw for finding these two stars using the Big Dipper's handle--"Follow the arc to Arcturus and speed on to Spica"--must be amended tonight to include "mosey to the Moon."
The stars Arcturus and Spica provide an interesting comparative study. Arcturus, currently the brightest star in the evening sky, gives off an orange hue that indicates it is relatively cool--cooler than our yellow sun, for instance. Spica produces a much more blue-white light, revealing its tremendous temperature. If the two stars were placed side-by-side in space, Spica would be 16 times brighter than Arcturus. We must conclude, therefore, that in actuality Spica is considerably farther from us than Arcturus. The former is 260 light years distant, the latter, 37 light years.
One of these mornings before sunrise, notice how far apart Venus and Jupiter have drifted since earlier in the month. On August 5th, less than 2 degrees separated the two planets, and now they are 18 degrees apart. By month's end Jupiter will sit halfway between Venus and Saturn, 25 degrees from either planet.
The First Quarter Moon is entering the realm of Scorpius and Sagittarius. Tonight it is 8 degrees (almost a fist width) to the upper right of Antares, the heart of the scorpion. Tomorrow night it slides between the star and Mars, but higher than either.
Tomorrow morning Venus lines up with the Gemini Twins, Pollux and Castor. The planet is 9 degrees from Pollux and 14 degrees from Castor. Check the alignment again the next chance you get.
During the next 24-hour period, the Moon leapfrogs over Mars. It perches 7 degrees to the upper right of the planet tonight and the same distance to the upper left tomorrow evening. It moves from the constellation Ophiuchus to Sagittarius. If you are not familiar with Ophiuchus (pronounced ah-fee-you'-kus), the Serpent Charmer, you should learn to identify it. By astronomers' definition, it is one of the zodiac constellations.
Take the opportunity, if you can, to observe Saturn with a telescope some morning in late August or early September. The planet's rings are tipped the greatest from edge-on for this year--26.2 degrees. Look for Saturn's shadow cast upon its rings, as well as the major gap in the rings called "Cassini's division," and the planet's brightest moon, Titan.
The waxing gibbous Moon sits 2 degrees (4 moon diameters) atop Nunki, a 2nd-magnitude star in the handle of the "teapot" of Sagittarius. The "lid" is to Luna's right, half a fist away, and the "spout" farther to the lower right. Nunki was known in Babylonian times as the "Star of the Proclamation of the Sea." This title acknowledges that the star leads the "watery" constellations across the sky. Note Capricornus, Aquarius, Pisces, Pisces Austrinus, and Delphinus all lie immediately to its east.
Mars began this month 7 degrees to the left of the star Antares. Tonight the two objects span 16 degrees. Mars appears to be picking up speed since it came to a momentary standstill on July 19, 5 degrees left of Antares. The planet's acceleration is illusionary. Its orbital speed is not significantly different, but our perspective from Earth has changed considerably, as we pull away from the Red Planet. A month from now the angular separation between Mars and Antares will be twice as great--32 degrees.
Pegasus now gallops into the eastern sky as night settles in. It brings with it the beginnings of seasonal change as the evening sky transforms from the stars of summer into the autumn patterns, paralleling changes on Earth. Look for the Great Square of Pegasus, 4 nearly equally bright stars separated by about 15 degrees (a fist and a half) on a side. The square is rotated into a diamond pattern with one corner pointing down to the horizon just to the north of due east. The great Andromeda Galaxy lies to the left of the square. Binoculars will be needed to spot the galaxy unless the sky is very dark.
Delphinus, the Dolphin, proves that a constellation does not need to be bright to be readily identifiable. The pattern is small--only 5 degrees across--and faint--no star brighter than 4th magnitude. First find Altair, the southern most member of the Summer Triangle. Search about 15 degrees to the left and slightly above that bright star for a small parallelogram, 2 degrees on a side. Bright moonlight may hide the shape, particularly if the sky is hazy. Once you see the pattern, however, you will remember it and be able to find it with ease in a dark sky.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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