To the reader:
The Skywatcher's Diary for July 2002 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 July issue, please send a long,
self-addressed stamped envelope to:
July 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
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Skywatcher's Diary: July 2002
Venus rules the evening sky. It sets slightly more than 2 hours after sunset tonight, and a little less than 2 hours after sundown by month's end. Jupiter and Mars are, technically, evening objects, setting 45 minutes after sunset, but because of their proximity to the sun, they will be difficult to spot. Jupiter will require binoculars and Mars may need something more powerful.
If you are looking for an event to celebrate, an excuse to start Independence Day festivities early, the midpoint of the year occurs tomorrow at midday (1 p.m. EDT).
The closest two-planet pairing of the year takes place before dawn this morning. Mercury is 0.3 degrees (half a moon diameter) to the right and slightly lower than fainter Saturn. Look in the east-northeast 45 minutes before sunrise. The duo is less than half a fist width above the horizon at that time. Use binoculars. Over the next week you can watch Saturn continue to climb out of the twilight glow while Mercury plunges down into it.
The Moon reaches Last Quarter this afternoon at 1:19 p.m. EDT.
Pluto, the tiny ice planet, reaches its highest point around midnight. To spot the distant orb you will need at least an 8-inch
telescope and ideal observing conditions. It resides in the lower portion of the constellation Ophiuchus (off-ee-YOO-kuss), the
Serpent Charmer, and about 15 degrees to the upper left of Antares, the heart of Scorpius. Use a detailed chart of Ophiuchus that
clearly marks Pluto's current position. Try, for example, http://skyandtelescope.com/observing/objects/planets/article_612_1.asp
Tonight after the fireworks fade, take a moment to survey the "star-spangled banner" displayed overhead - the summer night sky. The brilliant, 1st-magnitude stars now up include the Summer Triangle, three widely separated stars on the eastern side of the sky. Then glance toward the south to spot ruddy Antares, about 2 fists (20 degrees) above the horizon. Swing southwest and catch Spica, one-third of the way toward overhead, and brighter Arcturus above it, two-thirds of the way up. Finally, spot dazzling Venus, low in the west, with 1st-magnitude Regulus 7 degrees (less than a fist) to the planet's left and slightly higher.
Summer is a good time to become acquainted with some of the fainter constellations, particularly if you visit a remote setting where ambient lighting is minimal. Corona Borealis, the Northern Crown, is a good one to begin with since its distinctive shape is relatively easy to spot. First, locate Arcturus and Vega. The constellation lies on a line between these bright stars, but closer to Arcturus, 20 degrees (2 fists) to the upper left of that star. The constellation's brightest member is 2nd-magnitude Alphecca, or Gemma. The latter designation refers to its placement as the "jewel in the crown." Fainter stars flank Alphecca on both sides and curve upward, producing a dim semicircle that, with some imagination, might be pictured as a tiara. A full-fledged crown will take more of a mental stretch.
Today the Earth is farthest from the sun for the year. Astronomers refer to this event as "aphelion," derived from Greek meaning "from the sun." Just after midnight the sun and Earth were 94,506,950 miles apart. This figure varies by about 3 percent from the closest approach of these two bodies (perihelion) that occurs in early January. Take note that today is not the coldest day of 2002, so the annual temperature swings we endure must have a cause other than how far away the sun is.
This morning before sunrise the crescent Moon sits 4 degrees (half a fist) to the upper left of Aldebaran, in Taurus. Saturn is about 10 degrees (a fist) to the lower left of the Moon, and Mercury sits 8 degrees to Saturn's lower left. Tomorrow morning the Moon perches only 3 moon diameters (1 1/2 degrees) above the Ringed Planet, and the following morning Luna slips 1 degree to the left of Mercury. To follow these events, look each morning near the east-northeast horizon 30 to 45 minutes before sunrise. Mercury comes up only an hour before the sun.
Hercules makes a good target to sharpen your faint constellation finding skills. It lies on the line between bright stars Vega and Arcturus, about one-third of the way from Vega and next to Corona Borealis. The defining pattern to search for is a wastebasket shape, sometimes called the "keystone." It consists of 4 stars, two 3rd and two 4th-magnitude, so you will need to observe from a relatively dark location. The wastebasket has three sides each 7 degrees in length. The remaining side spans 4 degrees. The fabled globular star cluster, M13, resides on the west (right) side near the top. Use binoculars to search for a fuzzy spot.
Carefully examine the region around Venus over the next several nights (low in the west after sunset). Tonight the brilliant planet is 1.3 degrees (about a finger width) to the right of Regulus, the heart of Leo, the Lion. Although Regulus is the brightest star in that constellation, and 1st magnitude, a casual observer could easily miss seeing it. Tomorrow night the planet moves slightly closer and above the star. Every night thereafter, Venus pulls farther away from Regulus, as the star descends and disappears into twilight by the end of the month.
The Moon passes New phase this morning at 6:26 a.m. EDT. Look for the fragile crescent to first appear tomorrow evening near the west-northwest horizon 30 to 45 minutes after sunset.
Second-magnitude Denebola, the tail of Leo, the Lion, hangs a third of the way up in the west an hour after sunset. Venus sits 23 degrees (2 fists) to the star's lower right, tonight, and draws nearer as the days go by. The planet passes 13 degrees beneath the star on July 24.
Canes Venatici (KAIN-ees veh-NAT-ih-see), the Hunting Dogs, is a faint constellation found between the Great Bear's tail (end of Big Dipper) and Leo's tail (Denebola). Its brightest member is Cor Caroli, a 3rd-magnitude star located 14 degrees (fist and a half) to the lower left of the last star in the Big Dipper's handle, and 26 degrees to the right of Arcturus. Edmund Halley, of comet fame, coined the star's name to honor Charles II of England. The dogs are pictured barking at the heals of the Great Bear while Bootes, the Herdsman, tugs at their leashes, in an attempt to restrain the beasts.
The attractive crescent Moon sits 6 degrees (12 moon diameters) to the right of Regulus, the Lion's heart. Venus hangs just 3 degrees to the star's upper left. Tomorrow night the Moon climbs 7 degrees to the upper left of the planet. Both nights offer an alluring sight. As the twilight darkens, be sure to note the earthshine, the shadowy "dark" side of the Moon. It is a beautiful view with unaided eye and binoculars.
Canes Venatici (see July 11th) lies between the Bear and the Lion. Begin drawing a line from the end of the Big Dipper's handle to the tail of Leo (Denebola). One-third of the way you pass through Canes Venatici. Two-thirds of the way you are among the very faint stars of Coma Berenices (KO-ma bear-eh-NICE-ees), the Hair of Berenice, Queen of Ethiopia. The brightest stars are only 4th-magnitude, so you need the darkest sky possible. Instead of looking for a particular pattern, try to find a scattering of faint stars in the vicinity. Someone described the constellation appearing as though salt had been sprinkled there. The stars, which to some give the appearance of long tresses, belong to a cluster of stars, usually known simply as the Coma Cluster.
The Moon perches 8 degrees (a fist) to the lower left of Denebola, the lion's tail. The crescent is becoming large enough that surface features begin to emerge, particularly in binoculars and telescope. The large dark oval that appears above middle and right is Mare Crisium (MARR-ay CRY-see-um), the Sea of Crisis. The feature is not a sea, but rather a crater that has been flooded with lava at some remote time in the Moon's history. It measures 270 miles north-south by 350 miles east-west, which means it should appear wider than higher. We see a nearly circular aspect, however, because the crater sits around the edge of the Moon, from our viewpoint, causing the feature to appear foreshortened.
The waxing crescent Moon now resides among the stars of Virgo. That fact will become more obvious tomorrow night when the Moon passes 5 degrees (half a fist) above Spica, the brightest star in that constellation. Tonight Luna sits 2 degrees (4 moon diameters) to the right of Porrima (also Gamma), a 3rd-magnitude member of Virgo. Porrima is actually a well-known binary - two 4th-magnitude stars in a 171-year orbit around each other. The orbit is quite elliptical, and at times the stars are drawn so close together that they are difficult to distinguish in telescopes. The next such "close encounter" occurs in 2007.
The Moon reaches First Quarter phase tonight at 47 minutes past midnight (EDT). That's technically tomorrow morning, so most commercial calendars will mark the phase on the 17th. The Moon sets a short time later - 20 to 30 minutes after turning First Quarter. You would expect that if you had lived back when society was more agrarian. Farm families knew that the First Quarter Moon followed the sun across the sky by about a quarter day, and similarly, that the Last Quarter Moon preceded Sol by the same amount.
Tonight the gibbous Moon leaves Virgo and crosses the boundary into Libra (LYE-bra), the Scales. This faint group is the only zodiac constellation that represents an inanimate object. The two brightest stars are only 3rd magnitude. One of them, Zubenelgenubi (zoo-ben-ell-jeh-NOO-bee, or Alpha), lies 8 degrees (almost a fist) to Luna's left, and slightly lower. The star's name is derived from ancient Arabic, meaning "southern claw." It refers to the fact that the star at one time was considered one of the scorpion's appendages.
The Moon remains in Libra, tonight. Zubenelgenubi now lies 6 degrees to Luna's right. Its companion, Zubeneschamali (zoo-been-ess-shah-MAH-lee, "northern claw") sits 7 degrees above the Moon. The two star names are among those most widely recognized by amateur astronomers. Experienced stargazers enjoy impressing neophytes by tossing the star names into conversation. With a little practice, the names easily roll off the tongue. Try it yourself at the water cooler tomorrow. Mention to a colleague, "I noticed Zubenelgenubi was near the Moon last night," and watch the reaction you get.
Tonight the Moon can be found in the south at nightfall, 7 degrees to the upper right of Antares, the brightest star in Scorpius. Tomorrow night look for Luna 9 degrees to the left of the star. Although Antares is 1st magnitude, for a variety of reasons it often appears fainter. From mid northern latitudes the star rises no higher than about 20 degrees off the horizon. The atmosphere appears thicker at that altitude and even when the air is transparent, an object's brightness is reduced by half a magnitude. In the summer, when Antares is most often observed, the atmosphere frequently is not transparent, but hazy, further dimming the star's brilliance. Finally, Antares' reddish color makes the star seem fainter to the eye than astronomical instruments would measure.
You haven't heard much about Jupiter since it dropped out of sight late last month. The giant planet has been trudging along its orbit, as has the Earth. As a result of these two motions, Jupiter now sits behind the sun, at what astronomers call "conjunction," or more properly, "conjunction with the sun." Because Jupiter's orbit is on a slightly different plane than ours, the planet usually appears above or below rather than directly behind the sun. This time it passes above. Conjunction also marks Jupiter's official anointment as a morning object. Several more weeks must pass, however, before Jupiter becomes visible in the dawn glow ahead of sunrise.
Yesterday Jupiter reached conjunction; today it is Mercury's turn. The situation is somewhat different, however, with this fastest of planets. Because Mercury's orbit is smaller and inside the Earth's orbit, when it lines up with Sol, the planet can appear in front of or behind the sun. To distinguish those two possibilities, astronomers refer to superior conjunction when Mercury is beyond the sun and inferior conjunction when it lies between Sol and us. Today we note the former. With superior conjunction Mercury technically passes into the evening sky, but it won't become visible until the second week of August, and then with difficulty.
Saturn is now plainly visible in morning twilight. An hour before sunup this 0th-magnitude object hovers 16 degrees (1 1/2 fists) above the east-northeast horizon. Fifteen degrees to its upper right sits slightly fainter Aldebaran, eye of Taurus. Seeing the Bull alerts us that the wintertime evening constellations are beginning to emerge now in morning twilight. Betelgeuse, the right shoulder of Orion, lurks 16 degrees to lower right of Saturn, just above the eastern horizon. Although currently difficult to pick out against the bright sky, Betelgeuse will be obvious in a couple weeks.
For a star map to help locate Saturn and these stars, send a self-addressed, stamped envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824.
Tonight the Moon rises within a few minutes of sunset. This fact should tell you what phase to expect. Full Moon, right? That phase doesn't officially occur until 5:07 a.m. EDT tomorrow morning, but the rule of thumb works fine within a day of the exact moment. And what time would you supposed the Moon sets tomorrow morning? The answer is sunrise. The Full Moon stays up all night long. This month's Full Moon was known in colonial times as the thunder moon, hay moon, or simply, summer moon.
An hour after sunset Venus is due west and 10 degrees (a fist) off the horizon. The planet is plainly visible as long as your western view is not obstructed. Denebola, the 2nd-magnitude star marking the tail of Leo, stands 13 degrees above the planet. So it is a little more than twice the height of Venus. The brightest star in the lion, Regulus, is also still visible but much harder because it sits so low, only 3 degrees above the horizon, and 16 degrees to the lower right of Venus. Fifteen minutes earlier will improve your chances to capture this star. Use binoculars.
How much longer will you be able to find Regulus, the heart of Leo? The star will be beyond the sun and clearly not visible in a month. Between now and then a point is reached when twilight does not fade quickly enough to allow you to see Regulus before the star sets. This phenomenon is called the "heliacal setting" of Regulus. The event happens at the same time each year and was recognized by our ancestors as a means of keeping track of time on a yearly scale. Different stars have different heliacal settings, thus providing a way to more finely divide the year. A similar heliacal rising of stars occurs before sunrise.
Tonight the Moon rises at the end of twilight, so we enter the time of month when evenings become free of moonlight and dark skies prevail. Now we can more successfully hunt those dim objects and constellations. Here's a faint summertime constellation that is easy to remember after you initially locate it. Delphinus (dell-FINE-uss), the Dolphin, lies in the vicinity of Altair, the lower or more southerly star of the Summer Triangle. At the end of twilight, about 1 1/2 hours after sunset, Altair rests halfway up in the southeast. Delphinus sits 12 to 15 degrees to the left of Altair. Search for four 4th and 5th-magnitude stars that form a tight parallelogram with equal sides (rhombus). That figure represents the mammal's body. The tail is marked by another 4th-magnitude star 4 degrees to the lower right.
Another small, faint constellation worth seeking out in the vicinity of Altair and Delphinus is Sagitta (sah-JIT-ah), the Arrow. It contains four 4th-magnitude stars about 10 degrees above and slightly to the left of Altair. The figure lies horizontal with one star marking the left point (arrowhead), one in the middle and two on the right, one above the other, reminiscent of a feather tail. The entire pattern is 5 degrees in length. The arrow appears to be in flight toward the left. In some accounts it's Cupid's Arrow gone astray.
Most farmers' almanacs note that the Delta Aquarid meteor shower reaches maximum tonight and tomorrow morning. Calling it a shower is probably misleading. On the average not more than one meteor appears every 3 or 4 minutes. In addition, the shower is broad, so no sharp peak exists. The flow is steady over a two-week period. The Delta Aquarids should be thought of more as a slight increase in the background rate of meteors. They are also a reminder to get ready for the Perseids in mid August - the real summer meteor shower.
The direction toward the center of our Milky Way galaxy now reaches its highest point in the south near the end of evening twilight. Although the center of our galaxy is a frenzied place with enormous amounts of energy flying about, no clear indicator pinpoints its location for the unaided human eye. From our vantage point it looks pretty much like any other spot along the Milky Way. Nevertheless, that unmarked place is worth seeking out because of what lies beyond our vision. First, identify the constellation of Sagittarius, often imagined as a teapot shape. It sits to the left (east) of Scorpius. The right side of Sagittarius represents the "spout." A line drawn from the bottom of the spout to the lip and extended that same length brings you approximately in line with the galaxy's center.
The Andromeda Galaxy is creeping back into the evening sky. This massive object, larger than our Milky Way, is the only galaxy aside from our own that can be observed with unaided eye from northern latitudes. At the end of twilight the Andromeda Galaxy sits 16 degrees (1 1/2 fists) up in the northeast. Sweep the area with binoculars, looking for a hazy, faint oval. Note its position but don't be in a hurry to scrutinize this dim object. Let it climb in the sky for as long as you can wait. Then carefully examine it with unaided eye and binoculars.
An hour before sunrise, look for Saturn a quarter of the way up in the east. Can you detect the 3rd-magnitude star 1 degree (less than a finger width) to the lower right of the planet? This star is Zeta in Taurus, a tip of one of the Bull's horns. Saturn will make 3 trips by this star between now and April of 2003. Astronomers refer to such an event as a triple conjunction. The planet first slides by the star moving east. Then Saturn retrogrades westward past Zeta at the end of the year, before completing the "triple play" in April.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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