To the reader:
The Skywatcher's Diary for June 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 June issue, please send a long,
self-addressed stamped envelope to:
June 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: June 2001
As dusk settles in, the star Spica, in Virgo, appears 6 1/2 degrees (13 moon diameters) below the waxing gibbous Moon. The brighter star Arcturus is 26 degrees (more than two fist widths) to the Moon's upper left. Tomorrow evening the Moon will slide 14 degrees to Spica's left.
Two bright planets greet early risers. An hour before sunrise Venus gleams low in the east -- the brightest object in the sky. Much farther to the right, in the SSW, Mars sits low, giving off a distinctly orange cast. Mid-month the war-god planet reaches its brightest in 13 years.
Mars now rises in the SE an hour after sunset. The planet traces an arc across the southern portion of the sky as the night progresses, reaching its highest -- about 20 degrees up in the south -- around 2:30 a.m. Mars eventually sets near SW a little less than an hour after sunrise, but a keen observer will lose it before then -- around 45 minutes before sunrise.
Pluto is opposite the sun today, so it is visible all night and highest in the middle of the night. The farthest solar system planet is, therefore, best seen now. The term "best" is certainly relative. Pluto is never easy. The small icy body is so distant that reflected sunlight from Pluto takes 4 hours to reach us. In order to have any hope of detecting this light you'll need at least an 8 or 10-inch telescope and a good finder chart.
The Moon is Full at 9:39 p.m. EDT, just after it rises in the SE. By the end of twilight Mars can be found 10 degrees to the Moon's lower left. The Moon passes within 4 degrees of the Red Planet during daylight hours tomorrow, when the pair is out of sight. Tomorrow night the twosome will rise together, side by side, 45 minutes after sunset.
As evening twilight fades, the Gemini Twins, stars Pollux and Castor, sit 15 degrees (a fist and a half) above the WNW horizon. Pollux, the slightly more luminous brother, is on the left. Capella, even brighter than Pollux, is slightly lower and farther to the right, nearer NNW. Watch these stars drop lower into brighter twilight as the month progresses.
Three bright objects rise in the SE, one after the other, an hour apart. Beginning at sunset, Antares, the brightest star in Scorpius, crosses the horizon. Then comes Mars and, later, the waning gibbous Moon. By the time the Moon is up, 2 hours after sunset, the three bodies form a diagonal line stretching about 30 degrees (3 fists) from lower left to upper right.
Venus rounds the bend in its orbit today, as seen from Earth. The astronomical term for this celestial geometry is "greatest elongation." If you followed Venus until sunrise, extended one arm toward the sun and the other toward the planet, the angle between your arms would equal 46 degrees. In a telescope Venus appears half illuminated.
Syrtis Major, the most prominent dark feature on Mars, is centered on the planet's disk tomorrow morning at 1:41 a.m. Mars is also near its highest point in the southern sky at that time, making telescopic viewing optimal. These two events won't coincide again for 5 weeks, albeit at a friendlier time of night -- nearly three hours earlier.
This week five solar system bodies are nearly lined up in space. In sequence, as seen from above the solar system, are Mars, Earth, Mercury, Sun, Jupiter. Lest you worry about a greater likelihood of earthquakes or other natural disasters, no scientific evidence has ever been found to suggest planetary alignments are anything other than a curiosity.
Since early May, Mars has traveled westward against the more distant stars of Sagittarius and Scorpius. This apparent motion is counter to the direction the planet moves in its orbit. It results when the speedier Earth passes Mars. Relative to us the planet moves "backwards." In two days Mars will be in the middle of its retrograde loop, which continues until mid-July.
If you haven't yet seen the complete Summer Triangle, look eastward at dusk. Altair is 10 degrees up. Vega is brightest and highest, 40 degrees up in the ENE. The third star, Deneb, is NE, 25 degrees high. The pattern takes its stars from three different constellations. Astronomers call such quasi-constellations "asterisms." The best known asterism is the Big Dipper.
The long awaited Mars opposition occurs today. Mars sits opposite the sun in the sky, as seen from Earth. It rises at sunset, sets at sunrise, and crosses due south in the middle of the night. This arrangement happens every 26 months, on average, but not all Mars oppositions are equally interesting. Conditions similar to the present opposition haven't occurred since 1988.
An opposition is created when our planet overtakes one of the slower moving planets -- those beyond Earth's orbit: Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Mars oppositions get more attention than the others because we swing much closer to the Red Planet, providing a dramatic change in our view of Mars, both with unaided eye and telescope. Over the last 9 months Mars has gone from an indistinct magnitude +1.8 object to the current near record-setting -2.4 dazzler. That's a 50-fold increase in brightness.
While Mars is a celestial eye-popper right now, Jupiter, almost as bright, gets no mention whatsoever. Why should that be? Does Mars have a better press agent? Although Jupiter is bright, it is nearly in the same line of sight as a much brighter object -- the sun-- and, so, is unobservable. Early next month we can catch the giant planet emerging in dawn's glow.
Similar to Jupiter's current fate, Mercury is also nearly aligned with the sun and not visible from Earth. Jupiter is, however, on the far side of the sun, while Mercury is almost between us and our day star, a configuration known as "inferior conjunction." Occasionally the swift-moving planet passes directly between Earth and sun and we witness a transit of Mercury across the sun's disk. The next Mercury transit occurs in 2003.
Today marks the autumnal equinox for Mars' northern hemisphere. The sun is shining directly on the planet's equator, and the southern hemisphere -- the south pole in particular -- is breaking out of winter. For telescopic observers the south polar ice cap should be near maximum.
This morning the beautiful waning crescent Moon hangs in the east 6 degrees (12 moon diameters) to the lower left of Venus. Tomorrow morning the Moon is almost two fist widths (18 degrees) to the planet's lower left, but only 7 degrees to the upper right of faint Saturn, just emerging from its stint of obscurity behind the sun.
The brightest star you can find a fist or so up in the west near the end of evening twilight is Regulus, heart of Leo, the Lion. Although officially 1st magnitude, it is the faintest of that classification. The light from Regulus reaching Earth tonight left the star 77 years ago. If Regulus were to take the place of our sun, it would appear several times larger, more blue-white in color, and 140 times brighter. What a different place the Earth would be.
Tomorrow Mars is 42 million miles from Earth, closer than it has been since 1988. At first thought, it might seem that Earth and Mars should have been closest at opposition, back on June 13th. On that date, however, Mars' orbit was still curving toward Earth's, so that the distance between the planets continued to decrease until today. The next minimum between these two planets occurs in August of 2003, an even closer 35 million miles.
Summer officially begins (for northern hemisphere) at 3:38 a.m. EDT. While it is true that today is the longest day (and shortest night), the earliest sunrise occurred on June 14th (for latitude 40 degrees N), and the latest sunset happens on June 27th. The Earth's non-circular orbit and tilted rotation axis account for this apparent discrepancy, though not in a straightforward manner.
Look for the very thin crescent Moon tonight low in the WNW between 45 minutes and an hour after sunset. The Gemini Twins, Pollux and Castor, are about 6 degrees (12 moon diameters) to Luna's upper right. Binoculars will be helpful in locating the Moon during brighter twilight.
The young Moon is outstanding tonight. It hovers alone in the WNW through twilight. The closest bright stars are the Gemini Twins, 17 degrees (about two fists) to the lower right, and Regulus, of Leo, 22 degrees to the upper left. No matter. It deserves your undivided attention.
An hour after sunset the crescent Moon is 7 degrees (less than a fist width) to the right and slightly below Regulus, the Lion's heart. Tomorrow night the Moon climbs 8 degrees to the upper left of Regulus.
Now that Mars is noticeable during evening twilight, low in the SE, it draws the attention of incidental skywatchers. Currently the brightest object in the evening, other than the Moon, the planet's brilliance and distinctly orange hue beckon. Notice the similarly colored but fainter star, Antares, a fist to Mars' upper right. The name Antares literally means "rival of Mars," but this time around it is no match for the Red Planet.
Saturn is now up high enough an hour before sunrise that you shouldn't have any trouble finding it. Look any morning in the ENE. Don't confuse the planet with the star Aldebaran which is 4 degrees below Saturn and almost a magnitude fainter. Brilliant Venus, the eye catcher in that part of the sky, is 18 degrees to Saturn's upper right.
The Moon is at First Quarter phase tonight exactly at 11:19 p.m. EDT. Here's an opportunity to see how long before or after the exact moment of First Quarter you can detect the curve of the terminator, the line between light and dark. At 11:19 p.m. it should look perfectly straight.
An hour after sunset the waxing gibbous Moon sits 8 degrees (less than a fist) to the upper right of Spica, the brightest star in Virgo. Spica makes a good reference for bright stars since it is almost exactly 1st magnitude. In actuality it is intrinsically one of the brightest stars in the sky. Its great brilliance is diminished by its distance. Spica lies 260 light years from our solar system.
The Moon is 11 degrees to the upper left of Spica tonight. Almost three times farther, above the Moon and a bit to its right, sits the brighter star Arcturus. These two stars are often associated together in beginning stargazers' minds because of the way they are located. "Follow the arc to Arcturus and speed on to Spica" describes the method of tracing a curved line from the Big Dipper's handle through each of the stars.
The Moon approaches and passes Mars over the next several nights. Tonight Luna is 30 degrees (three fists) to the brilliant planet's upper right. Tomorrow night the Moon is 18 degrees away, and the following night 7 degrees separate the two bodies.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
|