To the reader:
The Skywatcher's Diary for July 2005 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 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
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/
The thinning crescent Moon offers a reason to glance at the early dawn sky over
the next several mornings. Tomorrow Luna hovers 6 degrees (half a fist width) to
the right and slightly above the Pleiades star cluster. Look for the crescent 13
degrees to the lower left of this position the following day at the same time and
another 13 degrees along the same line during twilight on Monday morning, the
4th.
Venus and Mercury are a degree apart low in the west-northwest during evening
twilight. Fainter Mercury is drifting to the left while remaining almost level
with
Venus. Shortly Mercury will begin dropping rapidly away, becoming difficult to see
by mid month. Saturn, currently hard to spot, hangs 8 degrees (not quite a fist)
to
the lower right of Venus. Use binoculars.
Venus and Mercury still mesmerize at dusk. Be sure to bring the binoculars along
tonight while checking on them. The planet pair is passing through the region of
sky occupied by the Beehive or Praesepe star cluster. This sprinkling of faint
stars
is a favorite target of amateur astronomers armed with binoculars or small
telescopes. If the sky is particularly clear tonight, you might be able to detect
some of the "bees" swarming between the two planets.
Early this morning the NASA's Deep Impact spacecraft was scheduled to collide
with Comet Tempel1. Tonight presents the first opportunity most observers in the
Western Hemisphere will have to examine the comet after the impact. As a result
of the collision, the rather dim 9th-magnitude comet is predicted to brighten to
near 6th magnitude -- still too faint for unaided eye or standard binoculars, but
certainly within the range of small telescopes. If you would like to see it for
yourself, visit NASA's Deep Impact website for a finder star chart.
Around 1 a.m. EDT this morning the Earth reaches aphelion. At that moment we
swing farthest from the sun for the year -- about 94,512,000 miles. Should you be
thinking about skipping the sunscreen today, perish that thought. We're only 1.7
percent farther away from Sol than average. And if you still hold the notion that
summer occurs because the sun is closest to us, it's the perfect time to revise
that idea.
The Moon turns New at 8:02 a.m. EDT. You can next catch sight of Luna tomorrow
evening. Look 45 minutes after sunset. At that time the crescent perches 5
degrees (half a fist) above the horizon, just to the right of west-northwest.
Venus,
with Mercury close by, sits 9 degrees to the Moon's upper left. Continue watching
as the Moon descends and the sky darkens.
Mars is easy to spot before dawn because it is now passing through Pisces, one
of the faintest of the zodiac constellations. Just look for the brightest object
in the
southeast an hour before sunup. The 2nd-magnitude star 23 degrees (2 fists) to
the planet's lower right is Diphda, or Beta, in Cetus, the Sea Monster. The Great
Square of Pegasus resides about that same distance to Mars' upper right.
Celestial scenic alert. Soon after sundown the Moon, Venus, and Mercury can be
found cavorting low in the west-northwest. Luna hovers 3 degrees (6 moon
diameters) almost exactly overtop Venus. Mercury hangs 2 degrees to its bright
sibling's lower left. Mercury, now magnitude +0.5, is about 60 times fainter than
Venus (magnitude -3.9).
The waxing crescent Moon rests in Leo tonight, near the neck of the cosmic cat.
Four degrees (8 moon diameters) to Luna's left, and somewhat lower, sits
Regulus, the lion's heart. Venus will pass close to Regulus about 2 weeks from
now. The separation between star and planet is currently 15 degrees (1 1/2 fist
widths). Continue monitoring the Venus-Regulus spread each night that you are
able.
Draco, the Dragon, is a popular but dim constellation in the northern sky. Its
brightest star, 2nd-magnitude Gamma or Eltanin, passes 10 degrees (a fist
width) below overhead about 3 hours after sunset. In England, where the star
climbs even closer to overhead, Eltanin has been known as "Zenith Star." Eltanin
sits within the head of the beast. The Dragon's body hangs below the head. The
tail wraps around the bowl of the Little Dipper then drops between the two
Dippers.
Scorpius is now highest near the end of evening twilight. Bright reddish Antares,
heart of the scorpion, crosses due south about 1 1/2 hours after sundown. This
magnificent constellation is a favorite of serious skywatchers, but can be easily
overlooked by casual observers in temperate latitudes where Scorpius always
remains low in the sky. Southern skywatchers have an advantage since the
scorpion climbs higher with decreasing latitude, reaching the zenith for those 20
to 30 degrees below the equator.
Mercury slips beneath Venus over the next two nights. Look 45 minutes to an hour
after sunset. You will find Venus 7 to 5 degrees (about half a fist) above the
west-
northwest horizon. Mercury dangles 3 degrees below Venus. You may need
binoculars to initially pluck the fainter planet from the sunset glow. Notice the
1st-
magnitude star Regulus, part of Leo, sitting 12 degrees to the upper left of
Venus.
Jupiter and the Moon reside within 4 degrees (8 moon diameters) of one another
tonight. With the two bodies in this close proximity, the brighter Moon serves as
a
marker to help locate Jupiter earlier than might normally be possible. How soon
after sunset (or before) can you spot Jupiter? Try the exercise both with
binoculars
and unaided eye.
If you noticed the Moon last night and again tonight, you might realize that First
Quarter phase occurred sometime between those two occasions. Indeed, the
quarter phase was reached at 11:20 a.m. EDT. The star 4 degrees to Luna's right
tonight is Spica. Jupiter is about 4 times as far (fist and a half) to the Moon's
upper right.
Spica, the Alpha star of the constellation Virgo, lies close to an imaginary line
through the zodiac known as the ecliptic. The ecliptic represents the plane of the
Earth's orbit projected against the stars or, taking a different viewpoint, the
apparent path of the sun through the zodiac. The term "ecliptic" alludes to the
discovery made by early skywatchers that eclipses of the sun and moon occur
along this line.
Eclipses other than solar and lunar can occur on or near the ecliptic, too. The
Moon occasionally passes in front of a bright star or planet, producing an
"eclipse" of that body. The term "occultation," rather than "eclipse," is used to
designate these celestial events. Four of the 1st-magnitude stars lie close
enough to the ecliptic to be occulted by the Moon from time to time. Spica is one
of
those four. A second, Antares, will be occulted tomorrow night.
Observers located on a swath of Earth's surface that includes Mexico, Central
America, northern South America, and the extreme southern and western U.S.
have the opportunity to witness an occultation of the bright star Antares, in
Scorpius. Most of the continental U.S. will see the Moon pass narrowly south of
the star. For times of the event at selected cities, see www.lunar-
occultations.com/iota/bstar/0718zc2366.htm.
Venus and the star Regulus approach one another over the next few days.
Tonight the two objects stand 5 degrees (half a fist) apart, with the star to the
left
and slightly above the planet. Although 1st magnitude, Regulus appears fainter
due to the bright twilight. Use binoculars to locate the star, as needed. Continue
following the movement of Venus and Regulus for the next week. They appear
closest this Friday.
Tonight the Moon sits in the middle of the "teapot" pattern of Sagittarius. Since
the
Moon is only two days from full and quite bright, the shape of the teapot may take
careful scrutiny to detect. The tip of the spout sits 7 degrees (14 moon
diameters)
to Luna's upper right, the top of the lid 4 degrees almost directly above the
Moon,
and the handle 5 degrees to Luna's left.
With the Moon approaching Full tonight, it should rise close to sunset. Watch for
Luna to come up opposite where the sun sets, or near east-southeast. This
"opposite character" of the sun and Full Moon also plays out in their travels
across the sky. The sun currently follows a relatively high arch from east-
northeast to west-northwest, while the Moon's path is relatively low, from east-
southeast to west-southwest.
The Moon turns Full at 7:00 a.m. EDT. In colonial America the Full Moon of July
was known as the Summer Moon or Thunder Moon. Nine hours after reaching
Full, Luna arrives at perigee and the second closest Earth-Moon separation of the
year. Although, technically, the Moon should appear larger than normal at this
time, the effect is subjective and difficult to detect without comparison
measurements. Also, residents on seacoasts should expect greater than
average tides.
Venus slips by Regulus tonight. A little more than a degree (a finger width)
separates the two objects, with the star appearing below and slightly left of the
planet. Forty-five minutes after sunset Venus hovers 7 degrees above the horizon,
slightly north of west. Tomorrow night Regulus rests just less than 2 degrees to
the lower right of Venus. Thereafter the separation increases by about a degree a
day.
Mars is currently passing through the zodiac constellation of Pisces, the Fish, at
the rate of just over a half-degree a day. Tomorrow morning keen observers may
notice the 4th-magnitude star Omicron, in Pisces, a degree directly above Mars.
Look again the following morning to judge Mars' motion. The planet and Pisces
can be found about halfway up in the southeast during dawn.
This time of year after evening twilight, the Milky Way Galaxy bubbles up from the
southern horizon, traverses high across the eastern sky and dips down in the
north. Look south and you stare into the Sagittarius Spiral Arm and the center of
our galaxy. Take an about face and the Perseus Arm comes into view. It's the next
major spiral arm beyond our location and toward the direction sometimes
referred to as the galactic anticenter.
Approximately halfway between the galactic center and anticenter, high in the
east, above where the Summer Triangle lies, we find the direction that our solar
system travels as it orbits around the Milky Way. The star Vega can be used as a
rough guidepost. We travel at the dizzying speed of 500,000 miles per hour, and
yet it takes 200 million years for the solar system to complete one circuit of the
galaxy.
Tomorrow morning the almost-Last-Quarter Moon visits Mars. Luna sits 5
degrees (half a fist) to the upper right of the Red Planet before sunup. The
following morning the Moon skips to the other side of Mars, resting 10 degrees to
the planet's upper left. Mars continues to slowly brighten. It will cross the -1
magnitude threshold at month's end.
The Moon turns Last Quarter at 11:10 p.m. EDT. People often wonder why the
phase is called "quarter" when the Moon appears half lighted. One reason is that
the Moon is three-quarters of the way around its orbit from New Moon and has
one quarter to go before rejoining the sun. You can readily see this by waiting
until
just after sunrise. Point one arm toward the sun and the other to the Moon. The
angle between your arms is 90 degrees, one-quarter circle.
For meteor enthusiasts, the Delta Aquarid meteor shower reaches its peak
tonight. It is not a strong shower, producing a meteor every 4 or 5 minutes on
average. But its peak is broad, lasting a week or so, and overlapping with the
beginning of the well-known Perseid shower. So some observers think of the
Delta Aquarids as the warmup act for the Perseids.
Tomorrow before sunrise look for the waning crescent Moon among the stars of
Taurus. The bright star Aldebaran, marking the eye of the bull, sits 10 degrees (a
fist) below Luna. The Pleiades star cluster, officially part of Taurus, perches 5
degrees to the Moon's upper right. Use binoculars to take a peek at the cluster.
Arcturus, the grand luminary of the spring skies, can still be seen in the west
for a
few hours after sunset. The star belongs to the constellation Bootes, the
Herdsman or Bear Chaser, referring to the Great Bear, Ursa Major. To find
Bootes, look for a skinny kite shape extending about 20 degrees (2 fists) to the
upper right of Arcturus.
Arcturus has been a favored star from earliest times and likely was one of the
first
to be named. Early on the star name was also used to identify the constellation, a
common practice back then. It also was frequently associated with the celestial
bear. "Arktos" is the Greek name for "bear." Modern astrophysics tells us that
Arcturus is a giant orange star. It is cooler than our sun but considerably
brighter
because of its size.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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