Abrams Planetarium Skywatcher's Diary
September 1998
To the reader:
The Skywatcher's Diary for September 1998 has been prepared by
Robert C. Victor. Credit to the author and to
Abrams Planetarium, the
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-t.html
If you would like a printed sample of the September issue, please send a long,
self-addressed stamped envelope to:
September 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
ftp://www.pa.msu.edu/pub/swd/
Two bright planets in evening! Jupiter this month is closer and
brighter than it's been since 1987. On Sept. 1, it rises just south of due
east within 45 minutes after sunset. On Sept. 15, Jupiter is at opposition
and visible all night: Look in ESE at nightfall, high in S in middle of
night, and in WSW at dawn's first light. At month's end, Jupiter is low
in ESE at dusk. Saturn rises during the evening, about 2-1/2 hours after
sunset on Sept. 1, to just over an hour after sunset on Sept. 30. It
appears as a bright "star" rising north of east, far lower left of Jupiter.
For rest of the night, Saturn trails Jupiter across the sky, 38 to 41
degrees E of the giant planet and three magnitudes fainter. Diary entries
for Sept. 5-9 describe arrangement of Moon, Jupiter and Saturn at
various times of night.
In early September, all five naked-eye planets can be simultaneously
viewed in morning twilight. Begin looking about one hour before
sunrise, when bright Jupiter is low in WSW, and Saturn is high in
SSW to SW, nearly 40 degrees to Jupiter's upper left. Faint Mars is
some 20 degrees up, just north of due east an hour before sunup.
Brilliant Venus has then just risen. From Sept. 1 to 15, you'll find it 16
to 24 degrees to Mars' lower left. Mercury is very near Venus; during
Sept. 1-8, it closes from 3 degrees to 1.4 degrees to Venus' upper right.
In morning twilight on Sept. 6-8, Venus, Mercury, and the star Regulus
form a very compact grouping, an impressive sight for binoculars. For
details, see Skywatcher's Diary entries below, and diagrams on our
Sept. Sky Calendar.
On Sept. 9 Mercury is 1.0 degree above Venus; on Sept. 10, Mercury
appears 0.5 degree upper left of Venus; on Sept. 11, Mercury passes
just 0.4 degree to Venus' left. Finally, on Sept. 12-15, Mercury widens
from 0.8 degree to 2.6 degrees to Venus' lower left.
Skywatcher's Diary: September 1998
An hour before sunrise these mornings, all five classical naked-eye
planets can be seen simultaneously! Bright Jupiter is in WSW, and
Saturn is in SSW, nearly 40 degrees to Jupiter's upper left. Brilliant
Venus has just risen in ENE (you'll need an unobstructed view). On
Wednesday morning, look for Mercury 3 degrees upper right of Venus,
and dim Mars 14 degrees upper right of Mercury and 21 degrees lower
left of the star Procyon. Mercury sinks closer to Venus each morning,
and on Sept.11 it will pass only 0.4 degree left of the brighter planet as
both traverse the far sides of their orbits. Speedy Mercury will pass on
the far side of the Sun on Sept. 25, and Venus will do so five weeks
later.
The four brightest objects an hour after sunset tonight, in order, are: the
Moon in SSE; Jupiter, very low, just S of E; golden Arcturus in W; and
blue-white Vega, overhead.
An hour before sunrise on Thursday, the four brightest objects, in order,
are: Venus very low in ENE; Jupiter in WSW; blue-white Sirius in SE;
and Mercury, still within 3 degrees to Venus' upper right.
An hour before sunup these mornings, the constellation Orion in
prominent in SE. Look for the pattern, "Three stars in a row, and two
stars above, two below." The three stars in a short line 2.7 degrees long
mark the Hunter's belt. Follow the line of the belt downward to Sirius,
brightest nighttime star. Even brighter is Venus, very low in ENE.
mercury is 2.7 degrees upper right of Venus. Using binoculars,
compare Mercury-Venus separation to the length of Orion's belt. The
other planets visible are Mars 15 degrees upper right of Mercury,
Jupiter in WSW, and Saturn 40 degrees to Jupiter's upper left.
Three hours after sunset, a line from the Moon to Jupiter, some 30
degrees long, extended nearly 40 degrees past Jupiter locates Saturn low
in the east. An hour before sunup on Saturday, the Moon is already set,
but Jupiter and Saturn are still visible in the southwestern sky. Venus
has just risen; look very low, about 15 degrees N of E. Mercury is just
2.5 degrees to Venus' upper right. Using binoculars, can you see fainter
Regulus, heart of Leo, 1.6 degrees below Venus? It gets higher and
easier in coming days. The orbital motion of Earth causes Regulus to
emerge from solar glare early this month and rise higher each morning,
while fast inner planets Mercury and Venus, on far sides of their orbits,
sink past Regulus and lower into eastern twilight glow daily. Binoculars
give best views of a compact gathering of Mercury-Venus-Regulus,
especially striking Sept. 6-8.
An hour after sunset, the Moon, approaching Full, is in ESE, with
Jupiter some 17 degrees to its lower left. On Sunday morning, a deep
penumbral lunar eclipse will be visible everywhere in the U.S. west of a
line from Michigan to the Florida peninsula at 4:10 a.m. PDT (6:10
a.m. CDT) as Moon's northern edge shows slight shading. An hour
before sunup on Sunday, Jupiter is 12 degrees to Moon's upper left.
binoculars show the star Regulus 0.8 degree S (lower right) of Venus,
very low, N of E. Bright Mercury is 2.2 degrees to Venus' upper right.
Mars is 17 degrees upper right of Mercury.
Look hourly from dusk until bedtime and watch for changes in the
Moon's position in relation to nearby bright Jupiter. From lower
Michigan the northern edge of the Moon slips only one degree below
the planet about 4-1/2 hours after sunset. Look for them again at dawn
on Monday. Also on Monday morning, watch the horizon between
ENE and E, for 15 minutes beginning one hour before sunrise.
Binoculars give you a striking view of Venus, Mercury, and Regulus in
a tight triangle less than 2 degrees across! Mercury is 1.8 degrees upper
right of Venus; faint Regulus is 1.2 degrees upper right of Venus and
1.2 degrees lower right of Mercury. Look daily for the rest of this week
and watch for changes.
About an hour after sunset, watch for the Moon rising due east, some
13 degrees to Jupiter's lower left. By dawn they're in WSW, 18 degrees
apart. Using binoculars 60 to 45 minutes before sunrise on Tuesday,
locate the tight triangle of Venus-Mercury-Regulus very low in ENE to
E. Mercury is 1.4 degrees upper right of Venus; Regulus is 1.2 degrees
upper right of Mercury and 2.3 degrees upper right of Venus.
Within two hours after sunset, watch for the Moon rising just north of
east, some 30 degrees to Jupiter's lower left. As the Moon rises higher,
watch for Saturn 10 degrees to its lower left. By dawn on Wednesday,
Moon and Saturn are high in SW and several degrees closer. Aim your
binoculars toward the horizon north of east, about 45 minutes before
sunup Wednesday morning, and you'll catch Mercury just one degree
above Venus. Regulus is 3.5 degrees to Venus' upper right.
Before the Moon rises these evenings, the Milky Way is in excellent
view. Trace its path from Sagittarius in SSW, through the Summer
Triangle overhead, and Cassiopeia and Perseus in NE. Through
binoculars, one of the most impressive Milky Way fields is within the
Summer Triangle, from the center star of the Northern Cross to its
southern tip.
About 2-1/2 hours after sunset tonight, catch the waning gibbous Moon,
just risen, accompanied by Saturn within 6 degrees to its upper right. By
dawn on Thursday, they're 9 degrees apart. Also that morning, note the
star Aldebaran, eye of Taurus, high in SSE some 28 degrees to Moon's
upper left. Check Friday's Diary to see what will happen Saturday
morning. As dawn brightens on Thursday, binoculars show Mercury
just half a degree above Venus.
An hour before sunup on Friday, look high in southern sky for
Aldebaran 13 degrees to Moon's upper left. About 45 to 55 minutes
before sunup, look very low, between ENE and E, for the pair of inner
planets at their closest, as Mercury passes 0.4 degree left of Venus.
You'll need an unobstructed view of the horizon, and binoculars will
help. Can you spot Regulus 6 degrees to the upper right of the pair, and
Mars another 16 degrees upper right of Regulus? Mars and Regulus
will have a close encounter on Oct. 7. The zodiac, or pathway of the
Moon and planets, is well marked, in order, by bright Jupiter low in
WSW, Saturn well up in SW, the Moon, Aldebaran, Mars, Regulus,
and the Venus-Mercury pair.
About four hours after sunset, the Moon, just over half full, has just
risen in ENE. From lower Michigan, the star Aldebaran then appears 2
degrees to Moon's lower left. Around 3:25 a.m. EDT, observers in
lower Michigan will see the Moon's northern edge pass narrowly S of
the star. From parts of southern and eastern U.S., Moon occults or
covers Aldebaran in the predawn hours of Saturday. The event is visible
from all or nearly all of the states of LA MS AL FL GA SC NC VA
MS DE NJ CT RI, and parts of TX AR TN KY WV PA NY MA NH
ME. Here are times (all a.m. on Saturday) for selected cities: San
Antonio TX 1:47-2:10 CDT; Houston 1:46-2:15; Austin 1:51-2:09;
New Orleans 1:44-2:25; Nashville TN 2:12-2:19; Miami 2:35-3:41
EDT; Atlanta 2:55-3:33; Washington DC 3:15-3:43; New York 3:24-
3:47; Boston 3:32-3:51. Some stars in Hyades are covered a few hours
earlier. For more information, check the website of the International
Occultation Timing Association:
http://www.sky.net/~robinson/iotandx.htm
and the map and article on page 112 of the September issue of Sky & Telescope magazine.
Tonight, about 4-1/2 hours after sunset, watch the ENE horizon for the
rising of the Last Quarter Moon which is half full. It has moved 12
degrees east (lower left) of Aldebaran. As twilight brightens on Sunday,
find Aldebaran 15 degrees to Moon's upper right, and Betelgeuse 11
degrees below the Moon. About 45 minutes before sunup, can you still
spot Mercury? By Sunday morning, it has moved 1.4 degrees to Venus'
lower left.
Last call for Mercury? On Monday, 45 minutes before sunup, use
binoculars to look very low, 10 degrees N of E, for Mercury 2 degrees
lower left of Venus. Look for 2nd-magnitude Gamma in Gemini, a
similar distance lower right of a waning crescent Moon.
An hour before sunup on Tuesday, look for the Gemini twins, Castor
4.5 degrees above Pollux, to the Moon's upper left. Pollux is 10 degrees
from the Moon. Procyon, in Canis Minor, the Lesser Dog, is 13
degrees to the Moon's lower right. Mars is in E, 25 degrees to Moon's
lower left. By Thursday morning, Moon will appear within 3 degrees
south of Mars.
Tonight, three bodies, in order Sun-Earth-Jupiter, are arranged in a
straight line in space. As seen from Earth, Jupiter appears at opposition,
or 180 degrees from the Sun, and is visible all night. This alignment of
Sun-Earth-Jupiter occurs each time Earth passes between Jupiter and
the Sun, which happens at intervals of about 13 months (next time: Oct.
23, 1999). Look for brilliant Jupiter in ESE at nightfall, high in S in
middle of night, and in WSW at dawn's first light. Jupiter is now closer
to Earth and brighter (mag. -2.9) than it has been since 1987.
An hour before sunrise on Thursday, face east to see a slender crescent
Moon with earthshine visible on its dark side and Mars within 3 degrees
to Moon's north (upper left). The star Regulus, heart of Leo, is about 12
degrees to their lower left. The Moon will pass closely south (lower
right) of Regulus on Friday morning. On October 7, Mars will finally
pass within a degree north of the star.
An hour before sunup on Friday, find the thin crescent Moon low in
east with the star Regulus closely to its upper left. Mars is 12 degrees
upper right of Regulus. Within 15 minutes, look for Venus 15 degrees
lower left of the star. Look again on Saturday.
If you're in our area this weekend or next, you're welcome to join us at
Abrams Planetarium for Autumn Skies, a preview of this season's
beautiful arrangements of Moon, bright planets and stars. Showtimes
are Fridays and Saturdays at 8:00 p.m., and Sundays at 4:00 p.m.,
September 18-20 and 25-27. Also opening this weekend is our new
family show, Rusty Rocket's Last Blast. It is presented Sundays at 2:30
p.m. For further information and admission prices, please call (517)
355-4672.
Saturday morning will be your last chance to see Venus and the Moon
close together until the early evening of December 19, after Venus has
gone around the far side of the Sun. On Saturday, 40 minutes before
sunup, look for the very slender crescent old Moon very low, a few
degrees north of due east. From lower Michigan, Venus will appear just
2-1/2 degrees lower left of the Moon's illuminated edge. From New
England, the Moon-Venus gap will be nearly 3 degrees; from the West
Coast, less than 1-1/2 degrees. From Hawaii, the Moon's leading bright
edge occults (covers) Venus shortly before sunrise.
Mornings from now through October 3, the Moon will be absent from
the sky 1-1/2 hours before sunrise, providing a good opportunity to
observe the zodiacal light from very dark sites, where there is no
interference from artificial light. Face east just before the first evidence
of morning twilight begins to brighten the sky, and look for a very
large, softly luminous cone of light with its base near the horizon and its
axis near the ecliptic (near Regulus and Mars, extending across Cancer
toward central Gemini). The zodiacal light is caused by the reflection of
sunlight off dust particles which are concentrated in the plane of the
solar system. The dust particles were supplied by comets and by
collisions of asteroids.
The Moon is New at 1:01 p.m. EDT today and is not visible. An hour
before sunup on Monday, in the east, find Mars 10 degrees upper right
of Regulus and closing. They'll be within five degrees apart on Sept. 29,
and just one degree apart on Oct. 7.
Using binoculars about 20 minutes after sunset, look for a very slender
crescent young Moon about 7 degrees south of due west, and 3 or 4
degrees above the horizon (data for lower Michigan). You'll need an
unobstructed view. From southern states, the Moon is higher and easier
to see.
The Moon should be easy for unaided eye tonight, provided the sky is
clear. Forty minutes after sunset, look very low in WSW. Observers in
southern states may see Spica 5 or 6 degrees to Moon's lower left. The
equinox occurs at 1:37 a.m. EDT Wednesday morning as the Sun
stands directly over Earth's equator. For Northern Hemisphere
residents, autumn begins.
Autumn began today at 1:37 a.m. EDT. But the length of day,
measured from sunrise to sunset, continues to exceed 12 hours for three
more days, through Friday. That happens for two reasons: First,
because sunrise and sunset are reckoned by the top edge of the Sun's
disk crossing the ideal horizon, and second, because refraction, or
bending, of incoming sunlight by Earth's atmosphere lifts the Sun's
image. Both effects lengthen the day.
Two hours after sunset, can you see Saturn, low, just north of east, 40
degrees lower left of brilliant Jupiter? In another two hours, Saturn
climbs high enough to allow a clear telescopic view of its rings, now
tipped 16 degrees from edge-on. Look also for Saturn's brightest
satellite, 8th-magnitude Titan, tonight at greatest elongation four ring-
lengths east of the trailing edge of the rings as Saturn and Titan drift
through the field. Titan orbits around Saturn in 16 days, in the same
plane as the rings. Follow this moon around as it passes more closely
north of Saturn on the night of Sept. 28, farthest west on Oct. 2, more
closely south on Oct. 6, and farthest east again on Oct. 10.
A telescope shows Jupiter's four Galilean moons appearing close to the
planet tonight. Io and Callisto appear close together to the west of the
planet; Io is the brighter. Europa appears by itself to the east of the
planet. Jupiter's brightest moon, Ganymede, disappears behind the
western edge of Jupiter at 8:37 p.m. EDT, and emerges from Jupiter's
shadow a short distance east of the planet at 12:52 a.m.
Here's a chance to get a closeup view of Jupiter: Tonight and Saturday,
MSU Observatory is open for public viewing from 9:00 p.m. until
11:00 p.m. if skies are clear, following the 8:00 p.m. showings of
Autumn Skies at Abrams Planetarium.
An hour after sunset, crescent Moon is in SW, with reddish Antares,
heart of the Scorpion, 9 degrees below. Next few nights are good for
using binoculars to see one or more of Jupiter's Galilean moons.
Tonight, can you see all four, arranged two on each side?
Tonight, Jupiter's brightest moon Ganymede, in its one-week orbit,
appears farthest east of the planet. Fainter Callisto is a bit farther out on
the opposite side. Both are easy targets for binoculars tonight. Leisurely
Callisto, taking 17 days to orbit the planet, stays sufficiently far west of
Jupiter for four more nights to remain easy to see.
Rusty Rocket's Last Blast continues Sundays at 2:30 p.m. at Abrams
Planetarium.
This afternoon the Moon is at First Quarter phase and is 90 degrees, or
one-quarter circle east of the Sun. At sunset the Moon is nearly due
south, with its right half illuminated. This is an ideal phase for
observing lunar surface features along the terminator (Moon's day-night
boundary), even with the low magnification of binoculars. At nightfall,
look for the top star of the Teapot of Sagittarius 5 or 6 degrees below
the Moon.
Tonight the Sun rises on the lunar crater Copernicus. Look along the
Moon's terminator (day-night boundary), a little north of the midpoint.
Through binoculars or a small telescope, it appears as a dark circular
hole. As hours pass, high power will show the floor of the crater
becoming increasingly illuminated.
On Thursday 2-1/2 to two hours before sunrise, all three bright outer
planets can still be seen simultaneously. Bright Jupiter is about to set, a
little south of due east. Saturn is high in SW, some 40 degrees upper
left of Jupiter. Mars is low in east, within 4 degrees above Regulus.
Watch Mars-Regulus daily, until they close within one degree on Oct. 7.
