August 2002 Sky from Keeble Observatory
With the rocket's bright exhaust plume brightening the pre-dawn sky, NASA's latest
comet probe was successfully launched from Cape Canaveral at 2:43 am on the 3rd
of July. CONTOUR (Comet Nucleus TOUR) was placed by its Boeing
Delta II launch vehicle into an eccentric 42-hour elliptical orbit about Earth,
from where it will be boosted into solar orbit on August 15, on its way to rendezvous
with two comets in 2003 and 2006. The ambitious Discovery class mission will cost
a total of $159 million, and is expected to provide our most detailed ever knowledge
of comets - which are understood to be remnants of the formation of our Solar System
some 4.6 billion years ago.
While in its phasing orbit - which ranges from a mere 124 miles at its closest approach
out to over 71,000 miles (200 km - 115,000 km) - the Earth and the two target comets
will shift relative positions until they are aligned for a simple slingshot trajectory
to carry CONTOUR past its targeted comets. On the 15th of August, somewhere over
the Indian Ocean, the probe's solid rocket booster will initiate a 50 second burn
to carry the spacecraft away from Earth. Instrument check-out will take place over
the following months, until mid-October, when the spacecraft will be powered down
for its cruise mode, with only communications and guidance systems active.
Sometime in mid-July of 2003 all systems will be brought on line for its encounter
with Comet Enke on 2003 November 12. A full array of cameras and spectrometers
will study the comet nucleus from as close as 100 km (62 miles). The environs of
an active comet are hazardous, with rock and dust accompanying the vented gas from
the comet, at speeds of tens of kilometers per second. The probe is protected by
a 10 inch thick layer of Kevlar armor - the same material used for bullet proof
body armor for police and military. After the first flyby, the probe will return
to cruise mode until its encounter with Comet Schwassmann-Wachmann 3 in 2006.
The mission profile is designed with sufficient flexibility that CONTOUR could be
retargeted should some newly discovered comet (a la Hale-Bopp of recent memory)
happen to make an appearance in the inner solar system.
Lunar phases for August: Last Quarter at 6:22 am on the 1st (and again on
the 30th at 10:31 pm); New Moon at 3:25 pm on the 8th; First Quarter on the 15th
at 6:12 am; Full Moon on the 22nd at 6:29 pm.
The Perseid meteor shower will peak 10-13 August. Best viewing will be in
the pre-dawn on the 12th, but expect increased numbers of shooting stars for about
a week around those dates. Get away from city and town lights for the best chance
of seeing this annual light show.
Early evening planet viewers will have to content themselves with Venus this
month. It's still the brightest thing emerging from the western twilight. Mercury
is particularly low on the horizon, and not likely to be seen in the twilight before
it sets. Jupiter and Saturn can be seen in the pre-dawn, to the east and
east southeast. Saturn rises about 3 hours before dawn at the beginning of the month,
and is high in the sky in Taurus, where it will appear as the brightest star
in that constellation. Jupiter emerges from the Sun's glare, and climbs higher at
dawn as the month advances. Saturn stays about 40 degrees ahead of Jupiter on the
sky for the whole month. Overhead at about 10:00 pm at mid-month you will see the
bright star Vega close to zenith. It marks the western end of a triangle
of bright stars - Deneb is a bit to the northeast, Altair to the southeast.
Deneb is at the tail of the constellation Cygnus (the Swan), which marks
the general direction in space towards which Earth and Sun are orbiting in the Galaxy.
The center of the Galaxy lies to the south, in the constellation Sagittarius. To
the southwest you will see the bright red star Antares, in the constellation
Scorpio. From Vega to the west, you will see the irregular square of Hercules,
and closer to the horizon the bright star Arcturus. To the northwest is the
big dipper of Ursa Major. The pointer stars at the end of the bowl of the
dipper direct your eyes to Polaris, which is approximately due north.
For your own monthly star chart, you can direct your web browser to
http://www.skymaps.com. You will find extensive descriptions of what's worth
looking for, and you can download and print a single copy for your personal use.