Keeble Observatory
January 2004 Sky from the Keeble Observatory
Last month we wrote about Voyager 1 and promised to say more about
Voyager 2 this month. The latter craft was actually launched first,
on the 20th of August in 1977. A virtual twin of the other craft,
it arrived at Jupiter on July 9th in 1979, four months after Voyager
1. Actually, it's more accurate to say that it flew past Jupiter,
cameras and instruments programmed to image the giant planet and
its moons, studying their surfaces and near-space environment. The
gravitational boost from this flyby gave the probe the correct velocity
to direct it to Saturn, where it made its encounter in August of
1981. (Voyager 1 made its Saturn encounter in November 1980.) Saturn's
gravity was used to fling Voyager farther into the outer solar system,
towards distant Uranus.
During the Saturn encounter the camera platform jammed, requiring
a complete reprogramming of the on-board computer so that the entire
craft could be tilted and swiveled to point the cameras. Also, keep
in mind that the cameras were designed for the light levels at Saturn,
about 1% as bright as sunlight on Earth. Uranus is twice as far
from the Sun, and the light levels are only one fourth those at
Saturn! Exposure times had to be extended, and the pointing accuracy
had to be sufficient to prevent blurring the images. Nonetheless,
Voyager 2 made a successful flyby of Uranus and its moons in January
of 1986, almost nine years after launch! This encounter added enough
speed and redirected the probe to its final planetary encounter
with distant Neptune in August 1988. Neptune, almost thirty times
as far from the Sun as Earth, provided the last gravitational assist
to send the probe below the plane of the solar system and outward
towards interstellar space.
The science return from these two probes is easily as impressive
as the longevity and durability of their 1970s technology. Jupiter
was discovered to possess a thin dusty ring system, mimicking the
brighter and more familiar rings of Saturn. Io was found to be the
most volcanically active object in the solar system. Distant Triton,
orbiting Neptune, was also found to possess a thin atmosphere and
geysers of liquid nitrogen. Lightning and aurora were detected in
the atmospheres of the outer planets, while Uranus' and Neptune's
magnetic fields were found to be mystifyingly off-center and tilted
with respect to the planets' rotation axes. For a more complete
look at the historic and ongoing missions of Voyagers, along with
a treasure trove of spectacular images, go to the JPL website at
www.jpl.nasa.gov.
Lunar phases for January: Full Moon on the 7th, Last Quarter on
the 14th; New Moon on the 21st, First Quarter on the 29th.
January is a good month for evening planet watchers. As the sun
sets, you'll see Venus emerge from twilight to the southwest, about
25 degrees off the horizon early in the month, higher by month's
end. Mar is visible high above the southern horizon. Saturn rises
to the northwest at sunset early in the month, about half way between
Orion and the bright Twins of Gemini. By the end of January, Saturn
emerges from twilight about 25 degrees above the horizon. Jupiter
rises at 10:30 pm on the first, about 8:30 pm by the first of February.
The ecliptic (the path on the sky followed by Sun, Moon, and planets)
is low in the sky during the day, high in the sky at night during
this season. Accordingly, the planets will traverse the night sky
well above the horizon clutter of trees and building, and your view
will be relatively unimpeded by growing light pollution.
About three hours after sunset, the Milky Way divides the sky from
northwest to southeast. To the northwest, you'll see bright Deneb
marking the top of the northern cross of Cygnus. The foot of the
cross is below the horizon. Tracing upward along the plane of the
Galaxy takes you to the irregular M shape of Cassiopeia. Above and
to the left of Cassiopeia, you'll be able on a clear moonless night
to see the Andromeda Galaxy, at more than two million light years,
this is the most distant object visible without a telescope. Almost
at zenith, the bright star in Perseus is called Mirfak (note that
most proper names for stars are Arabic!), though you're more likely
to see Capella in Auriga just to the east, because it's so much
brighter than Mirfak. High to the southeast is bright Aldebaran,
in the constellation Taurus. You're also likely to notice the compact
dipper shape of the Pleiades cluster. Below Taurus is Orion's distinctive
belt. Use binoculars or a small telescope to view the Orion Nebula,
a star-forming region in the sword of Orion. The brightest star
visible (other than the Sun) is Sirius, just below Orion above the
southeast horizon.
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.
Copyright 2004
George Spagna