September 2008 Sky from the Keeble Observatory
Last month we started a series of essays, loosely titled “How do they know that?”
However, before continuing next month in that vein, let me bring you up to date
on some recent news from Mars.
Mars Phoenix researchers have confirmed the presence of water ice inches
beneath the Martian surface. They scooped a sample into one of the probe’s ovens,
and heated it. The sample melted at the right temperature, and vaporized at the
right temperature, and the gas given off was water vapor. Expect about another month
or so of data, as the northern hemisphere of Mars is approaching winter, and the
probe will be unable to operate without solar energy.
The Mars rovers, Spirit and Opportunity, continue to function (over
four years beyond their design “warranty” of 90 days operation)! Spirit has been
in near-hibernation mode through the southern hemisphere winter, but power levels
are rising. Hopefully the coming of spring will also bring the occasional wind to
blow some of the dust off the solar panels. Opportunity has finished its foray into
Victoria Crater, and has started the attempt to climb back out. It’s showing its
age, as the instrument arm cannot be properly folded back into standby position,
and one of the wheel motors is showing signs that it may fail. It’s the later situation
that pushed the decision to leave the crater, because they need all six wheels operating
to make the climb. Once back on level ground, experience with a similarly failed
wheel motor on Spirit tells us that they can operate successfully there.
Next month I’ll return to the question of how we know the distance to the Sun. (Hint:
it’s more about triangles!)
Lunar phases for September: First Quarter on the 7th, at 10:04
am; Full Moon on the 15th, at 5:13 am; Last Quarter on the 22nd,
at 1:04 am; New Moon on the 29th, at 4:12 am.
Pre-dawn planet watchers … may want to sleep in or stay up late early in September,
because Jupiter is the only planet visible, and it sets about five hours before
sunrise! Saturn joins the pre-dawn twilight around midmonth. Look for it low to
the east, eventually rising more than an hour before the Sun clears the horizon
by the end of the month.
If you have a clear horizon toward sunset, you should see Mars, Mercury, and Venus
grouped about 10 – 15 degrees to the west-southwest early in the month. Mercury
will move quickest relative the Sun, and by month’s end it’s lost in horizon clutter
at twilight. Mars stays about the same relative position, as Venus climbs slowly
above away to the left, setting about an hour after sunset.
An overhead view about 3 hours after sunset finds the Milky Way bisecting the sky
from northeast to southwest. The constellation Cygnus is almost at zenith, marked
by the bright star Deneb, which is just north of the overhead point on the sky.
At this time of year it is easy to envision namesake, the swan. Deneb marks the
tail of the swan, with the faint but beautiful binary Albireo at its head. Although
not nearly as bright as Deneb, this star is easy to pick out because it has no nearby
bright neighbors to confuse the eye. With a small telescope you can resolve the
pair, with one a bright orange and the other a deep blue color. About 15 degrees
toward the west from zenith is the bright blue star Vega, in the constellation Lyra,
and to the south lies Altair, in Aquila. These three stars will likely be the first
to emerge from evening twilight, accompanied by bright Jupiter to the south-southeast,
about 25 degrees above the horizon. To the northeast, the crooked W shape of Cassiopeia
is tilted slightly backward. Below and to the right you may see the relatively nearby
Andromeda Galaxy – best seen on a moonless night, and with averted rather than direct
vision. To the northwest is the familiar shape of the Big Dipper – formally Ursa
Major – low above the horizon, with the two stars at the end of the “bowl” pointing
up toward Polaris, the Pole Star. Polaris is not extremely bright, but its importance
lies with its position almost directly over Earth’s North Pole. From the northern
hemisphere, this star is always above the horizon, so it’s a useful navigation tool.
The angular separation between Polaris and the northern horizon is equal to the
observer’s latitude. Finding longitude requires an accurate clock, but that’s a
tale for another month.