May 2008 Sky from the Keeble Observatory
Mars, again! If this column seems frequently to return to Mars, there is good reason.
Roughly every 26 months there is a “launch window” for sending spacecraft to the
Red Planet on the most energy-efficient (i.e. cheapest!) trajectory. That window
opened again last August, and on 2007 August 4 the Phoenix Mars Lander left Cape
Canaveral atop a Delta rocket. The robotic probe will, if all goes well, execute
a powered soft landing on the high northern plains of Mar on May 25th.
In ancient mythology (and Harry Potter novels!) the Phoenix is a bird which is reborn
from the ashes of its own fiery destruction. Budget woes and technical glitches
earlier in this decade led to the demise of two planned Mars missions, the Mars
Polar Lander and the Mars Surveyor 2001. Both spacecraft were nearly complete, and
their components were essentially mothballed.
Those components have been reassembled into the Phoenix, which will dig into the
top soil layers to analyze the underlying ice. Both soil and the underlying ice
will be analyzed in a variety of remote science experiments on the lander. Specifically,
the project team will attempt to answer two key questions: First, are current conditions
on Mars capable of supporting “extremophile” life forms, similar to terrestrial
bacteria found living in Earth’s arctic ice? These bacteria form dormant spores,
and can remain so for perhaps millions of years until conditions are favorable for
their reactivation. Second, is there evidence indicating that such life ever existed
in the Martian arctic?
Unlike the current generation of (still operating!) Mars rovers, this will be a
powered descent using hydrazine thrusters to slow the spacecraft’s fall to the surface
once the parachutes are jettisoned. The rovers, you will recall, used airbags and
basically bounced and rolled to their landing sites. One challenge in the chemical
analysis will be to account for the thruster exhaust when analyzing the surface
– they expect it to be contaminated with ammonia and unburned hydrazine.
Lunar phases for May: New Moon on the 5th, at 8:18 am; First Quarter
on the 11th, at 11:47 pm; Full Moon on the 19th, at 11:11
pm; Last Quarter on the 27th, at 11:57 pm.
Predawn sky watchers will have limited viewing targets this month. At sunrise, toward
the east you may be able to pick out Venus, assuming you have a pristine eastern
horizon and no haze. Most likely, it’s too low for easy observing otherwise, and
will settle closer to the Sun as the month passes. It’s pulling ahead in its orbit,
swinging around to the far side of the Sun, and will reappear in the evening skies
late in June. Jupiter begins May to the south at sunrise, about 30 degrees from
the horizon. It will settle lower and to the southwest by month’s end.
Evening viewing is a little better. Saturn is high at sunset all month, beginning
to the south-southeast about 63 degrees above the horizon at the beginning of May.
It’s about five degrees to the east (left) of Regulus, in Leo. Mars is high to the
west at sunset, level with and almost equally spaced with Castor and Pollux in Gemini.
Mars will drift rapidly to the east this month, passing through the “Beehive” cluster
around the 23rd, getting closer to Saturn. Look for them both to the
southwest by the beginning of June. Mercury has emerged as an “evening star” climbing
higher each night for the first two weeks. It will reach “greatest eastward elongation
on the 14th, setting more than an hour after sunset. It will then rapidly
move towards our orbital alignment, appearing closer and closer to the Sun. By the
end of May, Mercury will set only about 20 minutes after the Sun crosses the horizon.
Our overhead view at mid-month, roughly two hours after sunset, finds the direction
toward zenith almost empty of stars. The plane of the Galaxy is coincident with
the horizon, and you will be looking out of the plane toward “galactic north.” The
center of the Milky Way is below the horizon to the south-southeast, in the constellation
Sagittarius. The brightest star to the south is Spica, in the constellation Virgo,
about 40 degrees above the horizon. Arcturus, in Bootes, lies to the southeast at
about 60 degrees elevation, and Regulus is to the southwest at 50 degrees. This
triangle lacks a name, though we might think of it as a “spring triangle.” Vega
and Deneb are to the northeast, low to the horizon, and Altair is below the horizon.
These comprise the “Summer Triangle,” and they will be high in the sky in another
Ursa Major is high to the north, with the “bowl” of the familiar Big Dipper inverted.
From the last star in the “handle,” you can imagine following the extension of the
arc of that asterism to find Arcturus if you haven’t already found it to the southeast.
Directly from that last star in the handle, known as Alkaid, a slow sweep upward
about 5 degrees will bring your binoculars or small telescope to the beautiful galaxy
M51, known as the Whirlpool Galaxy.
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.