March 2005 Sky from the Keeble Observatory
Life, at least as we know it here on Earth, depends on the presence
of water; usually liquid, usually at moderate temperatures, but
definitely a requirement. One of the primary mission objectives
for the current fleet of Mars probes and rovers is to seek evidence
for the presence of water, either in the distant past or in some
form in the present.
We have surmised since the 1970s that Mars was once a much warmer,
wetter world than we see today. Currently, the atmosphere is too
thin to allow liquid water – it would boil away into gas.
It’s also too cold, even if the atmosphere would allow liquid,
the temperature for most of the planet during most of its year stays
below freezing. But it was not always so! Extensive now-empty flow
channels are reminiscent of river systems. The landing site for
the Pathfinder/Sojourner probe was clearly a massive flood plain,
tumbling and fracturing rocks, but the floods were long ago, perhaps
billions of years in the past.
Chemical, visible, and geological (areological?) evidence collected
by the Spirit and Opportunity rovers tell us that both landing sites
were once wet. The Opportunity site was once a salty lake bed, with
ripples from shallow water preserved in the rock layers. But those
sites were wet long, long ago.
Recent data from the European Space Agency’s Mars Express
give a tantalizing hint that a lake the size of the North Sea was
present on Mars as recently as 5 million years ago ... practically
yesterday to a planetary astronomer’s eye. Images of large,
flat, fractured plates on a young region known as Elysium Planitia
bear startling resemblance to pack ice floating on the sea. Researchers
conjecture that this 500 by 560 mile region flooded and then rapidly
froze two to five million years ago, possibly due to a catastrophic
flood from a fissure to the northeast known as Cerberus Fossae.
It’s even possible that some of the ice itself is preserved
beneath the dusty landscape.
As with all science, the final verdict will await further data.
The landscape does resemble some fractured lava flows found in Iceland
– we’ll probably have to wait for a lander to give us
a closer look.
(Image courtesy European Space Agency)
Lunar phases for March: Last Quarter on the 3rd, at 12:37 pm; New
Moon at 4:11 am, on the 10th; First Quarter on the 17th, at 2:19
pm; Full Moon on the 25th, at 3:58 pm.
Evening planet watchers will have their best view of Mercury in
the early parts of March. I will be almost twenty degrees above
the setting Sun by midmonth, before rapidly diving back into the
Sun’s glare by the end of the month. Saturn, high above the
eastern horizon at sunset, is still close to Castor and Pollux.
It will match them in brightness, but will show less “twinkle”
since it actually presents a disk rather than a point source. Saturn
sets at about 4:00 am. Jupiter will rise around 9:00 pm early in
March, at sunset by month’s end.
The morning sky finds Jupiter low to the west southwest at sunrise
on the 1st, setting before sunrise later in the month. Mars rises
at about 4:00 am, and can be found low in the southeast at dawn.
Venus is hidden by the Sun’s glare, but returns to the evening
sky next month.
An overhead view about 3 hours after sunset at mid-month finds
Saturn, Castor, and Pollux almost at zenith. Below Gemini, towards
the southwest horizon we can see the familiar shape of Orion. Above
and to the right lies Taurus and the familiar asterism of the Pleiades.
That brilliant blue star to the left of Orion is Sirius, in the
constellation Canis Major. To the northeast the sky is largely vacant,
with only a few bright stars. The familiar shape of Ursa Major is
easily seen high above the horizon, with the “dipper”
standing on its handle. Follow the two stars at the end of the “dipper”
towards Polaris, the pole star. With binoculars, you may still find
Comet Machholz, which will be just above and to the left of Polaris
on the 1st, moving slowly to the east so that it is above and to
the right by the 31st.
For your own monthly star chart, you can direct your web browser
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and you can download and print a single copy for your personal use.