Keeble Observatory
April 2004 Sky from the Keeble Observatory
Astronomy sometimes seems the hectic science. Ironically so, as
the sky serenely turns overhead, the daily and yearly patterns evoke
a sense of calm. Yet, the news and new information arrive almost
in a flood at times, and these are such times.
In the past month we have learned more from our Mars rovers. Beyond
the stark images from the red, rubble-strewn landing sites, we now
have firm evidence that the Opportunity landing site, known as Meridiani
Planum, was once under water. Mineral evidence is compelling, but
even stronger inferences are drawn from erosion patterns on layered
rocks themselves. What we seem to be looking at is sediment deposited
at the shore of a shallow, briny lake or sea. The erosion patterns
suggest wave action, with water flowing at perhaps several miles
per hour. Investigators delayed nearly a month in making the announcement
of their findings, so that they could consult coastal geologists
not working on the NASA project.
Those enigmatic spherical deposits found by Opportunity, whimsically
dubbed blueberries - though they're not really blue, rather gray,
but approximately the right size for blueberries - have now been
identified as being composed of the iron-rich mineral, hematite.
On Earth, hematite forms in the presence of standing water. Both
rovers will be sent on long traverses from their present locations.
Opportunity will attempt to reach a nearby crater, somewhat larger
than the small "Eagle" crater where it landed. Spirit
will be directed towards the "Columbia Hills" to examine
a geologically (Areologically?) different regime.
Hubble Space Telescope unveiled its deepest yet view of the Universe.
The "Ultra Deep Field" represents an accumulated 11-day
exposure with the high resolution Survey Camera. Directed at an
"empty" patch of sky no bigger than a grain of sand held
at arm's length, the image reveals galaxies that formed when the
Universe was less than a billion years old.
Observers using the venerable 5-meter telescope at Palomar Observatory
have identified the most distant object yet confirmed as part of
our solar system. Dubbed Sedna, after an Inuit deity, this newly
found member of our Sun's family lies nearly twice as far as Pluto.
It's a little smaller than Pluto, a lot redder, and is nearing its
closest approach to the Sun on an extended elliptical orbit. Its
orbital period is over 10,000 years ... carrying it nearly 1000
times as far from the Sun as we live! Adding yet another object
to the catalog of "trans-Neptunian" objects raises again
the call for "downgrading" Pluto from its historical designation
as a planet. It seems to be just the largest and first discovered
of an entire class.
Lunar phases for April: Full Moon on the 5th, at 4:03 pm EDT (don't
forget to turn your clocks ahead on Sunday!); Last Quarter on the
11th, at 8:46 am; New Moon on the 19th, at 8:21 pm; First Quarter
on the 28th, at 12:32 am.
April is still a pretty good month for evening planet watchers,
though we lose Mercury into the Sun's glare by mid-month. As the
sky emerges in the evening twilight, Venus will be the brightest
object to the west. It will be lower in the sky than last month,
but you can watch it for several hours until it disappears into
the horizon clutter and haze. Mars is seen above and to the left
of Venus, a pale orange in contrast to the brilliant white of Venus.
Venus is catching up to us in its orbit, and will lie directly in
front of the Sun in early June. (This rare event, known as a "transit,"
will not be visible from central Virginia.) This month will see
Venus' waning crescent in a small telescope. Saturn is about 50
degrees above the western horizon at sunset, its rings remain a
spectacular sight in a small telescope. Jupiter emerges from twilight
high to the southeast. An imaginary line through these four planets
marks the plane of our solar system, which is slightly tilted relative
to the Moon's orbit around Earth. Nevertheless, you'll see the Moon
pass close to these planets as the month advances ... near Jupiter
on the 2nd, passing Venus and Mars on the 22nd and 23rd, Saturn
on the 25th, and then back to Jupiter on the 30th.
An overhead view about two hours after sunset finds nothing prominent
at zenith (the point in the sky directly overhead). The bright "twins"
of Castor and Pollux are now to the west of zenith, and Leo is to
the south. Towards the north we see the inverted dipper of Ursa
Major almost at zenith. And, to the east, the sky appears almost
empty except for the bright stars Arcturus in Bootes, and Spice
to the southeast in Virgo. Orion bids adieu for another season,
as it settles below the western horizon. The Milky Way arcs low
from north to southwest ... crossing above the western horizon between
Orion and Gemini. A few hours later, the plane of our Galaxy will
nearly match the 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