October 2004 Sky from the Keeble Observatory
This month's celestial ballet will bring two eclipses - though only one will be
visible from the center of the universe! On the 13th, the Moon will slip partially
in front of the Sun, casting a shadow visible from parts of Asia and Alaska, starting
at about sunset in the 49th state. The Moon is 400 times smaller than the Sun, which
lies 400 times further away. That makes them about the same size on the sky. Although
the Moon's orbit is tilted relative to the Sun's path through the sky, it crosses
the ecliptic at two points in the sky called "nodes." Sometimes the Sun
and Moon will both be at the same node at the same time ... that causes a solar
eclipse. Exact alignment causes a total eclipse, inexact alignments within ¼
degree will cause partial eclipses.
However, the Moon's shadow on Earth is relatively small, less than a thousand miles
across, so not everybody gets to see the eclipse. Earth's shadow at the Moon's distance
is nearly three thousand miles across, so that when Sun and Moon are at opposite
nodes, there is a greater chance that the Moon will actually pass through the shadow.
Also, everybody between the sunset and sunrise lines on Earth will get a chance
to see the lunar eclipse.
On the 27th, the Moon will slip into the outer part of Earth's shadow (the penumbra)
starting at about 7:03 pm, and will make contact with the inner, darker part of
the shadow (the umbra) at 8:18. The eclipse will be total at about 9:33. The Moon
will still be visible, but will appear dark and somewhat red - imagine the refracted
light of a million sunsets and sunrises. It begins emerging from the umbra at 10:48,
and will be fully in the penumbra at 11:53. The eclipse ends at 1:03 am on the 28th.
No special equipment is needed to view a lunar eclipse ... binoculars will bring
out more details, but you can see the shadow without them!
Lunar phases for October: Last Quarter on the 6th, at 6:12 am; New Moon at 10:47
pm, on the 13th; First Quarter on the 20th, at 5:59 pm; Full Moon on the 27th, at
Evening skies are devoid of planets until Mercury returns after mid-month. However,
it will remain difficult viewing, as the plane of the ecliptic makes a shallow angle
with the horizon, keeping it in the haze and clutter. Pre-dawn skies offer more
promise, with 5 planets at the beginning of the month, down to four at the end.
The good news is that Mars and Jupiter will be getting higher at sunrise as the
month goes on. On the first, you may be unable to see Mercury, Mars, and Jupiter
within 7 degrees of the Sun. Fortunately, the ecliptic makes a steep angle with
the horizon in the morning, so Venus and Saturn are high and bright at 40 and 67
degrees, respectively. By month's end Mars will be 15 degrees above the horizon
at sunrise, with Jupiter at 30 degrees, competing with Venus at 33 degrees ... it
should be quite a sight!
Two hours after sunset we find that Cygnus has slipped about 10 degrees west of
zenith. Its brightest star, Deneb, is now to the northwest of zenith. Cygnus marks
the northeast to southwest plane of our Milky Way Galaxy, and if you shift your
gaze to the southwest end, your eyes will notice a faint but lonely star at the
"head" of the swan (or the foot of the cross). Binoculars will reveal
Albireo as a binary star. A modest telescope will allow you to discern its beautiful
coloring, with one star a brilliant blue, the other a ruddy orange.
Below Cygus lies Vega, in Lyra. Also, seeing doesn't have to be perfect for binoculars
or a small telescope to resolve the "double-double" - the modestly bright
star next to Vega - as a pair of close binaries. Binoculars should enable you, on
a clear moonless night, to pick out the faint Ring Nebula, also in Lyra. The finder
chart below was produced with the software package "Starry Night Pro"
- available from Sienna Software. Starting from Vega, you should be able to "star
hop" through the constellation.
Below Lyra, find the faint irregular square of Hercules. Midway between the two
lower stars, your binoculars may enable you to pick out the globular cluster known
as M 13. This system of some 100,000 stars orbits our Galaxy, looking much like
a swarm of dandelion seeds.
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.