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
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 11:07 pm.
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
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
For your own monthly star chart, you can direct your web browser
You will find extensive descriptions of what's worth looking for,
and you can download and print a single copy for your personal use.