November 2006 Sky from the Keeble Observatory
Five centuries ago, a Polish monk named Nicolas Copernicus started
a revolution. In De revolutionibus orbium coelestrium – On
the Revolution of the Celestial Spheres – he moved the Earth
from its presumed place at the center of creation. Rather, his model
placed the Sun at the center, with the planets (including Earth)
on circular courses about that center. The planets known to him
were Mercury, Venus, Mars, Jupiter, and Saturn, with Mercury and
Venus closer to the Sun, the others’ orbits beyond that of
Those orbits lie close to a plane in space called the ecliptic,
which actually marks the plane of Earth’s orbit, but they
are all inclined slightly to our orbit. For the outer planets, this
means that when on the far side of the Sun, they are seldom in a
direct line behind the Sun, but can be slightly above or below.
When most directly opposite earth, we say that they are in conjunction;
when most directly opposite the Sun as seen from Earth, we say that
they are in opposition. For the inner planets, which can never be
at opposition, we have two conjunctions: inferior, when on the same
side of the Sun as Earth, and superior, when on the other side.
The tilt of the orbit likewise means that it is rare for the planet
to be directly in front or behind the Sun.
When Mercury or Venus actually passes in front of the Sun at inferior
conjunction, we call that event a transit. Venus, whose orbit is
inclined 3.4 degrees to the ecliptic undergoes transits rarely.
The particulars of its orbit cause pairs of transits, separated
by about 8 years, with the pairs separated by over a century. There
have been only seven transits of Venus since the invention of the
telescope! The most recent was in 2004, and the next is in 2012.
Mercury orbits the Sun in a mere 88 days, in an orbit inclined
by about 7 degrees. While favorable alignments are, in principle,
rare events, the short period of the orbit means that we have about
13 transits per century. The next one is November 8 – and
it should be observable from Central Virginia, starting at 2:12
pm EST. It will cross the Sun from the lower left quadrant to the
upper right, though the transit will end after sunset.
Now, some serious cautions: Do not look directly at the Sun! In
fact, because Mercury is almost 200 times smaller than the Sun,
your only hope of seeing anything is with a telescope with appropriate
solar filters and a magnification of 50-100. Binoculars won’t
help, nor will the usual technique of making a pinhole camera. The
early stages of the transit can be observed from the Keeble Observatory,
so we will open for public viewing at 2:00 pm on Wednesday 2006
November 8. We'll likely lose the Sun in the trees by 3:30.
For further information about this transit and about transits in
general, NASA’s Goddard Space Flight Center has a web page
Lunar phases for November: Full Moon at 7:58 am,
on the 5th; Last Quarter on the 12th, at 12:45 pm; New Moon on the
20th, at 5:18 pm, and First Quarter on the 28th, at 1:19 am.
Saturn rises about an hour after midnight, so is a prime candidate
for pre-dawn viewing. Look for it high to the south-southeast before
sunrise. By month’s end, it will be rising before midnight.
Mercury and Jupiter return to the early morning sky. Late in the
month look for Mercury rising about an hour before the Sun, with
Jupiter following about a half-hour later. If you have a clear view
to the southeast, look for Mercury 15 degrees from the horizon,
with Jupiter bright and below that. Jupiter and Mercury are both
going through conjunction with the Sun this month. Mercury on the
8th will be at inferior conjunction (between Earth and Sun), while
Jupiter will line up on the far side of the Sun on the 21st. As
indicated above, Mercury will transit the visible face of the Sun,
starting about 2:15 pm on the 8th.
Looking toward zenith two hours after sunset at mid-month, we find
the Milky Way dividing the sky roughly northeast to southwest. The
bright stars that were almost directly overhead last month have
now shifted to the west. Deneb is about 20 degrees from zenith,
and Vega is another 20 degrees below that. In binoculars or a small
telescope, you can see a few modestly bright stars in the vicinity
of Vega. About 2 degrees above and to the left lies epsilon Lyrae,
also known as the “double double.” This is a pair of
closely spaced binaries – with a modest telescope you may
be able to resolve the narrow pairs, but binoculars should allow
you to see the wider pairing. Sweeping about 6 degrees to the left
of Vega, you will see two stars, separated by about 2 degrees, one
above and slightly to the left of the other. A little less than
halfway between these two stars lies the Ring Nebula. This is the
remnant of a star once much like the Sun which has ejected its outer
layers. It’s a challenging target to find when skies are hazy
or if the Moon is out, but it’s worth the effort.
If we turn our attention east of zenith, we find that Andromeda
is now high above the horizon. Locate Cassiopeia’s familiar
W shape to the northeast, now tipped on its “left side.”
Follow a line through those two stars, upward and to the right,
and you’ll find the faint patch of the Andromeda Galaxy, some
2 million light years distant.
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.