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 Earth.
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 at
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
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
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.