January 2003 Sky from the Keeble Observatory
Looking at the night sky should invoke a sense of wonder. Even
the psalmist comments on their transcendent beauty, and wonders
how a Creator of the Moon and star could care about humanity - read
Psalm 8 for yourself! Wonder is only a small step from curiosity,
and curiosity combined with cleverness has led to the development
of scientific instruments to help satisfy that curiosity. The premier
scientific instrument of the astronomer since the time of Galileo
(early 17th Century) has been the telescope. But, just what does
a telescope do?
Under the dome of the Keeble Observatory is a telescope, which
has been in use since 1966. (The Observatory building itself dates
to 1960.) This particular telescope is of the type known as a Cassegrain
reflector. This is the basic design for most modern astronomical
telescopes, including the giant 10-meter twin Keck telescopes on
Mauna Kea and the orbiting Hubble Space Telescope. The heart of
the instrument is a 12 diameter mirror at the back end of the
telescope, which gathers and focuses light. The amount of light
which can be collected depends on the area of the mirror, this mirror
should be compared with the light collected by your own eye - which
has a dark-adapted pupil about a third of an inch in diameter. Since
the area is proportional to the square of the diameter, we calculate
that the Keeble telescope collects over 1000 times as much light
as your unaided eye - which means that we can see things 1000 times
fainter. A small secondary mirror at the front end of the telescope
reflects the focused light back through a hole in the center of
the primary mirror.
Notice that we've said nothing about magnification, which is what
most people think of as the main characteristic of a telescope!
Magnification can be changed by changing the eyepiece used with
the telescope - shorter focal length on the eyepiece gives increased
magnification. For public viewing, we typically work at a magnification
of about 100. For serious work, we can replace the eyepiece (and
the viewer's eye) with a camera or spectrometer. We've virtually
abandoned traditional film for electronics, using a so-called CCD
camera to record images. Since the camera gives us direct digital
access to the intensity of the collected light, it is possible to
thoroughly analyze the data as well as generating images.
Next month we'll discuss the other telescope at the Keeble Observatory,
the 3-meter Center of the Universe Radio Telescope which sits
next to the dome.
Lunar phases for January: New Moon on the 2nd at 5:24 pm; First
Quarter on the 10th at 8:16 am; Full Moon on the 18th at 5:48 am;
Last quarter on the 25th at 3:34 am.
Earth will be at perihelion (closest to the Sun) on the 4th. It
will still be cold here, because the seasons are driven not by distance
from the Sun but by the tilt of Earth's axis. Northern hemisphere
winter finds the Sun low in our sky because the axis is tilted with
the north away from the Sun. The good news is that, because we're
near perihelion the winter season is shorter for us than summer,
when we're near aphelion.
Saturn is already in the SE sky at sunset, so this is another good
month to look for the ringed planet virtually all night long. Mercury
starts the month in the evening sky at mid-month, but it will be
low on the horizon and not easy to pick out from ground clutter
before it sets. It moves to the morning sky by mid-month, getting
higher as we move toward February. Jupiter rises about two hours
after sunset, and follows Saturn across the southern sky.
Venus remains brilliant in the predawn sky, high to the southeast,
near Mars. Mars moves higher as the month progresses. Jupiter and
Saturn as good morning objects. Look for Venus and Mars about 30
degrees off the southeast horizon at sunrise. By the end of the
month, look for an evenly spaced display from Sun, Mercury, Venus,
Looking overhead at mid-month, about three hours after sunset,
we see the Milky Way dividing the sky from southeast to northwest.
The brightest stars near zenith are Capella and Elnath in the constellation
Auriga just to the east, Mirfak in Perseus to the northwest, and
Aldebaran in Taurus to the south. Orion is high and magnificent
to the southeast, followed by bright Sirius. Castor and Pollux in
Gemini are high to the east, with Regulus rising in the constellation
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.