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
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
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 Leo.
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.