October 2003 Sky from the Keeble Observatory
I know that we've all had enough of hurricanes and tornadoes.
But, the recent demise of Galileo, intentionally crashed into Jupiter
on the 21st of September to ensure that it would not contaminate
Europa, reminded me that wind systems seem the norm for all planets
If Earth did not rotate, the wind patterns would be simple. Hot
air would rise at the sub solar point, and be replaced by cooler
air coming in from the cool shaded side of the planet. The sub solar
point would travel around the tropics once a year, so the equatorial
regions would be generally warmer than the poles. The overall pattern
would have surface winds blowing from pole to equator, with upper
altitude winds blowing the other way. We actually find this Hadley
circulation near the surface on slowly rotating Venus, which has
a dense carbon-dioxide atmosphere.
For our atmosphere, the rotation of the Earth once each day gives
rise to an additional forcing term, called the Coriolis effect,
which causes moving parcels of air to turn to the right in the northern
hemisphere, and to the left south of the equator. This gives rise
to the characteristic clockwise circulation around northern high-pressure
systems, and counterclockwise around the lows (the H an L that you
see on weather maps). Coriolis forces also break the Hadley circulation
into equatorial and polar belts where the surface winds blow from
the east, and mid-latitudes where the prevailing winds are from
the west. The complex interplay of prevailing winds and circulating
highs and lows give rise to much of the weather we have come recently
Next month I'll say more about Earth's weather, and how it compares
with that on the other planets in our solar system.
Lunar phases for 2003 October: First Quarter on the 2nd, at 3:10
pm; Full on the 10th, at 3:29 am; Last Quarter on the 18th, at 8:32
am; New Moon on the 25th, at 8:51 am. All of these times are Eastern
Daylight Time. We return to Standard Time (fall back) on the 26th
- to celebrate, the Moon gives us another First Quarter on the 31st,
this one at 11:26 pm EST.
Mercury is a morning star at the beginning of the month, but
moves back into the glare of the Sun by mid-month. At sunset, you
may notice a bright star low to the southwest; that's Venus. Mars
remains a bright red presence to the south, not as spectacular as
early September, but still impressive. Jupiter and Saturn rise late
(Saturn about an hour after midnight, Jupiter several hours later)
and are better pre-dawn targets.
Cygnus is almost directly overhead about two hours after sunset,
marking the plane of the Milky Way, which bisects the sky from northeast
to southwest. The bright star alpha Cygni (Deneb) is closest to
zenith, with Albireo to the southwest. Vega toward the west, and
Altair to the south mark with Deneb the Winter Triangle. Sweeping
binoculars from Vega towards Arcturus to the west-northwest will
take you through the constellation Hercules. On a clear, moonless
night you may notice the diffuse globular cluster in that constellation.
Globular clusters are compact groups of up to a million old stars,
collectively orbiting the Galaxy. A similar binocular sweep from
Deneb toward the east-northeast will take you through the constellation
Andromeda and allow you to view the Andromeda Galaxy. This object
is not part of our Galaxy, rather is part of the Local Group; it
lies some two million light years distant. Ursa Major is low to
the north-northwest, probably too low on the horizon to see through
the haze and ground clutter. From Deneb to the southeast, your view
will take you out of the plane of the Galaxy, into regions sparsely
populated by nearby stars. These constellations seem widely spaced
and empty when compared to the rich star fields along the plane
of the Milky Way.
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.