September 2002 Sky from Keeble Observatory
NASA has another embarrassment to deal with - the CONTOUR spacecraft
we highlighted in August has apparently been lost. After the scheduled
burn of the solid booster, the spacecraft's signal was not recovered.
Telescopes identified what appear to be three fragments of the spacecraft
on its predicted trajectory. We'll have more to say once the inquiry
Speaking of embarassment, how embarrassing would it be if you couldn't
find most of the money you knew was in your bank account? That is
somewhat the state of modern cosmology, which has wrestled in recent
decades with what was once known as the missing mass problem.
We had determined from orbits of stars in our own and other galaxies
that the total mass of stars, gas, and dust in those galaxies was
insufficient to account for the observed paths of the stuff we could
see. Also, the inferred and observed motions of galaxies within
clusters also indicated that there was not enough stellar and interstellar
material to account for the observed gravity - i.e. much of the
mass was missing. Actually, it's not missing, but it doesn't emit
or absorb electromagnetic radiation - i.e. light - so it is better
called dark matter. Indeed, the necessary mass would be almost
ten times the observed luminous matter. Some of it, though not
nearly enough to solve the problem, has been detected in the form
of brown dwarfs or free-floating planets, too cool to emit detectable
radiation, but which sometimes block the light from more distant
To make the situation even more embarrassing, there are firm theoretical
arguments to suggest that there couldn't be that much normal matter
in the universe. But, the total mass of normal matter both observed
and inferred is only about 20% of what theory tells us to expect.
A substantial part of what the universe is made of has to be in
the form of exotic dark matter - curious particles hinted at by
some versions of the standard model of fundamental particles.
Even more curious, most of the universe seems to consist of a mysterious
dark energy which is accelerating the universal expansion. We'll
say more about these next month.
Recall that I said above that we hadn't been able to observe all
the normal matter that our theories told us to expect. The good
news is that researchers using the Chandra X-Ray Observatory have
found the missing normal matter. Where is it? It's not in galaxies,
but in the vast space between them. And, it's very hot - 300,000
to 5 million degrees Kelvin. Observing distant quasars, Chandra
observers from the Harvard-Smithsonian Center for Astrophysics (CfA)
and Ohio State measured the absorption of x-rays by the hot gas,
primarily looking for absorption by highly ionized oxygen and other
heavier elements. The amount of absorption at specific wavelengths
provides a probe of the temperature and density of the intervening
material. Extrapolating results from a handful of quasars to the
whole sky tells us that the intergalactic medium is filled with
filaments of this hot gas - with more mass than all the galaxies
Other observers from the University of Michigan flipped the procedure
around, using the absorption of x-rays emitted by the hot intergalactic
gas absorbed by passing through intervening galaxies. Analysis of
their results gives similar answers for the distribution and temperature
of the gas filaments.
Lunar phases for September: New Moon on the 6th, at 11:10 pm; First
Quarter on the 13th, at 2:08 pm; Full Moon on the 21st, at 9:59
am; Last Quarter on the 29th, at 1:03 pm.
Evening planet watchers will have to be content with Venus, brilliant
but low above the southwest horizon for about an hour after sunset.
Mercury sets even earlier, and is not likely to be visible through
clutter and haze. Jupiter and Saturn are visible in the pre-dawn
sky, east to east-southeast.
An overhead view about an hour after sunset finds Vega, in the
constellation Lyra, almost at zenith. During the first and last
weeks of the month, there should be little moonlight to interfere
with seeing the Ring Nebula in the same constellation with binoculars
or a small telescope. Near Vega you can also resolve the double
double as a binary with binoculars. A modest telescope and good
seeing will permit you to notice this as a pair of binaries. The
systems are actually gravitationally bound - four stars in an elegant
celestial dance. To the east of Vega, note the familiar cross shape
of Cygnus. The bright star at the tail of the Swan is Deneb. The
star at the other end of the pattern is Albireo - a small telescope
reveals this as a binary, as well, with the two stars of strikingly
different colors (one blue, one orange, which means they have different
surface temperatures). A bit to the south we find Altair, in the
constellation Aquila (the Eagle). The three bright overhead stars
(Vega, Deneb, Altair) are sure signs that autumn is coming. On the
23rd the Sun crosses the celestial equator heading south, an event
marked as the Autumnal Equinox. Only on this day does the Sun actually
rise due East and set due West. As the year continues toward December's
Winter Solstice, the sunrise and sunset points will drift to the
south, making fewer hours of daylight and longer nights. Returning
attention to Deneb, follow the Milky Way to the northeast. You'll
notice a crooked W shape above the horizon - that's Casseiopeia.
A larger triangle of bright stars is to the west. Again anchored
by Vega, sweep your vision west through Hercules to bright Arcturus,
in Bootes. To the southwest is bright red Antares, in Scorpio. The
northwest horizon is marked by Ursa Major, the familiar Big Dipper.
Another binary is found in the middle of the handle - the Mizar/Alcor
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.