July 2005 Sky from the Keeble Observatory
Two probes are currently of interest. One fizzled. The other may
provide us with some fireworks for the 4th of July!
Cosmos 1 was intended as an orbital test of a “solar sail.”
Launched from a Russian submarine on a converted ballistic missile,
the satellite was to deploy a set of reflective vanes which would
use the pressure of sunlight in place of thrusters to change its
orbit. The project was a joint undertaking by Russia and the United
States, with substantial private funding from the Planetary Society.
Unfortunately, the booster failed about 83 seconds after launch,
and the mission crashed into the Arctic Ocean.
Deep Impact is a comet probe, on track as this is written to fly
by the comet Tempel 1 on July 4th. Actually, only part of the probe
will fly by. The rest will crash into the comet’s surface
at 23,000 miles per hour. The goal is to find out what the interior
composition and structure of a comet are really like.
The best current model is to consider a comet nucleus to be a “dirty
snow ball,” mostly ices of water, ammonia, methane, etc. The
rest is thought to be an aggregate of dust and gravel. We don’t
know for sure what will actually happen, except that there is zero
chance the collision will send the comet careening into a collision
with Earth. The probe is roughly a half-ton, about a meter tall
and a meter in diameter. The nucleus of Tempel 1 is roughly shaped
like a 14 km long potato.
On the 3rd of July the impactor is scheduled to separate from the
main probe. On board computers will steer it into the path of the
comet nucleus while its on-board cameras return images of its target.
The main part of the probe will pass 500 km from the comet, while
its cameras and other instruments monitor the collision and its
aftermath. The chemical composition of the vaporized comet material,
the size and depth of the crater, and coordinated observations with
ground-based observatories and the Hubble Space Telescope will all
be used to analyze the nature of the target. If there is more rock
than ice, the crater may be much smaller than the football field
size some are predicting. If the comet lacks structural integrity,
the probe could blast all the way through without leaving a crater
Lunar phases for July: New Moon at 8:02 am, on the 6th; First Quarter
on the 14th, at 11:20 am; Full Moon on the 21st, at 7:00 am; and
Last Quarter on the 27th at 11:19 pm.
Earth is at aphelion – farthest distance from the Sun - on
the 5th, about 152 million kilometers (95 million miles). Even though
we are further from the Sun now than in mid-winter, the high position
above the celestial equator (and above the southern horizon) maximizes
the solar heating of the ground. Southern hemisphere folks are heading
At the beginning of the month, Saturn is still in the early evening
sky, setting about an hour after sunset. Mercury and Venus are above
Saturn, about 20 degrees off the western horizon, within a degree
of one another. Venus is very bright, and may be the first “star”
to emerge from twilight. Jupiter is about 45 degrees above the horizon
to the southwest. Mercury will disappear into the Sun’s glare
by the end of June, but Venus will remain in the early evening sky.
Jupiter will settle to about 30 degrees off the horizon by August.
Predawn planet watchers will find Mars which high above the southeast
horizon at sunrise. Saturn returns to the morning twilight at month’s
end, rising about ½ hour before sunrise.
At mid-month, an overhead view about 2 hours after sunset still
gives us a little more to cheer about than last month. Although
Hercules is not a constellation dominated by extremely bright stars,
use binoculars to find the spectacular globular cluster M 13 (13th
in the Messier catalog). You’ll have a better chance early
in the month, when there is less interference from the moon. This
sits at the edge of the faint luminous band of the Milky Way, which
stretches from the northeast to the southern horizon at this time,
curving gently toward the east.
From zenith to the southwest, you’ll find the bright star
Arcturus in the constellation Bootes, about half way to Jupiter.
To the south you can find the red star Antares, in Scorpio. Antares
means “rival of Mars” – a tribute to its red color,
though Mars is not visible in the evening sky this month. From Hercules
toward the eastern horizon you’ll find the bright blue star
Vega, in the constellation Lyra. With binoculars you may find the
faint Ring Nebula just south of Vega. Below Vega, the next bright
star you’ll notice is Deneb, marking the “tail”
of the swan in Cygnus. This constellation lies in the direction
towards which the Sun orbits in the plane of the Galaxy. It is also
the direction toward which the Voyager 1 probe is making its exit
of the solar system.
At the “head of the swan” we find the beautiful binary
Albireo. The imaginary line from Deneb to Albireo marks the approximate
plane of the Milky Way. If we follow that line to the south we’ll
note Altair, the brightest star in Aquila, and then the familiar
“tea pot” shape of Sagittarius, which marks the direction
toward the center of our Galaxy.
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.