Download The Night Sky

The Night Sky
August: The Month for Meteors
Every August, the night sky produces its own version of fireworks, the Perseid meteor shower.
This meteor shower is a summertime classic and among the oldest and most publicized of all
such showers. Astronomers have determined that comet Swift-Tuttle is the source of the Perseid
shower as once every year the Earth passes through the ancient dust trail left behind by the
passage of the comet around the Sun. Records of observation of the Perseid meteor shower go
back as far as two thousand years. The trail of dust is so old that it contains larger than average
particles, thus this shower is known for having exceptionally bright, colorful meteors leaving
long trails across the sky. The meteor shower takes its name from the constellation Perseus
which rises in the northeast around midnight during August. The meteors appear to originate in
the sky from the direction of this constellation so they are more likely to be seen after midnight.
The shower is easily observed by northern hemisphere viewers and this year the moon is setting
at mid-evening during the peak of the shower providing a dark sky for observing. The Perseids
can produce 50 to 100 meteors per hour under the best of conditions with an occasional fireball
also possible. The best viewing hours for this year’s Perseid meteors will probably be from
about 2 a.m. until dawn on August 11, 12 and 13. One only needs to find a dark, open sky far
away from the harsh glare of city lights to enjoy the shower. You don’t need to know the
constellations or any special equipment, just look up to watch the meteors streaking through the
nighttime sky.
Although the meteors will only be visible for a brief period, Venus remains the evening star in
the west while Saturn moves slowly westward during the month of August. Both planets are the
first starlike objects visible in the early evening twilight to the southwest with Venus near the
horizon and Saturn much higher and to the left of Venus. Jupiter will dominate in the pre-dawn
sky rising in the east-northeast with Mars positioned slightly below and to the left of Jupiter.
Mercury will be too close to the Sun to be visible this month. The full moon will fall on August
20th, well past the peak of the meteor shower.
In addition to a famous meteor shower, August is also the best month for viewing the Milky
Way. It is brightest and broadest when looking south toward the constellations Scorpius and
Sagittarius. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars
of which the sun is just one. The center of our galaxy lies some 30,000 light years away in the
direction of Sagittarius, but also above the stinger of Scorpius. Although impressive to the naked
eye, binoculars will reveal this region is rich in star clusters and nebulae (gas clouds).
The ETSU Powell Observatory open houses are on hiatus for the summer. They will resume in
September.
This month’s Night Sky was written by Dr. Gary Henson, Associate Professor in the Department
of Physics and Astronomy. He can be reached at [email protected]. Astronomy-related
information for the public, including a link to ETSU astronomy public outreach programs, can be
found at http://www.etsu.edu/cas/physics/outreach/astronomy.aspx.