Aug 06

What’s Up in the Sky

Good Timing for Perseids

Everyone’s favorite summer meteor shower, the Perseids, has a good chance of fulfilling our expectations this year and its peak should occur at a convenient time.  This year the shower should be best on the Saturday night/Sunday morning of August 11/12.  With luck you may be able to observe one to two meteors per minute on average after midnight.  And that rate should increase as the night progresses until dawn.

Meteor showers occur when Earth collides with a swarm of particles left in the path of a comet that orbits the Sun.  It’s sort of like driving through a snowstorm or encountering a swarm of insects on a bike ride.

As the comet passes close to the Sun, solar radiation causes gases and solid particles to be released from the surface of the comet nucleus.  These particles follow the comet’s orbit and when Earth’s orbit intersects their path, we plow through the swarm and the particles burn up in our atmosphere.  More specifically, friction between the particle and the air ionizes the nitrogen and oxygen molecules that make up most of the atmosphere, causing the gases to glow and thereby leaving a visible trail which we observe.

The best way to observe a meteor shower is to find a site with a clear view of the horizon and away from the glow of city lights.  Set up a lawn chair, have a blanket or sleeping bag handy in case the night is chilly, bring some insect repellent just in case, and look up.  No special equipment is necessary – this is a naked eye observation.

August offers several other opportunities for interesting observations.  If you look low in the west-southwest an hour after sunset, you should see three relatively bright objects in a triangular formation.  These are Saturn on top, the star Spica on the bottom, and Mars in between.  Watch each night as Mars drifts toward the south, passing right between the others on August 13 and 14.  On the evening of the 21st, the trio is joined by a thin crescent Moon, a rare, beautiful gathering.

For you early risers, the planet Venus dominates the predawn sky.  Look for it just below the waning crescent Moon an hour before sunrise on the 13th.  Later that afternoon the Moon will pass in front of (occult) Venus.  This will be a chance for serious observers to witness a rare event, although a small telescope will be needed.  For more information see the August issue of Sky and Telescope magazine.

All in all, this should be a good month to enjoy what’s up in the sky.


This month in history:

August 5:                Neil Armstrong born – 1930

August 11:              Deimos, moon of Mars, discovered by Asaph Hall – 1877

August 1:                Saturn V production ends – 1968

August 18:              Cassini spacecraft flies by Earth – 1999

August 20:              First Redstone rocket launched – 1953

August 25:              Voyager 2 flies past Saturn – 1981

August 30:              NASA approves Lunar Orbiter program – 1963