- John Zimmerman
- Posted On
Lake County Skies: The autumnal equinox
LAKE COUNTY, Calif. – Sept. 22 marks the official end of summer. This is when the autumnal equinox occurs.
What’s an “equinox”?
An equinox is when the sun is directly over the Earth’s equator. Due to the tilt of the Earth on its axis, normally the sun shines to the north or south of the equator.
But twice a year, on March 20 (vernal equinox) and Sept. 22 (autumnal equinox), it is directly over the equator.
The effect of an equinox is for the days and nights to be the same length. Indeed, the word equinox is derived from the Latin words “aequus” meaning equal, and “nox” meaning night.
Directly overhead during September night skies is the Summer Triangle. This is a pattern of three bright stars, Vega, Deneb and Altair. Use our star chart to identify them.
Vega is the fifth brightest star in the sky, Altair the 12th, and Deneb the 19th. All three are relatively young stars which means they burn hotter than older stars, like our Sun.
Surprisingly, the term “Summer Triangle” did not originate until the 1900s.
Our star chart shows the “planet” Pluto to the south. We use the word planet in quotes because Pluto lost its planet status in 2006.
First discovered in 1930, Pluto was the ninth and smallest of the planets.
As our astronomical technology improved, we began discovering other objects similar in size to Pluto which were called minor planets.
As the number of these grew, maintaining Pluto’s planet status no longer made sense.
In July 2015 the “New Horizons” space probe will pass near Pluto giving us images and data nevr before seen.
You cannot see Pluto with the naked eye. If you have a telescope, Pluto is not a very rewarding object.
At magnitude 13.65, you would need at least a 6-inch scope, and with that Pluto would only resemble a tiny gray star.
As a point of interest, the name “Pluto” was adopted from a suggestion by an 11-year-old schoolgirl from England.
John Zimmerman is a resident of Lake County and has been an amateur astronomer for over 50 years. For more information about astronomy and local resources, visit his Web site at www.lakecountyskies.com .