Cumberland Times-News

Bob Doyle - Astronomy

September 21, 2013

Bright points highlight night sky in the west

Last week’s column was about the Big Dipper, the most popular star figure to Americans.

Today’s column is about two bright points in the west, one seen at dusk (as early as 7:45 p.m.) and the other seen later in the evening.

As it begins to get dark, you will notice a lonely point of light in the west (same direction where the sun earlier set). You will notice that this point shines steadily, in contrast to the twinkling stars.

As it get dark, this point drops lower and becomes brilliant, putting to shame the night stars. You are seeing Venus, our nearest planetary neighbor.

Venus is five times brighter than Jupiter, the next brightest planet. Venus’ intense light is due to its closeness both to the sun and the Earth and the highly reflective clouds that shroud Venus’ surface.

  Venus visibility has a cycle lasting 584 days. Last March, Venus was on the far side of its orbit from us and invisible in the sun’s glare.

As Venus travels around its orbit, its average speed is 20 per cent faster than our Earth’s speed. So very slowly, Venus has increased its visibility and is now over 43 degrees from the sun.

 Venus is now setting about 100 minutes after sunset. Venus’ low height is due to her appearing in Libra, a zodiac group that never gets high above the horizon in our area.

Slightly below and to the right of Venus is the planet Saturn. Saturn is much farther from the sun and Earth than Venus, so it appears only 1/80th as bright as Venus. You may need binoculars to be sure of spotting Saturn.

  Venus will be more striking in November, when it sets two and half hours after sunset.

In December, Venus will appear lower as it’s angle to the sun begins to drop. Our neighbor will then be in front of Sagittarius, the most southerly zodiac group.

  By the time Venus is about to disappear this week, you will notice a bright, twinkling star in the west. This is Arcturus (ark-TOUR-ess), a star that has been visible in the evening sky since spring.

Arcturus can be found by extending the Big Dipper’s handle to the left. In about one dipper’s length, you’ll see this orange-tinted star.

Arcturus is 36 light years away from Earth. So we see Arcturus as it was 36 years ago, in 1977.

Arcturus is a giant star, nearing the end of its life. (When stars run low on their central hydrogen, they being to fuse hydrogen further out, causing them to expand. Their surface temperature also drops.)

Arcturus is about 1,000 Celsius degrees cooler than our sun and shines most strongly in red and orange light.

Billions of years from now, our sun will become a giant star and incinerate its inner planets, including our Earth.

SKY SIGHTS AHEAD: The moon is now rising late in the evening; by Sept. 26, the moon will be rising after midnight. So early evenings may be a good time to spot the Milky Way from a place far from streetlights and shopping areas.

The gentle glow of the Milky Way runs from the northeastern horizon to directly overhead and then down to the southwestern horizon.

The bright star Vega, nearly overhead is part of the Summer Triangle, a trio of bright stars.

Facing South, the Milky Way covers most of the Summer Triangle.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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