March 30, 2018


Night Sky:
Venus, Arcturus, Spica and Other Highlights of the Night Skies for April

By Gerry Lebing

Start April by looking across the sound to the west, right around sundown.  If the skies are clear, you will easily spot Venus, the third brightest object in our skies - (only the sun and the moon are brighter!)

Venus is named after the Roman god of love and beauty.  It’s often called the evening star.  Venus is the second planet from the sun and roughly the same size as earth. 

But Venus is not earth’s twin. Earth has a climate that supports a wide variety of life.  This is largely due to our atmosphere, which is composed of 78% nitrogen, 20% oxygen and 2% trace gases, including 0.033% CO2.  Venus’s atmosphere is mostly composed of carbon dioxide (CO2).  This thick layer of CO2 traps the infrared radiation from the sun, making Venus the hottest planet in the solar system.  The surface temperature of Venus is close to 900 degrees Fahrenheit!  It’s hard to imagine life existing under such harsh conditions.

Once you get done admiring Venus, there are two stars rising on the other side of the celestial sphere that are two stars worth noting.

Arcturus, the brightest star in the Northern Celestial Hemisphere, (but only the fourth brightest in the night skies), will rise in the east at 7:36 p.m. Arcturus is a red giant. It has about 1.5 times the mass of the sun, but its diameter is 25 times bigger than the sun’s. The size and color of Arcturus indicate it is an old, cool star, (7250 degrees Fahrenheit; 7.5 billion years old), that burns helium for fuel. Arcturus is about 37 light years away.

The name Arcturus means “Bear Watcher.”  The Greeks probably gave it this name because of its proximity to Ursa Major (the Big Dipper) and Ursa Minor (the Little Dipper.)

About 45 minutes later, another bright star, Spica, will rise south of Arcturus.  Spica is the 15th brightest star in the night skies, with a magnitude of +1. It is about 250 light years away. It has 10 times the mass of the sun and 7 times the radius. Spica is a blue-white giant star and believed to be one of the hottest stars visible. Its surface temperature is about 22,500 degrees!

Spica is much younger then Arcturus.  The name is derived from the Latin phrase “spica virginis,” which means “Virgo’s ear of grain.” Spica is a binary star but it is very hard to see – it is much smaller than its companion star. Keep an eye on Spica as scientists think it has the potential to become a super-nova sometime in the next few million years!

If you happen to have access to a telescope, you might want to look a little bit above and to the North of Arcturus. With any luck you might see M94.

 

M94 is 16 million light years away.  It was discovered by Pierre Mechain in 1781.  Two days later, Charles Messier added it to his list. M94 has an inner blue ring surrounded by a red ring.  The inner ring is believed to be a starburst area characterized by intense star formation.  Don’t let the reddish hue of the outer ring lead you to believe it is only populated with older stars (like Arcturus.)  Scientists believe up to 10% of the galaxy’s new star formation is taking place in this outer ring. If you look closely, there are traces of blue in and around the red ring.  These are probably areas of star production!

Other things you can look for April 2018.

Jupiter, Mars, and Saturn will follow each other across the night skies starting around 10:30 p.m. on the night of April 1.  Mars and Saturn will rise “together” at about 2:06 a.m. on the morning of April 2. 

The Lyrids Meteor Shower will peak on the night of April 22.  You can expect to see about 20 meteors per hour scattered throughout the sky.  Best viewing will be after midnight!

Moon Phases:
1st Full Moon is April 29
Last Quarter is April 8
New Moon is the April 15
1st Quarter is the April 22

(Gerry Lebing is a retired computer scientist with the U.S. Geological Survey in Washington, D.C.  He has visited Hatteras Island since the mid-1970s. He and his wife, Karen, have owned property here for several years and moved to their home in Waves full-time in 2013.  Astronomy is a subject that Gerry says he has always been interested in and one that he pursues seriously -- he's built an small observatory next to his house. You can send him questions about the night sky through e-mail, [email protected]g.)





comments powered by Disqus