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The Night Sky Mars and the Moon Put on a Show The planet Mars is at opposition (i.e., opposite to the sun on the sky) on April 8th. Nearly a week later on the night of April 14th, Mars is closest to the earth for 2014. At opposition, a planet rises at sunset and sets the next morning at sunrise. Of the four inner planets of the solar system, the so-called “terrestrial (earth-like) planets,” Mars has the most eccentric orbit (i.e., flattened ellipse). This is the reason why the closest approach day is not on opposition day. Since Mars was at aphelion (i.e., the farther distance from the sun in its orbit) on January 1, 2014, this closest approach is not as close as Mars can get to us in its 1.9 year orbital period, but it is 4.9 million miles closer to us than the 2012 closest approach. Mars will be even closer to us, and brighter, at the 2016 and 2018 oppositions. All of this month, Mars is as bright as the brightest star in the night-time sky, Sirius. A few hours after sunset, compare the brightness of Sirius in the south-western sky to that of reddish Mars in the south-eastern sky. Note that the bright star just to the south-east of Mars is Spica in the constellation of Virgo. Jupiter continues to dazzle in the evening sky just to the south of Gemini’s brightest stars, Castor and Pollux. Jupiter is significantly brighter than Mars and is at eastern quadrature (90 degrees east of the sun) on April 1st. Jupiter is very near the northern-most point on the ecliptic (the earth’s orbital plane projected onto the sky), so it remains very high in the sky in the evenings for the remainder of the month of April. A half-lit moon shines near Jupiter during the evening of April 6th. April also gives rise to the evening reappearance of the Arcturus, the 4th brightest star in the night sky, located in the constellation of Boötes. Arcturus is one of my favorite stars since its reappearance in the evening sky is a sign that spring has returned. It is red giant star with a diameter 27 times that of the sun. One can easily find Arcturus by following the curve of the Big Dipper’s handle which can be remembered with the astronomy limerick, “Follow the arc to Arcturus.” If one continues this path in the sky, one can then find Spica – “then drive a spike to Spica.” The ringed planet Saturn rises at 10:30 p.m. EDT at the start of April and at 8:30 p.m. (in bright twilight) as April ends. Saturn will be at opposition on May 10th of this year. The rings of Saturn are tilted 22 degrees from edge-on which adds to Saturn’s brightness – Saturn rivals the brightness of Arcturus this month. On the morning of April 17th, a waning gibbous moon shines very close to Saturn. Brilliant Venus rises a little before the start of morning twilight low in the southeast. A waning crescent moon will appear just above and slightly to the right of Venus on the morning of April 25th – it should be quite a beautiful view! The moon is full on the night of April 14-15. This full moon is directly opposite of the sun, resulting in a lunar eclipse on this night. Unfortunately, one will have to stay up much of the night in order to see it. You will start to notice the moon’s brightness darkening around 1:30 a.m. The moon will enter the earth’s umbral shadow (darkest part of the shadow) at 1:58 a.m. starting a partial lunar eclipse. The moon will be completely inside the earth’s umbra at 3:07 a.m. starting the total eclipse of the moon. Mid-eclipse occurs at 3:46 a.m. – at mid-eclipse, the moon often has a reddish appearance as all sunsets on the earth shine on the moon’s surface. The moon will leave the earth’s umbra at 4:25 a.m. ending the total lunar eclipse. Following this, the moon will appear partially eclipsed until 5:33 a.m. as morning twilight begins. Note that the sun will rise at 6:55 a.m. on April 15th. The next free public astronomy open house at the ETSU Powell Observatory will occur on April 5th from 8:00 to 10:00 p.m. This marks the last astronomy open house until the fall. At these open houses, the public can view objects in the sky through telescopes and hear talks by faculty of the Physics and Astronomy Department. Note that the open houses are cancelled if the sky is cloudy. Further information about these open houses can be found on the web at http://www.etsu.edu/cas/physics/observatory/default.aspx. This month’s Night Sky was written by Dr. Donald G. Luttermoser, Chair of the Department of Physics and Astronomy. He can be reached at [email protected] Astronomy-related information for the public, including a link to the ETSU Powell Observatory, can be found at http://www.etsu.edu/cas/physics/outreach/astronomy.aspx.