Moon and Planets, April 2011

Look southeast in mid-April for the Moon, Saturn and Spica

Podcast above is from Abrams Planetarium.

April 2011 brings more daylight hours.  On April 1st, the sun is in the sky for about 12 hours, 45 minutes in the northern part of the United States.  By April 30, the daylight hours increase to 14 hours.

Saturn is the only bright planet that shines throughout the night this month.  The yellowish ringed planet rises in the eastern sky around sunset, is in the southern sky at midnight, and sets in the western sky near sunrise.    On April 2, Saturn is at oppostion; that is, it is opposite the sun in the sky.  At this time, our planet is directly betwen the sun and Saturn.  Saturn takes nearly 30 years to revolve around the sun, but because of its slower speed, Earth catches up to and passes Saturn every 378 days (1 year, 13 days).  In 2012, Saturn’s opposition is April 15.

On April 16, the moon appears near Saturn and Spica.  Use the moon as a guide at mid-month to locate those objects.  Saturn is distinctly yellow and the star Spica is blue in color.  The chart above shows the moon, Saturn and Spica on April 16 at 9 p.m.

In contrast, Venus and Mercury are never seen at midnight from the skies of Earth.  Both planets are between the earth and sun.  Because of this geometry, the two planets are seen near sun, either in the west after sunset or in the east before sunrise.  With Mercury being closer to the sun, it is rarely seen in a dark sky.  Unless the moon, bright planet or bright star is the vicinity, Mercury goes unnoticed.  In contrast, Venus is farther from the sun and can appear high in the east before sunrise or in the west after sunset.  Because of its brilliance, Venus has been called the “Morning Star” or “Evening Star.”  Generically, any bright planet can be given those names.

Mercury was visible in March in the evening sky.  By early April, its rapid revolution carries it between the sun and Earth (inferior conjunction) and into the morning sky.  During the past several weeks, brilliant Venus has moved farther from Earth, appearing low in the eastern predawn sky.  The manner in which we view the solar system during spring mornings places the planets low in the sky. 

Similarly, Jupiter was visible in the western sky at sunset during March.  From our view on Earth, Jupiter passes behind the sun (conjunction) early in April and moves into the morning sky.  Jupiter moves at about twice the speed of Saturn around the sun, yet Earth catches up and passes Jupiter every year and 34 days.  In contrast, Mars moves about half the speed of Earth and our planet catches it every 2 years, 50 days.

Look for a planetary grouping at the end of April, 2011.

In late April 2011, four planets are clustered near the horizon.  This occurs in bright twilight, so a binocular or telescope is necessary to locate these objects.  As shown in the diagram above on April 30 at 5:30 a.m., a crescent moon appears above bright Venus.  Dimmer Mercury appears to the lower left of Venus.  Both Mars and Jupiter appear just above the horizon.

As the calendar turns into May, Jupiter, Mars and Venus will make additional interesting planetary groups.  Be sure to check back in early May 2011 for that month’s update.

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