Our Friendly Skies - September 2009

August 31, 2009|By ROD MARTIN / Brish Planetarium and ANDY SMETZER / Tristate Astronomers

Visible evening planets

Jupiter is visible all night.

Visible morning planets

Venus is very bright in the east before sunrise.

Jupiter is visible all night.

Mars is high in the southeast.

For more information about the visible evening planets and nighttime sky, download the Washington County Planetarium's podcast "Skylights" from

Solar system

Jupiter dominates the evening sky this month. It is easy to spot its disc and four bright satellites with a good pair of binoculars if you hold them very steady. Jupiter is the brightest evening night object at -2.8 magnitude except the moon.

The four bright satellites were discovered by Galileo 400 years ago. At that time, many believed that everything revolved around Earth. His discovery and observations of Jupiter's satellites helped prove observationally that not everything orbited our planet. This helped prove the sun-centered ideas of Copernicus.


In his honor, these satellites are called the Galilean moons of Jupiter. To celebrate the discovery, 2009 has been designated as the International Year of Astronomy.

Go out and look at this brilliant planet. It is fun to follow the various motions of the moons. They look like four stars near Jupiter. They change their positions from hour to hour and it's easy to see the changes from night to night.

An unusual event occurs on Sept. 3 after midnight (the night of Sept. 2). The moons will appear to disappear. Europa and Callilsto will be directly in front of Jupiter and Io and Ganymede will pass behind. This alignment will not happen again until 2019.

Neptune is east or left of Jupiter. The two have been partners for a couple months, but both are still close enough to see. Neptune is tough to see at +7.8 magnitude. You will need a small telescope or good binoculars to see its grayish disc.

Obscure Uranus reaches opposition on Sept. 17 in Pisces near the Aquarius border. Slightly brighter than magnitude +6, it is near but usually just beyond naked eye visibility. Opposition is when it is directly opposite the sun in our sky and is visible all night.

Saturn is dipping rapidly toward the western horizon, setting with the sun most of the month. It reaches conjunction on Sept. 17 and will be entering the morning sky. Don't count on seeing Saturn this month. That is unfortunate, since on Sept. 3 the rings are edge-on to Earth for the first time since 1996.

Mars is climbing higher in the morning sky as it moves through Gemini. It is slightly brighter than +1 magnitude, but is not as bright as most of the nearby stars. Its color helps reveal it.

Venus is the brightest morning planet slightly below -4 magnitude. It is now dropping toward the sun, but is actually becoming easy to see very well since geometry makes it stand at a higher angle.

Mercury reaches inferior conjunction on Sept. 20 when it passes between Earth and the sun. It may be visible low in the west during early September, but is not visible most of the month.

Sun and moon

On Sept. 1, the sun rises at 6:39 a.m. and sets at 7:42 p.m., for 13 hours and 3 minutes of daylight. By Sept. 30, the sun rises at 7:06 a.m. and sets at 6:55 p.m., for 11 hours and 49 minutes of daylight.

The sun enters the astronomical boundaries of Virgo from Leo on Sept. 16.

The moon reaches full on Sept. 4, last quarter on Sept. 11, new on Sept. 18, and first quarter on Sept. 26.

Brish Planetarium and events

Public planetarium programs will resume Oct. 6 with "Planets." This program talks about the objects of our solar system as well as planets around other stars. The programs will be held Tuesdays at 7 p.m. Admission is $3 for adults, $2 for children and students, and senior citizens with a WCPS Gold Card are admitted free.

The planetarium is at the Central Offices of Washington County Public Schools on Commonwealth Avenue off Frederick Street in Hagerstown.

For more information, go to For more information about schedules and special events, go to

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