Our Friendly Skies - September 2010

September 01, 2010|By ROD MARTIN / Brish Planetarium and ANDY SMETZER / Tristate Astronomers
  • All-Sky Chart for September 2010
Tristate Astronomers,

Visible evening planets

VENUS is bright low in the west after sunset.

MARS is low in the west.

JUPITER is visible all night, in the east after sunset.

Visible morning planets

JUPITER is visible all night, in the west before sunrise.

MERCURY is in the east in late September.

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

Solar system

The bright grouping of planets that we enjoyed all summer is starting to leave our sky over the next couple of months. There are two very bright planets, in fact, they are brighter than anything at night except the moon, for us to enjoy.

The brightest planet in the west is Venus. It is -4.7 magnitude, which is almost 10 times brighter than the next brightest planet. Take time to look at Venus through a small telescope or binoculars. You will notice that it is actually a thin crescent shape. The phases of Venus helped prove that it revolved around the Sun, not the Earth. Late in the month, Venus will set less than an hour after the sun.


In the opposite direction is the -2.9 magnitude Jupiter. It reaches opposition on Sept. 21. That is the time that it is directly opposite the sun in the sky and is closest to the Earth. It is visible all night and will dominate the sky when Venus leaves. Look for it below the square pattern of stars called Pegasus. Actually you can find the square after you see Jupiter. Your binoculars may show up to four of Jupiter's large satellites.

Even though Uranus is normally very difficult to find, this is the month to search! All month it is less than one degree north of Jupiter. That is about the width of two full moons. At +5.7 magnitude, you will definitely need a telescope or good binoculars. It is visible all night, too.

Mars has been hanging around the sky but becoming fainter and fainter as the Earth speeds away in its faster orbit. It is +1.5 magnitude and just resembles a dim red star near Venus. It is low in Virgo and will pass into Libra later this month.

Saturn was part of the trio of planets, along with Venus and Mars. Since their orbits are faster, Saturn has been left behind and enters the muck of the twilight this month. When it reappears in a month or so, it will be a morning planet.

Mercury will have its best morning appearance of the year during late September. Mercury passes between Earth and the sun on Sept. 3, then rapidly moves away. The geometry is perfect to give Mercury the steep angle to the horizon to be easy to spot during the last half of the month. Look at the spot the sun rises about a half hour before sunrise. The "star" is Mercury.

Sun and moon

Since the end of March we have enjoyed more daytime than nighttime. Unfortunately that is about to change. As Earth revolves around the Sun, sometimes we are leaning toward the sun to give us summer and part of the time we are leaning away from the sun to give us winter. The position of Earth when it is halfway between the two extremes is the fall equinox. That is the day that the sun seems to cross the celestial equator heading south. Daytime and nighttime are the same length and is an equinox, which means equal night.

This year's fall equinox occurs on Sept. 22 at 11:09 p.m. From that date until the vernal equinox in March, we will have more nighttime than daytime.

On Sept. 1, the sun rose at 6:38 a.m. and sets at 7:42 p.m. for 13 hours and 4 minutes of daylight. By Sept. 30, the sun rises at 7:06 a.m. and sets at 6:54 p.m., for 11 hours and 48 minutes of daylight.

The sun enters the astronomical boundaries of Virgo the Maiden from Leo the Lion on Sept. 16. Virgo is the largest zodiacal constellation and the sun spends more time within its boundaries than any other constellation.

The moon reaches last quarter on Sept. 1, new on Sept. 8, first quarter on Sept. 15, full on Sept. 23, and another last quarter on Sept. 30.

Brish Planetarium

Public planetarium programs will resume in October with the "Universe of Dr. Einstein." learn about the events that shaped the life of one of the greatest scientists ever. the program describes many of his theories and their impact on us.

The programs will begin the first Tuesday of October at 7 p.m. Admission fees are $3 for adults, $2 for students, and senior citizens with a WCPS Gold Card are admitted free!

The planetarium is located at the Central Offices of the Washington County Public Schools on Commonwealth Avenue off Frederick Street in Hagerstown. The planetarium's website is For more information about schedules and special events, go to

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