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Our Friendly Skies

September 10, 2008|By ROD MARTIN and ANDY SMETZE, Tristate Astronomers

Visible evening planets



Jupiter is the brightest evening planet low in the south.

Mercury, Venus, and Mars are in the west during evening twilight.

Visible morning planets



Saturn rises before the Sun late in September.

Solar system



An interesting grouping of planets occurs this month.  The grouping will not be easy to see because it occurs during bright, evening twilight.  The planets are Mercury, Venus and Mars. The dimmest of the three planets is Mars at +1.7 magnitude.  At near zero magnitude, Mercury is about four times brighter, but Mercury is always hard to find because of its low altitude.  At -4 magnitude, Venus is about 40 times brighter than Mercury.  Normally Venus is very easy to see, but this month it sets within an hour of the Sun so it stays low in the west. The three planets are about 26 degrees from the Sun.  A fist held at arm's

length is about 10 degrees, so the planets are only about two and one half fists from the Sun.  Don't use a telescope to try to find them!

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On Sept. 11, Mercury reaches its greatest elongation from the Sun.  That day Venus is also one-third of a degree from Mars.  One-third of a degree is less than the width of the full moon.  Mercury is 3.5 degrees from Venus on

the next day, Sept. 12. The brightest evening plant is Jupiter. It is in the south less than one third up the sky. It is in the constellation Sagittarius. This is the constellation that the Sun crosses at the beginning of winter. The very low altitude of the constellation explains why winters are so cold.

Saturn reached conjunction with the Sun on Sept. 3 as it passed behind the Sun from our viewpoint.  It will not be visible until it re-enters the morning sky in late September.

If your sky is dark, Uranus may be visible through binoculars.  It reaches opposition and rises around sunset and is visible all night.  Use a starchart to find this distant planet.

By the way, with all the planet talk, the newest dwarf planet is Makemake.

See what information you can find about it!

Sun and moon



Fall is almost here, along with the lengthening nights and shortening days.

The autumnal equinox marks the time that the center of the Sun crosses the celestial equator and moves into the southern hemisphere.  That happens at 11:44 a.m. on Sept. 22.  If you were standing on the Earth's equator that day, the Sun would be directly overhead at local noon. Usually we think that on the equinox, there are 12 hours of daylight and 12 hours of nighttime.  That actually occurs three days later on Sept. 25.  There is a good reason for that.  The Sun is a disc in the sky about 0.5 degrees in diameter.  Sunset is when the last part of the Sun disappears below the horizon, so most of the Sun has already set.  Sunrise is when the first part of the Sun appears above the horizon.  At the equator, the Sun's location on the equinox, the sky rotates about one degree in four minutes, so it takes an extra minute for the center of the Sun to be on the horizon. 

On Sept. 30, the Sun rises at 7:06, sets at 6:54 for 11 hours and 48 minutes of daylight. 

Daylight will continue to shorten until the winter solstice in December.

The Sun enters the astronomic boundaries of Virgo from Leo on Sept. 16.

The moon reaches full on Sept. 15, last quarter on Sept. 22, and new on Sept. 29.

This month's full moon is called the "Harvest Moon" because it rises in the east just as the Sun sets in the west giving the illusion of extra light to be able to finish outside chores. 

It is the closest full moon to the equinox.

Brish Planetarium



Public programs resume on Oct. 7 with "Galaxies."  There will be no program on Oct. 14.  All sorts of deep space objects, particularly

galaxies, are highlighted in this program. Programs are held most Tuesday evenings at 7 when schools are in

session.  Admission costs $3 for adults, $2 for children and students, and senior citizens with a WCPS gold card are free.

The Tristate Astronomers meet the third Wednesday of each month at 7:30 p.m. in the planetarium.  For more information about the club, go to www.tristateastronomers.org on the Web.

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

The planetarium's Web site is http://www.wcboe.k12.md.us/content/d_i_planet.cfm and the phone number is 301-766-2892.

Stay up to date with public programs and take a tour of the night sky with "Skylights," the Brish Planetarium's monthly podcasts on antpod.com.

antpod.com and "Skylights" are made possible by Antietam Cable Television, The Herald-Mail Newspapers and the Washington County Public Schools Public Information Office.

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