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Our Friendly Skies

July 03, 2007

By ROD MARTIN / Planetarium Resource Teacher

and ANDY SMETZER / Tristate Astronomers

Visible Evening Planets

VENUS is bright in the west, but loses altitude by month's end.

SATURN is low in the west.

JUPITER is in the east at sunset.

Visible Morning Planets

MARS is in the east.

JUPITER is in the west at sunrise.

MERCURY appears low in the east late in July.

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Venus is by far the brightest planet at magnitude -4.4. Geometry makes Venus appear brightest on July 12. Since Venus is closer to the sun than to Earth, the planet never seems to stray too far from the Sun in the sky. Around mid-month, Venus will begin its dive into the evening twilight until it disappears in early August.

Saturn is in the southwest in front of the nose of Leo the Lion. Saturn is fairly bright at magnitude +0.6. The ringed planet has a close encounter with the moon on July 16. That night, the crescent moon moves within one-tenth of a degree of Saturn. That is about one-fifth the width of the moon.

Jupiter is in the southeastern sky after evening twilight and is visible within the stars near the summer Milky Way. It is easy to spot at magnitude -2.5. Only one bright star is nearby, Antares in Scorpius. Use binoculars or a small telescope to see its four larger satellites.

Mercury entered the morning sky last month and has its best morning display of 2007 this month. Look about a half hour before sunrise for the bright star. Even though it is at greatest elongation on July 20, the twilight makes it a challenging object to spot.

Mars is becoming brighter and higher in the morning sky. Brightening to +0.6 magnitude, the red planet rises around 2 a.m. early in July, and just after midnight late in the month as it passes from the constellation Aries into Taurus.

Sun and moon

The summer solstice was last month, so this month you should notice that the sun begins to rise later in the morning and set earlier in the evening. This trend will continue until the winter solstice in December.

The orbit of Earth, and all planets, is elliptical. That means that there is a point in the orbit that Earth is closest to the sun called perihelion, and a point most distant from the sun called aphelion. Seasons are a result of Earth's tilt, not the distance from the sun. Earth is actually slightly more than 3,100,000 miles closer to the sun in January than in July. Aphelion in 2007 occurs on July 6, when Earth is about 94,500,000 miles from the sun.

The midpoint of 2007 was at noon on July 2.

On July 1, the sun rose at 5:47 a.m. and set at 8:43 p.m., for daylight of 14 hours and 56 minutes. By July 31, the sun rises at 6:09 a.m. and sets at 8:25 p.m., and has daylight of 14 hours and 16 minutes. The sun enters the constellation Cancer on July 21 from Gemini.

This month, the moon is at last quarter is on July 7, the new moon is on July 14, first quarter is on July 22, and the full moon on July 29.

Brish Planetarium/Tristate Astronomers

Public planetarium programs have concluded for the current school year. They will resume in the fall with the Hubble Telescope Program, which was one of the most popular ones presented by the planetarium. The schedule will be released later in the summer.

Go to antpod.com to download or listen to "Skylights," the planetarium podcast. Provided by Antietam Cable and The Herald-Mail, monthly sky tours hosted by Rod Martin of the Brish Planetarium can be downloaded to help you find your way across the night sky.

For more information about the planetarium and Tristate Astronomers, visit their Web sites through www.tristateastronomers.org and navigate to the planetarium's page. To contact the planetarium, send e-mails to martirod@wcboe.k12.md.us.

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