Skywatching July 2012


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Our planet reaches its farthest point from the sun on July 4, about 152 million km from the sun.

Moon Phases

Full — July 3
Last — July 10
New — July 18
First — July 26

The Morning Sky

Venus and Jupiter dominate the predawn eastern skies throughout the month.  (See our Venus posting about Earth’s nearest planet’s visibility for the remainder of the year.)

On July 1 at 4:20 a.m. Venus and Jupiter are near Aldebaran, the brightest star in Taurus. (When a planet is in front of a constellation, we say the “planet is in” that constellation, although the stars are much farther away than the planets. The stars form a distant backdrop of the planets’ celestial motions.)

By July 9, Venus appears near Alebaran at 4:20 a.m.

By mid-month the waning crescent moon enters the grouping with an interesting grouping of the two planets, the star and our celestial satellite.  Notice how Venus’ orbital motion carries it past Aldebaran during the first half of the month.

By month’s end Venus orbital motion carries it away from Aldebaran.  Jupiter’s orbital motion is not as evident and it generally follows the annual motion of the stars.  That is they appear in the east just before sunrise.  As the months progress they appear farther to the west each morning at the same time.  Several months later, they appear in the east at sunset and continue to appear farther in the west each evening at the same time until they disappear in the sun’s glare only to reappear later in the morning sky just before sunrise.

Watch this celestial motion during the July in the morning sky.

The Evening Sky

Mercury makes a brief appearance in the western sky, just after sunset.  It appears low in the western sky during early July.  With binoculars and clear horizon look for it near the horizon slightly north of west about 40 minutes after the sun sets.

Mars and Saturn are low in the southwestern sky just after sunset.  Saturn appears near the star Spica, the brightest star in Virgo.

At 9:45 p.m. on July 1, look for Saturn and Spica. They are nearly the same brightness, although Saturn has a yellow appearance and Spica has a blue tint.  Mars appears farther to the right.

Each night Mars’ orbital motion carries it farther to the east as compared to the westward motion of the stars as described above. During the second half of the month, the moon enters the region of Saturn and Mars. On the evenings of July 24 and July 25, the moon moves past the grouping.

By month’s end, Mars appears closer to Saturn and Spica than it did at the month’s start.

The image above shows the position of the planets on July 15, 2012 (Click the image to see it larger)  Mercury, Mars, and Saturn appear on the evening side of the sky from Earth.  Venus and Jupiter appear on the morning side of the sky from Earth.

July provides excellent examples of the planets’ motions.  Take a look to watch Venus rapidly move in front of the distant stars and in the evening watch Mars move closer to Saturn.