Download July 2013 - Joliet Junior College

JULY 2013 ASTRONOMY
From the Trackman Planetarium at Joliet Junior College
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On July 5th, Earth will be at its farthest from the sun for the year - 94.5 million
miles. In January, we are 91.4 million miles from the sun. Because we are farther
from the sun in July, we move a little slower in our orbit - about 2,200 miles per
hour slower than in January. Now that we are past the summer solstice, the days
are getting shorter. We lose 42 minutes of sunlight during July.
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Venus dominates the western sky after sunset. Venus is the third brightest object
in the sky after the sun and the moon. Venus is bright because it is covered in
white clouds of sulfuric acid and carbon dioxide which reflect 70 percent of the
sunlight striking the planet. That cloud cover also gives Venus a runaway
greenhouse atmosphere - atmosphere where the sun’s heat can penetrate to the
planet’s surface but can’t escape. This makes Venus the hottest planet in our
solar system with surface temperatures approaching 900 degrees. If you look at
Venus with binoculars, you will see that it has phases like our moon. That is
because Venus is between Earth and the sun. Venus will be in the evening sky
through the rest of the year.
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Saturn is low in the sky in mid-evening. Follow the curve of the handle on the
Big Dipper, past the bright star Arcturus, and Saturn will look like a yellow star
below Arcturus and to the left of another bright star -Spica. On July 16th the
moon will be close below Saturn. Mercury, Jupiter and Mars all rise before the
sun and are in the early morning sky. On July 22nd, Jupiter will be within one
degree of Mars. The pair will rise at 3:45 am. Earth will be at its closest approach
to Pluto for the year on July 1st. The one-time planet, now known as a “dwarf
planet” or “Plutoid”, will be 2.9 billion miles from Earth. You will need a fairly
good sized telescope to find it. We have a spacecraft (New Horizons) on its way
to Pluto and it will arrive in the vicinity of the planet in July of 2015.
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The Big Dipper is high and slightly to the west in the evening sky. Its handle is
pointing down toward the horizon and to Arcturus which is in the constellation
of Bootes. Below Bootes is Virgo, the constellation where Saturn is currently
located. The three stars of the Summer Triangle are now in the eastern sky in
mid-evening. They are Vega in Lyra, Deneb in Cygnus, and Altair in Aquila.
The Milky Way runs between those three stars and is a good area to scan with
binoculars. The center of the galaxy is in the constellation Sagittarius, a
constellation that looks like a teapot and is low on the horizon. To the right (east)
of Sagittarius is Scorpio and it looks like a scorpion with two claws.
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The full moon in July is on July 22nd. This moon was called the Full Thunder
moon by the Native Americans. If you missed the “super moon” in June, look
for the full moon in July. July’s full moon is 99% the size of June’s “super” full
moon.
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The new moon is at 2:15 am on July 9th CDT. The day after the first sighting of
the crescent moon after the new moon is the first day of Ramadan, the greatest
religious observance in Islam. Ramadan is observed with 30 days of fasting and
prayer. Since the moon moves about 13 degrees across the sky every 24 hours,
the first date that the crescent moon can be seen will vary from country to
country. For the United States and 62 other countries, Ramadan begins on July
9th this year according to the Makkah Calendar. For 132 other countries,
Ramadan begins on the 10th.
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The Delta Aquarids meteor shower is on the 29th. Look to the southeast after 11
pm. There will be a 61% (gibbous) moon that night so viewing will not be
optimal.
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Factoid: The Earth is 7,926 miles wide. (From North Pole to South Pole it is 25
miles shorter which makes the Earth a geoid rather than a spheroid.) Water
covers about 71 percent of the Earth’s surface, but if you took all of the water on
Earth and formed it into a ball, the ball would only be 860 miles wide. The
volume of fresh water available to humans would be a sphere about 35 miles
wide. (All fresh water on Earth is not accessible to us. There is more fresh water
under the surface - ground water - than there is above the surface.) Source: U.S.
Geological Survey
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There is a Chinese spacecraft crossing the skies during July. The easily seen
spacecraft is Tiangong -1. (Tiangong translates to “heavenly palace.) Tiangong 1 is frequently manned by Chinese astronauts called taikonauts though the
schedule is not publicized in advance. Look for Tiangong in the southsoutheastern sky, halfway between the horizon and the zenith at 9:15 pm on July
15th or almost directly overhead on July 16th at 9:40 pm.
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Art Maurer
Director -Trackman Planetarium
Joliet Junior College
([email protected])