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JULY 2013 ASTRONOMY From the Trackman Planetarium at Joliet Junior College ¶ 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. ¶ 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. ¶ 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. ¶ 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. ¶ 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. ¶ 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. ¶ 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. ¶ 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 ¶ 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. ¶ Art Maurer Director -Trackman Planetarium Joliet Junior College ([email protected])