Why can we see only one side of the moon? The answer is gravity. We are all familiar with the effect of the moon’s gravity on the Earth’s ocean tides, but the Earth has an even greater gravitational effect on the moon. “Tidal locking” creates a braking effect on the moon’s rate of spin as it orbits the Earth resulting in the rate of spin being equal to the time of orbit, about 27.3 days, so the same side always faces us. This is known as a synchronous rotation. The “near” side of the moon that we see is relatively smooth with large volcanic plains. The “far” side, or “dark” side as it is sometimes called, is rougher, craggy and dotted with impact craters with one being among the largest craters in the solar system. The far side of the moon was first seen by the Soviet Luna 3 probe that sent back pictures in 1959. It was directly seen by humans aboard the Apollo 8 spacecraft in 1968. Dark side is a misnomer since the far side receives as much sunlight as the near side. Also about 9 percent of the far side can be seen from Earth because of the elliptical nature of the lunar orbit.
Focus on the planets
Mercury is low in the east-northeast about an hour before sunrise as June draws to a close. Orange Aldebaran lies just to Mercury’s upper right.
Venus shines brilliantly well up in the west as darkness deepens. It cannot be mistaken for any other heavenly body.
Mars lies on the far side of the sun from Earth during June and is lost to view for the month.
Jupiter opens the month high to the upper left of Venus and is much dimmer than its sister planet. As the month progresses, the two draw closer together culminating in their being within two-thirds of the moon’s width of each other on the last day of June.
Saturn is visible in the southeast at nightfall and remains in view all night. Saturn’s rings are tilted for optimum viewing and its major moon Titan is easily spotted by telescope.
Uranus and Neptune are in the east-southeast before dawn. The blue-green disk of Uranus and the blue-gray disk of Neptune can be spotted by powerful binoculars and with the aid of Sky & Telescope magazine’s finder’s chart at skypub.com/urnep.
June events
1 Sunrise, 4:53 a.m.; sunset, 8:14 p.m. Venus blazes high in the west an hour after sunset with Jupiter well to its upper left. The two stars directly to the right of Venus are Castor and Pollux.
2 Full moon,12:19 p.m. The full moon of June is the Strawberry Moon and also is known as the Flower Moon or Rose Moon. Orange Antares stands to the right of the moon with Saturn to the lunar upper right.
9 Last quarter moon, 11:42 a.m.
10 The moon is at perigee or nearest approach to Earth today.
16 New moon, 10:05 a.m.
20 The moon, Jupiter and Venus form a close triangle in the west an hour after sunset with Regulus just to the upper left.
21 Summer solstice, 12:38 p.m. The sun enters the astrological sign of Cancer at the solstice. The is the point of the sun’s greatest advance into the northern hemisphere and will now begin its journey toward the celestial equator.
22 Astronomically the sun enters Gemini on the ecliptic but astrologically has just entered Cancer.
23 St. John’s Eve when midsummer in England was celebrated by great bonfires across the land. Moon at apogee or farthest distance from Earth today.
24 The June Bootid meteor shower goes over the next several days. A normally weak display did have a rate of 20 plus per hour in 2004. Look for a rate of up to five per hour of slow-moving meteors. Moon in first quarter, 7:03 a.m.
28 Mercury is low in the eastern pre-dawn sky with Aldebaran to its upper right. An hour after sunset Saturn is nestled to the lower right of the moon.
30 Jupiter and Venus are extremely close together in the west an hour after sunset. Sunrise, 4;52 a.m.; sunset, 8:25 p.m.
Send astronomical queries to Clair Wood at cgmewood@aol.com or care of the Bangor Daily News, Features Desk, P.O. Box 1329, Bangor, ME 04402.