October 23, 2017
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Big Whack theory may explain moon’s origin

By Clair Wood, Special to the BDN
Missing Credit
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The current accepted theory for how the Earth gained its moon is the so-called Big Whack theory put forward by William Hartmann in 1975.

This scenario has the Earth being struck by a large body gouging out a piece of the crust that eventually formed the moon. The moon should, as a result, bear isotopic signatures from both the Earth and the colliding body.

Recently, Junjun Zhang of the University of Chicago made mass spectroscopic studies of the lunar samples brought back by the 1970s Apollo missions. She found that the titanium-50 to Ti -47 ratios were essentially identical to those of the Earth’s. Samples from meteorites, the closest stand-in to the colliding body available, are quite distinct from those of Earth.

Several explanations are being put forward to reconcile Zhang’s findings with the Big Whack theory and Zhang herself says, “Our study cannot provide a definite answer to the moon’s origin,” however she adds, “it does place a new constraint to the Earth-moon evolution system.” The research was published in the March 26, 2012 issue of Nature Geoscience.

Focus on the planets

Aug. 13 finds Venus in the northeast with the crescent moon nearby to the upper right. Farther to the upper right is Jupiter with Aldebaran directly to its right and finally the Pleiades well above Jupiter.

Mercury lies just above the eastern horizon about an hour before sunrise at midmonth, where it is just to the lower left of a thin crescent moon on Aug. 15. Mercury sinks into the morning twilight by month’s end.

Venus rises in the east all month and dominates the early morning sky. Venus is visited by the crescent moon on Aug. 13.

Mars may be found well up on the southwest horizon after sunset in the company of Saturn and Spica. On Aug. 13, the trio form a nearly straight line.

Jupiter rises in the east-northeast around 2 a.m. as the month begins and by midnight as it ends. Aug. 11 finds Jupiter, the moon and Aldebaran forming a triangle with Venus to their lower left.

Saturn is in the west at nightfall where, on the evening of Aug. 21, it forms a lopsided square with the moon, Mars, and Spica. Saturn’s moons, other than Titan, will be difficult to spot, however, the ring system is tilted 14 degrees to our line of sight, offering an excellent view.

Uranus is high in the southwest among the stars of Cetus during the very early morning hours.

Neptune occupies the constellation of Aquarius during the midnight hours. Sky & Telescope magazine will publish finder’s charts for both Uranus and Neptune in next month’s issue and online at skypub.com/urnep.

August events

1: Sunrise, 5:21 a.m.; sunset, 8:02 p.m. Lammas, a cross-quarter day marking the midpoint between the summer solstice and fall equinox.

2: Full moon, 11:26 p.m. The full moon of August is called the Sturgeon Moon, the Green Corn Moon and the Dog Day’s Moon. Aldebaran is close to the lower right of Jupiter at dawn.

9: Moon in last quarter, 2:56 p.m. The moon is at apogee, or farthest distance from the Earth, today while the sun enters Leo on the ecliptic.

10: Mars, Saturn and Spica form a close circle on the western horizon an hour after sunset.

12: This is the peak night for the Perseid meteor shower with the moon being little more than a nuisance factor. The best time for viewing will be after midnight and estimates are given for between 20 and 100 sightings per hour. Perseids are fast, bright and often leave persistent trails.

13: Venus is just to the lower left of the moon with Jupiter to the upper right around 3 a.m. on the eastern horizon.

15: Mercury is to the lower left of the moon in the early dawn looking like a fairly bright star.

17: New moon, 11:53 a.m.

22: The sun enters the astrological sign of Virgo but astronomically is still in Leo.

23: Moon at perigee or closest approach to Earth.

24: Moon in first quarter, 9:54 a.m.

31: Full moon, 9:57 a.m. This is the second full moon for August, making it a Blue Moon. Sunrise, 5:56 a.m.; sunset, 7:15 p.m.

Send astronomical queries to Clair Wood at cgmewood@aol.com or c/o Bangor Daily News Style Desk, P.O. Box 1329, Bangor 04402.

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