December 18, 2017
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Understanding the Earth’s rotation

By Clair Wood , Special to the BDN

The Earth rotates on its axis at an angle of 23.5 degrees from the perpendicular. As it points towards the stars, it also undergoes a “wobble” similar to a spinning top that traces out a circle when viewed from above. Known as precession, it is the source of many celestial events. One is the fact that astronomical and astrological “houses” are not the same. The path of the Earth around the sun is called the zodiac and is divided into 12 “houses” or constellations. It takes about 25,800 years for precession to sweep out a complete circle or about 2150 years to move from one house to the next. Astronomers take this movement into account where astrology does not. This leads to anomalies such as in this month when the sun enters the astrological sign of Sagittarius on the 22nd and the astronomical sign of Scorpius on the 23rd. Next month other events governed by precession will be covered.

Focus on the planets

Mercury may be visible during the first few days of November very low in the east-southeast about a half-hour before sunrise. It will soon disappear for most of the month.

Venus rises in the pre-dawn eastern sky early in the month in Virgo in company with its dimmer and smaller companion Mars.

Mars accompanies Venus into the pre-dawn southeastern skies. On Nov. 7, check out the compact triangle formed by Venus, Mars, and the crescent moon high in the southeast about an hour before sunrise.

Jupiter is the first of the trio of planets to appear in the east rising at about 2:00 a.m. as the month opens and midnight by month’s end.

Saturn, the only major planet in the evening sky, opens the month very low in the southwest and will be lost to view by mid-month.

Uranus is a blue-green disk among the stars of Pisces high on the southwestern horizon before midnight.

Neptune is high in south as the evening twilight vanishes. The finder’s chart published in the September issue of Sky & Telescope (p.48) or at skypub.com/urnep will aid in finding the two far distant and elusive planets.

November events

1 First Sunday in November means we are to set our clocks back one hour to Standard Time. Sunrise, 6:13 a.m.; sunset, 4:24 p.m.

3 Moon in last quarter, 7:25 a.m.

7 Moon at apogee or farthest distance from Earth. Remember to check the southeast an hour before sunrise where Venus, Mars and the moon form a tight triangle.

11 New moon, 12:47 p.m.

14 Looking to the east-southeast at about 5:00 a.m. will reveal Venus, Mars and Jupiter in an ascending line from left to right.

18 Peak night for the Leonid meteor shower that has produced huge meteor storms in the past, the last being in 2002. This year, watchers can expect about 15 meteors per hour coming from the Sickle of Leo with some interference from the crescent moon. Some sightings can be fireballs that rival Venus in brightness.

19 Moon in first quarter, 1:28 a.m.

22 The sun enters the astrological sign of Sagittarius.

23 The sun enters Scorpius on the ecliptic. The moon is at perigee or nearest approach to Earth.

25 Full moon, 5:44 p.m. The full moon of November is called the Beaver Moon, Hunter’s Moon or Frosty Moon.

30 The sun enters Ophiuchus on the ecliptic. Sunrise, 6:51 a.m.; sunset, 3:57 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.

 


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