MAINE SKIES

A look at the Earth’s tilt in 2015

Posted Jan. 29, 2015, at 1 p.m.
Last modified Feb. 04, 2015, at 12:15 p.m.

This year the Earth was at perihelion or closest approach to the sun on Jan. 4, when the two were separated by a distance of about 77,450,000 miles. The Earth will be at aphelion or most distant from the sun on July 6 when they are separated by about 94,550,000 miles. In other words, we are more than 17 million miles closer to the sun in January than in July, so why is it colder in winter than summer? Distance has little to do with it. The answer lies with the fact that the Earth’s axis of spin lies 23.5 degrees from the perpendicular. Simply put: We are tilted 23.5 degrees away from the sun in the winter and a like number of degrees toward it in the summer. This tilt is also responsible for the seasons. The spring equinox on March 20 this year marks the sun’s transition across the celestial equator into the Northern Hemisphere and June 21 its most northern journey to 23.5 degrees above the equator. Its journey then begins towards the southern hemisphere with the fall equinox occurring on Sept. 23 and the sun reaching to 23.5 degrees below the equator on Dec. 22, the winter solstice. Without this tilt there would be no seasons. However the tilt does gradually change over time. Milutin Milankovitc (1879-1958), a Serb astronomer, theorized that changes in the Earth’s orbit and tilt over time are responsible for the Earth’s pattern of ice ages and warm periods such as the one we are now experiencing.

Focus on the Planets

Mercury is very low in the southeast about 45 minutes before dawn. Using binoculars look for the elusive inner planet to the lower left of the crescent moon on Feb.16.

Venus dazzles in the west an hour after sunset and, as the sky’s brightest point of light, cannot be mistaken for anything else.

Mars rises in the west after sunset where it keeps company with Venus and approaches its brilliant neighbor for a spectacular conjunction on Feb. 21.

Jupiter rises in the east at sunset and is up all night setting in the west at dawn. Jupiter’s belts and zones, along with their atmospheric cloud features, will be on display as well as its four major moons as they dance about and across the face of the giant planet.

Saturn rises by 4:00 a.m. in the south with the rings open at 25 degrees or nearly as far as they ever get affording views of the two ring systems and the Cassini Division separating them.

Uranus may be spotted as a faint blue-green dot just to the upper left of Venus or, on Feb. 21, only a degree to the moon’s crest.

Neptune lies just to the right of Venus but will likely be lost in the haze of sunset. Sky & Telescope Magazine’s finders chart at skypub.com/urnep will aid in locating these distant planets.

February events

1 Sunrise, 6:55 a.m.; sunset, 4:43 p.m.

2 Candlemas or Groundhog Day. A cross-quarter day marking the midpoint between the winter solstice and spring equinox.

3 Full moon, 6:09 p.m. The full moon of February is the Snow Moon or Hunger Moon. Look for Jupiter just to the left of the moon this evening.

6 The moon is at apogee or farthest distance from Earth today.

7 Venus sparkles on the west-southwest horizon an hour after sunset with much fainter Mars just to the upper left.

12 Moon in last quarter, 10:50 p.m.

13 Golden Saturn is just to the right of the moon tonight with Antares below them to complete a tight triangle.

16 The sun enters Aquarius on the ecliptic.

18 New moon, 6:47 p.m. The sun enters the astrological sign of Pisces but astronomically has just entered Aquarius.

21 All eyes should be on the western horizon tonight where Mars and Venus are separated by less than a degree with the crescent moon just above. Uranus is a tiny blue-green light directly below the moon.

25 First-quarter moon, 12:14 p.m. Aldebaran, the red eye of the Bull, is to the lower right of the moon.

28 Sunrise, 6:15 a.m.; sunset, 5:22 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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