Skylights featured on Astronomy Picture of the Day

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Skylights featured twice on Earth Science Picture of the Day: 1 , 2


Photo of the Week.. The whole sky appears in a drop of water from a thawing winter icicle. This photo was featured on the Earth Science Picture of the Day for December 31, 2002.

Astronomy news for the week starting Friday, January 3, 2003.

Good wishes for the coming year.

We begin 2003 with one of those curious weeks with no quarterings of the lunar phase. The 29.53 day phase cycle divided by 4 will just fit into a seven day week with a bit left over at each end. New Moon was passed on Thursday, January 2nd, while first quarter will not be reached until Friday the 10th. As a result, we can spend the entire week watching the Moon in its waxing crescent phase, beautifully displaying Earthlight on its nighttime side. Under perfect conditions, you might be able to see the very slim crescent the night of Friday the 3rd very low in the west southwest in bright twilight. By the next night, the crescent will be obvious as it moves against the relatively faint stars of Capricornus. Since the Sun has just passed the Winter Solstice, the first quarter will be somewhat past the Vernal Equinox in Pisces. Since the Moon will be moving through Capricornus, on Saturday the 4th it will pass well south of Uranus and the next day to the south of Neptune, non-events really since the sky will be so bright you could not see them anyway.

Saturday, January 4th is much more important for an event that involves the Earth. Or it might be Thursday the 3rd, depending on where you live. Very close to midnight Eastern Standard Time, the Earth passes orbital perihelion, where it is closest to the Sun, a distance of 147.1 million kilometers (91.4 million miles), 0.983 times closer than the average of 149.7 million kilometers, which defines that basic distance measure in astronomy, the Astronomical Unit (AU). As a result of this slight proximity, the Earth now moves a bit faster in orbit than it does at aphelion (which will take place this year the night of July 3), causing the Sun to move faster between the Winter Solstice and the Vernal Equinox than it does between the Summer Solstice and the Autumnal Equinox. Northern hemisphere winter is therefore four days shorter than northern hemisphere summer (called the "inequality of the seasons," known since ancient times). Since perihelion passage occurs at midnight the 3rd, it will take place on the 4th to the east of North America's Eastern Time zone, and on the 3rd to the west of it. Since perihelion takes place in the cold of northern winter, the distance between the Earth and Sun clearly has nothing to do with the seasons (but everything to do with the 23.4 degree tilt of the axis). That perihelion takes place near Winter Solstice passage is purely a coincidence.

Be sure to admire Saturn, high in the northern-hemisphere sky around 10:30 PM, and Jupiter, which rises brilliantly around 7:30 PM, and then Venus, which is glorious in the morning hours to the east before dawn. If you are up in the morning, you might also get to see some meteors from the Quadrantid shower, perhaps one a minute or even more. The shower, which usually peaks on the morning of January 4, is named after the defunct constellation Quadrans (the Quadrant), which is near the handle of the Big Dipper.

This is the season for fine early evening viewing of the constellations of the Perseus myth. Look for the hero himself, as for those in mid-northern latitudes he flies on his winged horse nearly overhead around 8 PM, recognizable by fine streams of stars, the "W" of Cassiopeia a bit off to the west.
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