Skylights featured twice on Earth Science Picture of
the Day: 1
Photo of the Week.. The whole sky appears in a drop
of water from a thawing winter icicle. This photo was featured on
Earth Science Picture of the Day for December 31, 2002.
Astronomy news for the week starting Friday, January 3,
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.