Skylights featured on Astronomy Picture of the Day

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Skylights featured three times on Earth Science Picture of the Day: 1 , 2 , 3 , 4 .

Cloud waves

Photo of the Week.. Even overcast skies can be beautiful, as attested to by dramatic rolling waves of clouds, whose appearance depends on direction of view.

Astronomy news for the week starting Friday, January 2, 2004.

As we start the New Year, best wishes to all for 2004. This Skylights covers a two-week period. The normal weekly schedule will resume on Friday, January 16.

The Moon begins the fortnight in its waxing gibbous phase, brightening the sky and reaching full on Wednesday, January 7, after which the waning gibbous phase takes over until third quarter passage the night of Wednesday, the 14th, the latter taking place close to Moonrise in North America.

As it travels through the constellations of the zodiac, the near- full Moon will take on the giant planets. The night of Tuesday, the 6th, it will make a nice pass to the north of Saturn, which is now well up in Gemini in the northeast after the end of twilight. The Moon then repeats the event with Jupiter in Leo the morning of Monday, the 12th, Jupiter now rising in the east around 10 PM. As the Earth prepares to pass between Jupiter and the Sun early next March, this largest of planets begins its retrograde, westerly (against the stars) motion on Sunday, the 4th.

While Jupiter and Saturn dominate late-night skies, the inner planets are lords of twilight. You can easily admire Venus in southwestern skies at dusk, the planet now setting about an hour after the skies have fully darkened. 2004 is Venus's year, as it will transit across the Sun next June 8, an event not seen since 1882. While much more difficult to see, you might watch for Mercury low above the eastern horizon in dawn's light as the little planet approaches its greatest western elongation with the Sun on Saturday the 17th. In between, Mars still hangs out to the southwest, setting now around midnight.

Planets aside, one of the fine features of the fortnight is the excellent Quadrantid meteor shower, which peaks the morning of Sunday, the 4th, originates from a defunct constellation near the Big Dipper, and can produce the order of 100 meteors per minute.

While the year may belong to Venus, the first week of January belongs to sister Earth. On Saturday the 4th, at noon central time, with the Sun highest in the sky, our planet will pass perihelion with the Sun (where the two are closest) at a distance of 147.1 million kilometers (91.4 million miles), 1.7 percent closer than the average distance of 149.6 million kilometers (93.0 million miles). That we are closest to the Sun in the dead of northern winter clearly shows that the solar distance has nothing to do with the seasons, which are caused entirely by the tilt of the Earth's axis relative to the perpendicular to its orbit. That perihelion is close to the time of Winter Solstice passage is entirely coincidental.

Though spring is usually considered to be "Galaxy Time," when the dust of the obscuring Milky Way is out of the way, the early evening of fall and early winter are fine times to note the two closest large galaxies to Earth, M 31 in Andromeda, which is nicely visible to the naked eye, and M 33 in Triangulum, which lies between Mothallah (Alpha Trianguli) and Mirach (Beta Andromedae), but requires excellent eyesight and a very dark sky, the two roughly two million light years away. Later in the evening, winter skies are dominated by the beauty of the bright winter stars that feature Orion, Taurus, Auriga, Gemini, and Canis Major, the latter holding the brightest star of the sky, Sirius.
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