The Sky this Week: September 13–September 22, 2013 Your daily digest of celestial events coming soon to a sky near you. By Richard Talcott — Published: September 13, 2013 Asteroid 324 Bamberga reaches opposition and peak visibility Friday, September 13. // Astronomy: Roen Kelly Friday, September 13 Asteroid 324 Bamberga reaches opposition and peak visibility today. The 140-mile-wide space rock lies in Pisces the Fish, just northwest of that constellation’s Circlet asterism. The asteroid glows at magnitude 8.1, which puts it within range of binoculars from a dark site. Although Bamberga was the 324th asteroid astronomers discovered, it is larger than half of the first 10 asteroids. It eluded detection for a long time because it follows a fairly eccentric orbit, which means it rarely gets close to Earth. In fact, it appears closer and glows brighter now than at any time in the past 22 years. Saturday, September 14 The Moon’s absence from the morning sky these next few days provides observers with a nice opportunity to see the zodiacal light. From the Northern Hemisphere, the time around the autumnal equinox is the best for viewing the elusive glow before sunrise. It appears slightly fainter than the Milky Way, so you’ll need a clear moonless sky and an observing site located far from the city. Look for a cone-shaped glow that points nearly straight up from the eastern horizon shortly before morning twilight begins (around 5 a.m. local daylight time at mid-northern latitudes). The Moon remains out of the morning sky until September 18, when the waxing gibbous returns and overwhelms the much fainter zodiacal light. If you miss the light this week, you’ll have another chance to see it during the first half of October. Sunday, September 15 The Moon reaches perigee, the closest point in its orbit around Earth, at 12:31 p.m. EDT. It then lies 228,286 miles (367,391 kilometers) away from us. Monday, September 16 The variable star Algol in Perseus reaches minimum brightness at 1:34 a.m. EDT. Observers on the East Coast who start watching around midevening can see the star’s brightness diminish by 70 percent over the course of about 5 hours. Those in western North America will see Algol brighten noticeably from late evening until dawn starts to paint the sky, when the star passes nearly overhead. This eclipsing binary system runs through a cycle from minimum (magnitude 3.4) to maximum (magnitude 2.1) and back every 2.87 days. September mornings should provide amateur astronomers with their first decent views of Comet ISON (C/2012 S1) as it makes its way into the inner solar system. // NASA/Hubble Tuesday, September 17 September mornings should provide amateur astronomers with their first decent views of Comet ISON (C/2012 S1) as it makes its way into the inner solar system. You’ll likely need a 10-inch or larger telescope to spot the comet, which currently glows at around 12th or 13th magnitude. ISON now stands in eastern Cancer about 2.5° northeast of magnitude 1.6 Mars, an area that is well clear of the horizon by 4 a.m. local daylight time. For more information about observing the comet, see “Get your first peek at Comet ISON” in the September issue of Astronomy. Wednesday, September 18 Full Moon occurs at 7:13 a.m. EDT tomorrow morning, but our satellite looks almost completely illuminated both tonight and Thursday night. This evening, you can find it rising in the east around sunset and peaking in the south shortly after midnight. The Moon lies among the dim background stars of Pisces, below the Great Square of Pegasus. As the Full Moon closest to the autumnal equinox, this is also the Harvest Moon. In early autumn, the Full Moon rises about half an hour later each night compared with a normal lag close to 50 minutes. The added early evening illumination supposedly helps farmers bringing in their crops. Saturn passes just 4° north of Venus on September 19. // Damian Peach Thursday, September 19 Look low in the west-southwest as darkness falls this week and Venus will grab your attention. The brilliant planet shines at magnitude –4.1, far brighter than any other point of light in the sky. If you target Venus through binoculars, however, you’ll see that it has a companion. Saturn passes just 4° north (to the upper right) of Venus this evening, but the two remain within the same binocular field all week. At magnitude 0.7, the ringed planet shines about 1 percent as bright as its neighbor. Friday, September 20 Although autumn arrives with the equinox in just 2 days, the Summer Triangle remains prominent in the evening sky. Look high in the west after darkness falls and your eyes will fall on the brilliant star Vega in the constellation Lyra the Harp. At magnitude 0.0, Vega is the brightest member of the Triangle. The second-brightest star, magnitude 0.8 Altair in Aquila the Eagle, lies some 35° southeast of Vega. The asterism’s dimmest member, magnitude 1.3 Deneb in Cygnus the Swan, stands about 25° east-northeast of Vega. For observers at midnorthern latitudes, Deneb passes through the zenith at approximately 9:30 p.m. local daylight time, about an hour after twilight ends. At the end of this week, Jupiter stands out among the background stars of Gemini the Twins from the time it rises until twilight is well underway. // Craig and Tammy Temple Saturday, September 21 Shining at magnitude –2.1, Jupiter stands out among the background stars of Gemini the Twins from the time it rises (shortly before 1 a.m. local daylight time) until twilight is well underway. This week, Jupiter lies about halfway to the zenith in the eastern sky at the start of morning twilight. A telescope shows Jupiter’s 37"-diameter disk and at least two parallel dark belts in its atmosphere. Sunday, September 22 With the days growing shorter and kids back in school, it shouldn’t be surprising that summer’s reign is just about over. The warmest season comes to an official close at 4:44 p.m. EDT, when Earth reaches the autumnal equinox. This marks the moment when the Sun crosses the celestial equator traveling south. Our star rises due east and sets due west today. If the Sun were a point of light and Earth had no atmosphere, everyone would get 12 hours of sunlight and 12 hours of darkness. But the air and finite size of our star make today a few minutes longer than 12 hours. From Astronomy - The Sky this Week - astronomy/
Posted on: Sun, 15 Sep 2013 09:13:03 +0000
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