The sky this week for October 17 to 21

The sky this week for October 17 to 21

Longer nights bring familiar constellations, autumn meteors, and your last chance to see our solar system’s largest planet this year.
Wednesday, October 17

The waxing gibbous Moon crosses into Capricornus this evening, where it has a magnificent encounter with magnitude –0.9 Mars. Once twilight fades away, the pretty pair stands some 30° above the southern horizon with Mars 6° to the Moon’s left. The two edge closer as the evening progresses. Unfortunately, North American observers won’t see their actual conjunction, which occurs at 9 a.m. EDT tomorrow when our satellite passes 2° due north of the planet. By the time darkness falls tomorrow evening, a slightly fatter Moon appears 6° to Mars’ left. A telescope shows several subtle surface features on the Red Planet’s 13″-diameter disk.

The Moon reaches apogee, the farthest point in its orbit around Earth, at 3:16 p.m. EDT. It then lies 251,175 miles (404,227 kilometers) from Earth’s center.

Wednesday, October 17

The waxing gibbous Moon crosses into Capricornus this evening, where it has a magnificent encounter with magnitude –0.9 Mars. Once twilight fades away, the pretty pair stands some 30° above the southern horizon with Mars 6° to the Moon’s left. The two edge closer as the evening progresses. Unfortunately, North American observers won’t see their actual conjunction, which occurs at 9 a.m. EDT tomorrow when our satellite passes 2° due north of the planet. By the time darkness falls tomorrow evening, a slightly fatter Moon appears 6° to Mars’ left. A telescope shows several subtle surface features on the Red Planet’s 13″-diameter disk.

The Moon reaches apogee, the farthest point in its orbit around Earth, at 3:16 p.m. EDT. It then lies 251,175 miles (404,227 kilometers) from Earth’s center.

Thursday, October 18

The days of viewing Jupiter in the evening sky are quickly running out. The giant planet now lies low in the southwest during twilight, hanging barely 10° above the horizon 30 minutes after sunset. Still, Jupiter shines brightly at magnitude –1.8 and should stand out if you have a clear and unobstructed horizon. The low altitude means a telescope won’t show much detail in the planet’s cloud tops.

Friday, October 19

Although autumn began a few weeks ago and the stars of winter’s Orion now rule the morning sky, the Summer Triangle remains prominent on October evenings. 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 mid-northern latitudes, Deneb passes through the zenith around 8 p.m. local daylight time, just as the last vestiges of twilight disappear.

Saturday, October 20

The variable star Algol in Perseus reaches minimum brightness around 10:39 p.m. EDT, when it shines at magnitude 3.4. If you start tracking it this evening, you can watch it more than triple in brightness (to magnitude 2.1) by dawn. This eclipsing binary star runs through a cycle from minimum to maximum and back every 2.87 days. Algol remains visible all night, passing nearly overhead around 2 a.m. local daylight time.

Sunday, October 21

If you’re up early this morning, you should see a number of bright streaks peppering the sky. These are Orionid meteors, which belong to an annual shower that peaks before dawn. The waxing gibbous Moon sets around 4 a.m. local daylight time, leaving nearly two hours of dark skies for observers. At its peak, the shower should produce up to 20 meteors per hour radiating from the northern part of the constellation Orion the Hunter.

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