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First quarter Moon

Photo of the Week. A climbing first quarter Moon graces the daylight sky.

Astronomy news for the two weeks starting Friday, October 9, 2015.

The next skylights will appear October 23, 2015.

We begin our much quieter fortnight (as compared to the last period) with the Moon in its waning crescent phase as it heads toward new Moon on Monday, October 12. The morning of Saturday the 10th the slimming Moon will present a pretty sight in eastern twilight below Jupiter, with Mars and Venus above it. The following morning, that of Sunday the 11th, finds a very thin crescent just to the south of Mercury, the pairing hard to see in brightening dawn. The Moon will actually occult the planet as seen from far southern South America. Following new, we flip to the other side of the sky to watch the waxing crescent in the west. Your first view will be of an ultra-slim crescent the evening of Tuesday the 13th in fading dusk. The night of Thursday the 15th finds our satellite to the northwest of Saturn, while by the following night the crescent will have moved to the other side of the ringed planet. The phase ends at first quarter on Tuesday the 20th, after which our companion is seen in its waxing gibbous phase. On Sunday the 11th, the Moon passes apogee, when it is farthest from Earth and angularly smallest, by just over 5 percent less than average.

If you want to see a fine planetary lineup, get up early to watch the show. As the fortnight opens, we see Venus, Mars, Jupiter, and Mercury all in a ragged row descending toward the eastern horizon with Venus to the south of the star Regulus in Leo. They all then slowly shift position, Jupiter and Mars climbing toward much brighter Venus, Jupiter next in brilliance, Mars relatively faint, Mercury pretty low. At the same time, Jupiter gains on Mars, the giant planet passing just south of Mars the morning of Saturday the 17th, the whole configuration making planetary movement easy to follow. Way down at the bottom, Mercury passes greatest western elongation relative to the Sun on Thursday the 15th, rising just at the break of dawn. In the evening, Saturn sets early in the southwest, just after the end of twilight. Finally, Uranus is in opposition to the Sun on Sunday the 11th deep within the confines of Pisces as it heads towards Taurus and then Gemini, where it was found by William Herschel in 1781. With a mass 14.5 times that of Earth and a radius 4.0 Earth's, it's very different from Jupiter and Saturn. Visible to the naked eye, it was seen many times before formal discovery, but was taken for a star.

One of the better meteor showers of the year, the Orionids (which seem to come out of Orion), the product of Halley's Comet (which also produces May's Eta Aquarid shower), is active during much of October and early November. The Orionids peak the night of Wednesday the 21st and into the following morning, when with the Moon out of the way they can produce up to 25 meteors per hour. Mixed in with them are the much weaker Southern Taurid meteors (the product of short-period Comet Encke), which are active during October and into November. Toward the end of our period, the Northern Taurids (both emanating from the constellation Taurus) pick up as well.

Having passed the Autumnal Equinox in Virgo, the Sun is now headed toward Sagittarius and the Winter Solstice, whereupon winter begins in the northern hemisphere. To the northeast of Sagittarius find Capricornus, a faint figure that looks like an upside-down old cocked hat, but actually represents an improbable water goat. Now low in the south in the evening, the constellation is known for two naked-eye doubles, one that isn't (Algedi, the Alpha star) and one that is (Dabih, the Beta star) as well as a classic globular cluster (Messier 30). Proceeding farther to the northeast along the ecliptic and Zodiac we run headlong into Aquarius, the Water Bearer and then to complete the Zodiac's "Wet Quarter" Pisces (the Fishes), to which we can add Pisces Austrinus, the Southern Fish south of Aquarius, which comes with the bright star Fomalhaut, from Arabic the "Fish's Mouth."
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