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Tonight

Sun passes out of Leo and into Virgo on September 17

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Today – September 17, 2014 – the sun exits the constellation Leo and enters the constellation Virgo. The sun will remain in front of the constellation Virgo the Maiden until it enters the constellation Libra the Scales on October 31. So, when the equinox arrives on September 23, the sun will be in front of the constellation Virgo. And so it has been for thousands of years. But it won’t always be that way.

Year’s fastest sunsets happen around the equinoxes

Sunrise over the Red Sea by EarthSky Facebook friend Graham Telford

Photo by EarthSky Facebook friend Graham Telford

Does the sun set faster around the time of an equinox? Yes. The fastest sunsets (and sunrises) occur at or near the equinoxes. What’s more, the slowest sunsets (and sunrises) occur at or near the solstices. This is true whether you live in the Northern or Southern Hemispheres. And, by the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.

Andromeda galaxy is Milky Way’s next-door neighbor

The Andromeda Galaxy with two of its satellite galaxies, via Wikimedia Commons. Click here to expand.

Excluding the Large and Small Magellanic Clouds (which can’t be seen from northerly latitudes), the Andromeda galaxy – also known as M31 – is the brightest galaxy in all the heavens. It’s the most distant thing you can see with your unaided eye, at 2.3 million light-years. To the eye, it appears as a smudge of light larger than a full moon. Follow the links inside to learn more about the Andromeda galaxy.

Find the Lagoon and Trifid nebulae

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Take a dip in the Lagoon nebula (M8) and Trifid nebula (M20) on these September evenings, especially if you’re in a place where you can see the starlit band of the Milky Way. If you’re in the Northern Hemisphere, look in the south to southwest at nightfall and early evening to see the beautiful constellation Sagittarius just above the horizon. The famed Teapot asterism, part of Sagittarius, appears to be pouring tea from its spout towards the horizon. The Lagoon and Trifid nebulae are in this part of the sky.

Use Big Dipper to find Polaris, the North Star

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You can find the North Star, Polaris, using the two outermost stars in the bowl of the Big Dipper. On September evenings, look for the Big Dipper in the northwestern sky. Notice that a line from the two outermost stars in the bowl of the Big Dipper point to the North Star. The Big Dipper circles the North Star much like an hour hand circling the center of a clock.

Moon and Pleiades late night September 13 until dawn

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You can find the Pleiades star cluster – sometimes called the Seven Sisters – easily just by looking for it. No other pattern in the sky is so little and yet so clearly shaped like a dipper. Late at night on September 13, 2014, until dawn on September 14, you can see the waning gibbous moon near this star cluster. The bright reddish star nearby is called Aldebaran.

Look for Cassiopeia the Queen in northeast after sunset now

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Cassiopeia the Queen can be found in the northeast after sunset on September evenings. This constellation has the distinct shape of a W, or M, depending on the time of night you see it. The shape of this constellation makes Cassiopeia’s stars very noticeable.

How to see the Summer Triangle in September

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The Summer Triangle consists of three bright stars in three separate constellations. The stars are Vega in the constellation Lyra, Deneb in the constellation Cygnus, and Altair in the constellation Aquila. The Summer Triangle is prominent on summer evenings, but now, as autumn begins, we still have several months to watch this huge star pattern that looms from south to overhead in the autumn evening sky.

Look for daytime moon in west after sunrise next few mornings

Photo Credit: Dan Bush

Photo Credit: Dan Bush

The Northern Hemisphere’s full Harvest Moon has passed. Now the moon is in a waning gibbous phase, which means it rises in the east later and later each evening. Look east before going to bed tonight to catch the moon over the eastern horizon. Then look in the west after sunrise tomorrow, or in the next few mornings, to see the daytime moon over your western horizon.

Star of the week: Delta Cephei is a famous variable star

Like lights in a dark tunnel, stars in the distant universe become fainter as they are farther away. But, because they pulsate at a particular rate always correlated to their intrinsic brightnesses, Cepheid variable stars reveal their own true distances. Image via The Last Word on Nothing

At the southeast corner of the house-shaped constellation Cepheus the King, there is an intriguing variable star called Delta Cephei. With clocklike precison, this rather faint star doubles in brightness and fades again every 5.36 days. You can see it change over a period of days. The entire cycle is visible to the eye alone in a dark-enough sky. This star and others like it have secured a place as important standard candles for establishing the scale of the galaxy and universe.