EYES TO THE SKY September 5 – 17, 2017

Full Corn Moon, Sirius the Dog Star harbinger of autumn

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A nearly full moon rises in the east-southeast this evening at 7:15pm, synchronized with sunset at 7:22pm on the opposite horizon. The Full Corn Moon reaches full phase about 8 hours later, at 3:04am on the 6th. That makes for viewing on the 5th the closest to full.

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PHOTO: Astrophotographer Craig Boynton’s solar eclipse

For those of us who, 2 weeks ago, witnessed the total solar eclipse in faraway locations, and those of us who observed the partial eclipse locally, this full moon is especially charged. Then, our eyes were riveted on the dark moon, new moon, orbiting between Earth and Sun, the sun’s light at the moon’s back. In the coming days we receive the reflected light of the sun streaming from a fully lit moon that is positioned opposite the sun with Earth in-between – the position of the moon at full phase. Contrast the photograph of full moon with the image of new moon eclipsing the sun. We are pleased to publish amateur astrophotographer Craig Boynton’s solar eclipse photograph. He explains, “There was a slight cloud cover at my Missouri location; I think that was the cause of the magenta color in the corona.”

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While absorbed in writing about preparations for the solar eclipse, I postponed celebrating the heliacal* rising of Sirius the Dog Star that occurred around August 17. At that time the beautiful harbinger of autumn star had just emerged from the sun’s glare and still posed a challenge for pre-dawn stargazers with obstructed views to the southeast horizon. By now, Sirius is 20 degrees above that horizon and may be spotted along with brilliant planet Venus shining in the east: look for Sirius to the right of Venus until about 5:50am on the 6th and 6:00am on the 17th. Sunrise is at is at 6:23 today and on the 17th, 6:35.

Follow the moon in the coming weeks as it wanes to a crescent in the early morning sky. Familiar constellations of winter nights rise in the darkness and are still visible about an hour before sunrise. On the 17th and 18th, looking east, the crescent moon guides us to a 3-planet line-up. Timing is crucial if we are to see the planets: Mercury rises at 5:14 on the 17th and 5:17 on the 18th. It could be 30 minutes later over an obstructed or polluted skyline. Bring binoculars.

*Heliacal risings occur after a star has been behind the Sun for a season and it is just returning to visibility. There is one morning, just before dawn, when the star suddenly reappears after its absence. On that day it “blinks” on for a moment just before the sunrise and just before it is then obliterated by the Sun’s presence. That one special morning is called the star’s heliacal rising. Each day that passes after the heliacal rising, the star will appear to rise earlier and remain in the sky longer (that is, not blink) before its soft glow is obliterated by the rising sun. From http://solar-center.stanford.edu/AO/dawn-rising.html

This map shows the sky (as seen when facing east) on July 15, 3000 BC from the ancient city of Memphis, Egypt. Sirius stands 3 degrees high 32 minutes before sunrise around the time of its heliacal rising. Stellarium via SkyandTelescope.com

This map shows the sky (as seen when facing east) on July 15, 3000 BC from the ancient city of Memphis, Egypt. Sirius stands 3 degrees high 32 minutes before sunrise around the time of its heliacal rising. Stellarium via SkyandTelescope.com

Resources
http://www.skyandtelescope.com/observing/a-real-scorcher-sirius-at-heliacal-rising/
http://solar-center.stanford.edu/AO/Sirius.mov
http://solar-center.stanford.edu/AO/dawn-rising.html

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