Earthsky Tonight - Sep 20 2009

Will you catch the moon and Spica low in twilight after sunset?

Tonight is SEP 20, 2009

The new moon fell on Friday, September 18. That’s the time each month when the moon passes most nearly between the Earth and sun. It’s when the moon is traveling across the sky with the sun during the day.

When and where will you next see the moon? At each new moon, the moon passes from the morning to the evening sky. In the several days after new moon, a thin waxing crescent moon shows up in the west at dusk.

That could happen tonight. Will you see the young crescent moon and Spica, the brightest star in the constellation Virgo, low in the west after sunset tonight? Maybe. But maybe not.

The moon moves continually in orbit around Earth. As seen on our sky’s dome, the orbital motion of the moon carries our companion world farther from the sun-Earth line each day. And thus tonight’s moon is farther from the sunset than last night’s moon.

Still, autumn is nearly upon us in the northern hemisphere. That means you’ll have a hard time catching the young crescent moon and Spica after sunset tonight. Spica, the spring and summer star, fades in the twilight dusk at this time of year. And the ecliptic – or the path of the sun, moon and planets – makes a narrow angle with the horizon at sunset around the time of the autumn equinox. This fact keeps the waxing crescent moons in autumn low in the sky – and tougher than usual to see.

The whereabouts of the ecliptic in our sky is related to Earth’s orbit around the sun. (Are you getting an idea of cycles upon cycles in the celestial sphere? You should, because that’s the reality.) Earth’s tilt on its axis – which carries the sun low in winter and high in summer – also keeps the young crescent moon from being easily visible after sunset in the autumn months.

But the sky is nothing if not reliable. The moon will keep moving in orbit around the sun, and thus the crescent moon in our evening sky will keep moving farther from the sunset each night. You’ll see it one night soon, if you don’t see it tonight.

Written by Deborah Byrd

Comments (5)

at 05.49 am on 09-20-2009 Qudratullah

People of the NWFP could see the moon on Saturday evening and today on Sunday we observe Eid.Some people object to the sighting of the moon for being very small.But as to Earth Sky if the new moon happened on Friday then its sighting on Saturday is justifiable.Thanks

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at 06.18 am on 09-20-2009 Deborah Byrd

Yes, I believe it could be justifiable to say that the waxing crescent was seen on Saturday evening. That was a tough observation, though, for the reasons given in the post above. In springtime, it's easy to see a waxing crescent a day after new moon. In autumn, it's harder, because the ecliptic - the path traveled by the moon - makes a narrower angle with the horizon on autumn evenings. Still, given an extremely clear sky ... it might be possible.

at 06.24 am on 09-20-2009 Deborah Byrd

By the way, Qudratullah, here is a story about this event: http://www.nation.com.pk/pakistan-news-newspaper-daily-english-online/Politics/20-Sep-2009/Several-districts-celebrating-Eid-in-NWFP

I don't know if it's appropriate to congratulate you on this celebration (it comes once each month, does it not?), but if it is appropriate please accept my congratulations and best wishes.

Deborah

at 08.15 am on 09-23-2009 wermaro

Qudratullah, by all known criteria it was not possible to see moon on Sat. 19th Sep . in whole Pakistan, You people just claimed to to see the moon to deviate from rest of Pakistan. Shame on the people who give false witnessing againts scientific calculations. Why you can not keep the 30th day of fasting.
Be part of Pakistan and do not encourage private maulvis. please..... this will lead to Talibinization

at 6.12 pm on 09-20-2009 Ray H

last night saturday.. it was a ufo. this is what happened. My friend told me to check it out... this object in the sky. i thought it was a plane but this object stayed there for 20 seconds. after 20 seconds the smoke came out and the object went up and vanished. then the smoke kinda fade out..lasted about 14 seconds... the object its like a bright yellow... it wasnt what the nasa said.. god damn cover ups... i'm here in baltimore maryland.. the lunch was in Va they said.. just imagine.. a rocket doesnt stop in the middle of nowhere and people knows that. if the purpose of this rocket they say was to create smoke and come down? or vanished using, speed of light mark? damn Nasa should tell people the truth... if the worlds in danger, so be it, at lease people would know and get ready if something happen. rather then waiting for unexpected and have no option to get ready for something so big to come and knock us all out in one strike. It's basicly a cmon sense.

sincerely;
ray

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