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9 votes
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Significance of astronomical twilight

After the sun sets the sky remains light for a while. The significance is that observations during astronomical twilight may be impaired by the continuing glow of the sky. After astronomical twilight, ...
James K's user avatar
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4 votes

what degree in the sky does the sun change color?

Here's a partial answer: As mentioned in the comments, the transmission of the atmosphere depends quite a lot on local factors. But given a transmission $T_0(\lambda)$ at zenith, the transmission at ...
pela's user avatar
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3 votes
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Is the appearance of the twilight not constant in the interval before the sunrise?

The length of Astronomical twilight isn't constant, but the main reason is the tilt of the Earth, and not the orbital speed of the Earth. The change from day to night is a result of the Earth spinning....
James K's user avatar
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3 votes

Is astronomical twilight always seen when the sun is 18 degrees under the horizon?

These values are convenient definitions rather than descriptions of an observable condition. So astronomical twilight is defined to be when the sun is between 12 and 18 degrees below the horizon. ...
James K's user avatar
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3 votes

How close can Venus be to the sun in the sky and still be visible to the naked eye?

Around 15 degrees. Viewing Venus when it's near the Sun is difficult, for much the same reasons that it's difficult to view the Moon when it's a very thin crescent. You have to deal with the light of ...
PM 2Ring's user avatar
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2 votes
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Website to calculate sun elevation on a certain day?

You can get that data directly from JPL Horizons. That just gives you raw data in ASCII format, but if you know how to code it's not too hard to convert the Horizons data into a chart. Here's an ...
PM 2Ring's user avatar
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2 votes

Solar eclipse impact on twilight

I have three individual observations (unfortunately just remote) of the event, in which the extension of the solar eclipse can be observed in the twilight belt. The observations I've managed to make ...
Geographos's user avatar
2 votes

Is astronomical twilight always seen when the sun is 18 degrees under the horizon?

It’s the very definition of astronomical twilight. Civil twilight is when the sun is 6° below the horizon. Nautical twilight is at 12°. Astronomical twilight is at 18°. These are also defined by ...
Pierre Paquette's user avatar

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