I need to know the "time", in minutes in relation to sunset, that "night" or nighttime actually starts.

Question

I am looking for the time (in minutes) from when sunset BEGINS to the actual onset of "night". Also, when should I be able to fully see 3 to 5 stars?

Answer 1

Go to:
http://aa.usno.navy.mil/data/docs/RS_OneDay.html

This will give you sunrise and sunset, as well as civil twilight for any location. It might be a good starting point. This site is great for looking up sunrise and sunset and figuring length of the day.

Answer 2

zee prime's answer looks good.
However, given the nature of the question (particularly the part about seeing 3 to 5 stars), it sounds as if your instructor is trying to get you to go outside and determine the time periods in question.

I would think that sunset begins when the orb of the sun APPEARS to touch the horizon and begin sinking below it. But when does night begin? When the sun completely disappears? When the sky is darker than a certain shade of blue? When the sky is totally dark except for stars? I have no idea. So maybe you have to rely on an official definition for that part (and it may vary by latitude and time of year).

As far as seeing 3 to 5 stars, that will depend on your visual acuity, weather conditions, pollution conditions, light conditions (it's harder to see stars near a city), and also how quickly the sun sets (which depends on your latitude and the time of year). Also, do planets count for this purpose? On a good night, all or most of the first 3 to 5 stars could be planets. All of which is why I think your instructor wants you to report on your own experience looking for stars.

Answer 3

There are two concepts called civil twilight and astronomical twilight. Try googling them; I've forgotten the details. The further you are from the Equator, the longer twilight is, because at high latitudes the Sun sets at an oblique angle. In the tropics, when the Sun sets, it gets dark very quickly.

Answer 4

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Answer 5

it depends on your location. try putting your zip code or city into weather.com. it is usually listed somewhere in the forecast.
example
http://www.weather.com/weather/wxdetail/USNV0049?dayNum=1
lookin the blue "night box"