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Light levels on planet of Alpha Centauri-A at night?



 
 
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  #1  
Old January 17th 05, 11:33 PM
Phillip Gabero
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Default Light levels on planet of Alpha Centauri-A at night?

Hi group!

Let's say

- there was a habitable planet around Alpha Centauri-A
- at 1,2 AU
- A & B are at closest approach (11,2 AU)
- B is at opposition, getting the planet as close as
10 AU to B
- A is 90° below the horizon, B is 90° above the horizon

At 10 AU Alpha Centauri-B's apparent magnitude is -20,9,
which makes it 223 times dimmer than our sun.

My question now is what are the light levels like at that
time? I mean, we all know what light levels a full moon
produces, but what is "223 times dimmer than our sun" like?

I witnessed a partial eclipse back in 1999, when the moon
covered 99% of the sun where I live. With the sun at ~55°
above the horizon it was still pretty bright (clear skies).

Compared to that light levels on the planet around Alpha
Centauri A would still be 2 times dimmer (magnitude-light levels?),
but I guess this means "no night" during that time of the
year nevertheless.

What do you think (and feel free to correct any mistakes/wrong
assumptions)?
  #3  
Old January 19th 05, 11:00 PM
Aidan Karley
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Default

In article , Mr. 4X wrote:
time? I mean, we all know what light levels a full moon
produces, but what is "223 times dimmer than our sun" like?


Well, maybe like night in a modern city which has lots of street lights.

I heard a statistic recently that normal office lighting is around
1/500th of the brightness of midday sunshine. You could estimate the
difference by comparing the settings that an auto-exposure camera gives
you.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

 




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