Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation w ritten by a professional astronomer.

2021 November 14
The illustration shows a decision tree showing how 
to identify bright lights that you might see in the 
night sky. 
Please see the explanation for more detailed information.

How to Identify that Light in the Sky
Illustration Credit & Copyright: HK (The League of Lost Causes)

Explanation: What is that light in the sky? Perhaps one of humanity's more common questions, an answer may result from a few quick observations. For example -- is it moving or blinking? If so, and if you live near a city, the answer is typically an airplane, since planes are so numerous and so few stars and satellites are bright enough to be seen over the din of artificial city lights. If not, and if you live far from a city, that bright light is likely a planet such as Venus or Mars -- the former of which is constrained to appear near the horizon just before dawn or after dusk. Sometimes the low apparent motion of a distant airplane near the horizon makes it hard to tell from a bright planet, but even this can usually be discerned by the plane's motion over a few minutes. Still unsure? The featured chart gives a sometimes-humorous but mostly-accurate assessment. Dedicated sky enthusiasts will likely note -- and are encouraged to provide -- polite corrections.

Chart translations: Spanish, Italian, Polish, Kannada, Latvian, Norwegian, and Turkish
Tomorrow's picture: volcanic light pillar


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