Expert: Jayendra Upadhye - 3/2/2006

Question
I was recently on holiday in the Indian Ocean, just north of the equator. Although the night skies were cloudless and there was little light pollution I was surprised to see that very few stars were visible to the naked eye. In contrast the night sky over England (where I live) is full of stars. Can you explain this?


Answer
Hi Kevin,
To tell you frankly i am not sure myself, there could be any amount of reasons. like say..
1 - The orion is a very prominent constellation which would have been visible to you on the equator. Associated bright stars betelguese, bellatrix, aldebaran, pleades, sirius, capella should have been visible. But a lot depends on time of observation. You see in summer (northern), these constellations are directly overhead (slightly to the north when one is on the equator), at around 9 to 10:30 pm
These are in the later hours followed by the big dipper, etc, and if i am not mistaken, towards the morning, by arcturus the red giant in scorpio.
To your south the hydra stars should have been visible.
(But my knowledge here is strictly sketchy, i am NOT a professional astronomer nor connected to planetarium work as some on this site are).

2 - Often when one is in tourist resorts, one finds starless skies not because there are no stars, but because there IS light pollution from powerful sources of light like neons no matter how few and no matter if they are relatively far away.(though you may not see a neon many blocks away, its light does blot out "slighly fainter" minor stars.

3 - The portion of the sky in the absolute vicinity of the milky way is more densely populated with bright (nearby) stars than other regions of the sky. If "when you looked up" you happened to be seeing that part, then even with "minimal" light pollution, you would not see many stars.

4 - In england, near you home, most probably, where you live, the neons may be switched off after a time at night, and "all stars" appear.

5 - In equatorial climes, especially at night a slight vapor condensation from the sky occurs, which in due course drifts landwards as "dew". This lends a certain opacity to the otherwise dark sky. This coupled with which part of the sky you happen to be looking can tend to give you the impression of "less stars". In fact if you arise early enough, this "settling" dew appears as opaque layers of mist hanging at some distance from the ground. By morning, this has settled and gives you the impression the sky was "clear" at night, which was actually otherwise.

Hope that suffices.
Jayen