About forty-five years ago, US astronomers got together and developed Kitt Peak
ID: 112512 • Letter: A
Question
About forty-five years ago, US astronomers got together and developed Kitt Peak National Observatory near Tucson (about 32 degrees north of Earth's equator). At nearly the same time, US astronomers working in collaboration with astronomers in Chile established a comparable observatory in Chile, about 30 degrees south of the equator. Please explain (in sufficient detail to make it clear to someone with no background in astronomy) why it is that astronomers need to build telescopes in the southern hemisphere when they have some in the northern hemisphere.
Your answer should include a response to the following: The constellation of Ursa Minor is located near the North Celestial Pole, or about 80-90 degrees from the Celestial Equator. Orion straddles the Celestial equator (half N and half S), and the Southern Cross is located close to 90 degrees south of the Celestial Equator. Which constellation(s) can you observe from the observatory in Arizona? ...the one in Chile? Both observatories?
Explanation / Answer
If in the Southern hemisphere an observatory is placeed high enough so it doesn't get too affected by weather, it offers a good coverage. But you may still get some cloudy nights, and some types of observations do require regular monitoring so if you want to observe on a given place and it's cloudy there, it's as if there wasn't any telescope there, you're dependent on other sites having clear skies.
Another reason is that there are more sites with potentially clear skies in terms of light pollution, since the majority of the world population lives in the Northern hemisphere. Sure, there is also less landmass.
The third is seeing conditions. It's better to observe overhead than near the horizon, because near the horizon the light has to transverse a bigger portion of the atmosphere, therefore it gets more affected by turbulence and absorption. Overhead there's less atmosphere for light to transverse, so the images appear more steady and less affected by the water vapor and dust in the atmosphere (which produces some reddening).
The sky over Antartica is particularly dry, because all the water that could be in the atmosphere precipitates as snow. Moist air coming from the sea loses, if it precipitates, loses its moisture as it crosses the landmass. So you have a very dry air deep inside the continent.
We can observe both the constellations. Ursa minor will be far away from the north and orion appears as a bright constellation.