Locations

Amateur astronomers often wonder whether there is any ideal place to live to secure good stable conditions, and I will have more to say about this later in chapter 5, "Have Webcam, Will Travel." Obviously, a high-altitude site near the equator is ideal, as the planets will then pass almost overhead and the light will pass through relatively little air. The light from a high-altitude object is also considerably less dispersed (split into colors) than from an object at, say, 20 or 30 degrees altitude. However, most amateurs simply do not have the luxury of moving abroad. Living on the slopes of a mountain or a hillside can have good and bad effects. If you go for this option you do not want to be sited on the leeward side of the hill. If the prevailing winds come from the west and you are on the east slope of a hillside, turbulent air will cascade past your observatory, wrecking the seeing. Coastal or island sites can be excellent for planetary observers, especially when the prevailing air flow is off the sea. The sea varies much less in temperature than the land and is virtually flat. A light laminar air flow off the sea can produce excellent coastal seeing, although with the risk of nighttime sea fog. Areas prone to atmospheric inversion (i.e., the temperature in the atmosphere increases, rather than decreases, through a limited layer of air) are often excellent for stable planetary observing, too. In his 1995 book High-Resolution Astrophotography, Jean Dragesco mentions peculiar atmospheric inversion conditions in Zaire that occasionally lead to temperature variations as small as 1.5°C from sea level up to the jet stream. A planetary imager's dream!

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