Of course, a lot depends on where you actually live; an amateur astronomer in the U.S. is unlikely to prefer a Mediterranean destination to a Caribbean one unless he or she wants to combine a European/north African sightseeing trip with a bit of astronomy. The requirement is, of course, to head closer to the equator so that the planet is higher up. Also, a site that enjoys clear skies much of the time is essential, as is a site renowned for its good seeing. As we are planning on heading nearer to the equator we should have little concern about nighttime temperatures, unless we are fortunate enough to have access to a high altitude site. On this point it is surprising how cold it gets once you have ascended a few thousand feet above sea level. If you are planning a high-altitude session, also bear in mind that most people will become quite breathless if they are working hard at above 7,000 or 8,000 feet. Sadly, there have been a few fatalities over the years when unprepared explorers and amateur astronomers have ascended to high altitude at night, become cold, confused, and disoriented, and then attempted to drive back down icy mountain roads with an icing up windscreen. Never overestimate your ability to perform in freezing temperatures and at altitude, and make sure wind-proof thermal clothing is packed and suitable (Figure 5.1). For planetary observing, where transparency is not critical, the pleasant nighttime temperatures at sea level, near the tropics will result in far more being achieved before fatigue sets in (Figure 5.2).
Locations that are close to the sea are frequently favored as far as good seeing is concerned, providing one is not on the leeward side of an island under the turbulence cascading down the central hills or mountain. It is far better to be on the side of the island where a laminar air flow coming in off the sea hits the land i.e., on the windward side. However, in truth, it is far better to be in a situation where there are zero winds from ground level to high altitude. This stable situation virtually guarantees good seeing. The sea is a huge reservoir of heat and so tends to prevent huge day- and nighttime temperature variations, ideal for good seeing. In a perfect world, the dream planetary imager's island would have the same sea, air, and land temperature, day or night. If you are surrounded by water this helps considerably in that regard.
Florida, especially along the coastal region, is renowned for good seeing. The southern tip almost reaches down to a latitude of 25° north; a vast improvement if you come from the northernmost U.S. Go further south and you come to the islands of the Caribbean; beautiful tropical island paradises and with the planets even higher up and renowned seeing. What could be better?
Of course if you are keen to search out the very best sites on Earth, for good seeing and clear skies, you need do nothing more than search out where the best professional observatories are. Professional astronomers spend years searching out the best sites, for seeing, low rainfall, low humidity, and darkness, and most of these high-altitude sites are excellent for planetary work, except from the viewpoint of their accessibility, low oxygen, and cold night temperatures. (Incidentally, high humidity is often good for planetary conditions, but low humidity is indicative of a dry, rain-free and cloud-free site.) ESO's Cerro Paranal Observatory in the Chilean Atacama desert typically experiences 0.6 arc-second seeing but, in Europe, the famous Pic du Midi Observatory in the French Pyrenees also fares well. Jean Dragesco, in his excellent 1995 book High Resolution Astrophotography, pointed out that the climates of a number of countries in equatorial Africa were excellent for planetary photography, although a lot depended on precisely where the observer was located and what the season was.
For the northern European astronomer, the island of Tenerife is a cheap holiday destination with regular flights and a professional observatory established on the slopes of Mt. Teide. U.K. planet expert Damian Peach spent a year on Tenerife and secured some of the best Earth-based Jupiter and Saturn images during that time. However, as I have already mentioned, Damian did find that the seeing was far from excellent on many nights. The real advantage was the number of clear nights and the fact that the planets were so high up that atmospheric dispersion was not an issue (both Jupiter and Saturn were at a declination of +20° during that year, so they passed almost overhead from Tenerife). The neighboring island of La Palma is an even better site, although has fewer flights to it because it is not a major tourist resort in the category of Tenerife. The U.K.'s William Herschel Telescope is located at altitude on La Palma and the seeing from that site is exceptionally good, which is why it was selected. If you can travel to a site where a professional observatory is situated you can virtually guarantee that seeing conditions will be good, however, you will have to get permission first. Not surprisingly, the world's major observatories have strict regulations about the use of flashlights close to their facilities when they are trying to image stars of magnitude 27 or 28! If you live in the U.K. and regularly check the weather for signs of a high-pressure system or some good atmospheric stability you will not fail to spot that the Azores enjoy more than their fair share of high-pressure systems. Indeed, weather forecasters frequently refer to an "Azores high." In winter they seem to stubbornly refuse to settle over the U.K., and when they do they are frequently cloudy highs or highs west of Ireland feeding bitterly cold northerly air across the U.K. They seem to like to settle over the Azores themselves! Further down, and not too far from Tenerife, the island of Madeira has long been a favorite destination for planetary observers, even in the 1800s. Madeira has one of the most equable climates of any place in the Atlantic Ocean, with day (and night) temperatures at sea level, throughout the year, rarely dropping much below 20°C or rising much above 30°C. The British Victorian Astronomer Nathaniel Green made a special trip to Madeira in 1877 to observe Mars at its closest. Observing from the hills east of the capital Funchal (at an altitude of 1,200 feet) Green observed Mars on 26 out of 47 nights and described 16 nights as being either good, excellent, or superb. If Green could transport a substantial 33-cm reflector to Madeira in 1877, 21st century amateurs should, perhaps, not complain about carting a lightweight Schmidt-Cassegrain a similar distance.
Unlike the situation in 1877, the modern amateur only has to spend a few nights on the Internet downloading weather statistics to form a pretty good opinion of how suitable a site is for observing from. Indeed, these days it is very likely that other experienced amateurs can advise on the weather and seeing prospects for most obvious locations.
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