Obtaining site data

Users of some telescopes can pick their country or state and city from a list; the rest of us have to type in our latitude and longitude, accurate to a degree or two. Latitudes and longitudes in Britain and North America can be estimated from the maps in Figures 3.3 and 3.4. For more accurate data, consult a large-scale map or atlas, look up your location at a geographical website such as http://www.gazetteer.de, or use a Global Positioning System (GPS) receiver. Some telescopes have a GPS receiver built-in (p. 29).

Hint: Make sure you know whether you're using decimal degrees or degrees, minutes, and seconds. If your latitude is +45.75 and you enter it as 45° 75', the telescope will not accept it because the number of minutes is always less than 60.

Longitude 8° W 6°W

4° W 2° W

2° E

Most telescopes: -8° -6°

-4° -2°

+2°

Meade LX200: 8° 6°

4° 2°

358°

Figure 3.3. Latitude and longitude map of Britain.

Longitude 120°W

Most telescopes: -120° Meade LX200:120°

100-W

90" W

100-W

90" W

Longitude 120°W

Most telescopes: -120° Meade LX200:120°

U.S. Geological Survey (adapted)

Figure 3.4. Latitude and longitude map of the contiguous 48 states.

U.S. Geological Survey (adapted)

Figure 3.4. Latitude and longitude map of the contiguous 48 states.

3.4 Why compasses don't point north

Instructions for setting the clock inside specific models of telescopes are given in Part II. These clocks, like all others, are imperfect; check their accuracy every month or two. Some of them use 24-hour format (e.g., 8 p.m. = 20:00); the rest require you to distinguish between a.m. and p.m. Clearly, if you mix up a.m. and p.m., the telescope will be totally mistaken about what is in the sky.

Hint: Meade LX200 and Celestron NexStar telescopes require you to enter the date in American style - month/day/year. For example, 03/01/05 is 2005 March 1.

Meade LX200 telescopes reckon longitudes and time zone numbers in the opposite of the usual direction. Longitude -84° (i.e., 84° west) and time zone —5 (Eastern Standard Time) go into an LX200 as +084 and +05 respectively. That's because the designers of the LX200 chose to measure longitude the same way on Earth as on other planets, i.e., increasing westward all the way around to 360°.

If you wish, you can run your telescope on Universal Time (UT) regardless of your location; just enter the time zone number as 0. Be sure to give the date as well as the time in UT. For example, 8 p.m. EST on January 1 is 01:00 UT on January 2.

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