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About 11pm (i.e., after the end of astronomical twilight) I’d like you to go outside and make some measurements. (For town or city locations, after 10pm should be ok).
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Go to an area away from direct light, e.g. when you are out for exercise and allow some time to accommodate to the (relative) darkness (you might notice seeing some more fainter stars if conditions are good). If you need glasses for distance vision, don’t forget to use them…
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Using a toilet roll core, point to at least 5 directions (zenith plus another four at approximately 45 degrees altitude, e.g. zenith, N, S, E, W (fill in the intermediate points, i.e. NE, SE, SW, NW if you have time). As a guide, if you’re unsure about where 45 degrees is relative to your horizon (e.g. if it’s obstructed), if you can see the Pole Star, place that just above the field-of-view of the tube, and you’ll be at approximately the correct angle.
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For each position, let your eye roam around the field-of-view and note which stars you definitely see, and which you appear to see most of the time (i.e., are near the limit). If there are clouds in that direction, just skip and move on to the next area.
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Write down the date and time together with a brief note of the conditions (e.g. whether any haze), and provide the star counts against each position.
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The site where you took your measurements needs to be recorded - if you prefer not to be too specific, you can anonymise your location by CSO mapping or provide Google Map Co-ordinates for approximate position.
For More Information see -
www.DarkSky.ie