![]() Follow Starry Night on Twitter Follow us Facebookand Google+. This article was provided to by Simulation Curriculum, the leader in space science curriculum solutions and the maker of Starry Nightand SkySafari. Surprisingly, a number of dedicated deep-sky observers live in Canada's prairie provinces, and have logged large numbers of deep-sky objects despite the challenges of observing in the summer "twilight zone." I first met him at the solar eclipse in Libya in 2006. I have an astronomer friend who lives in Yellowknife in Canada’s Northwest Territories, latitude 62 degrees north. So what do northern astronomers do in the summertime? Aside from observing the sun, they do very little. The situation is not as bad in the Southern Hemisphere, as there are only a handful of cities south of 45 degrees south. There, at midnight local time in midsummer, the sun is only 12 degrees below the horizon, still in nautical twilight. I discovered this myself when visiting Cumberland in northern England as a teenager. In Europe, things are even worse, because the major population concentrations in that continent are much farther north than in North America. Then, you can see the problem facing astronomers in northern latitudes. It marks the end of civil twilight, which begins at sunset. This means that for several weeks in midsummer, the sky never gets completely dark there.Ĭonsider that some of the finest deep-sky objects are in the constellations Scorpius and Sagittarius, which reach their highest points only in June and July. At civil dusk, the center of the Suns disc goes 6° below the horizon in the evening. ![]() In fact, the sun never gets further than 13 degrees below the horizon on the summer solstice night in this city. When Edmonton viewers look at the altitude of the sun during the night, they find that it never gets even close to 18 degrees below the horizon. Moving even farther north to Edmonton, Alberta, latitude 54 degrees, sunset is at 9:07 p.m. In Seattle, latitude 48 degrees north, sunset is at 9:10 p.m. So, at the latitude of New York, astronomers can see a totally dark sky at midsummer for less than 5 hours.Īs you move farther north, the summer twilight gets longer, and the length of total darkness shorter. But the sky in this city (without light pollution) is only fully dark with the sun more than 18 degrees below the horizon, between 10:37 p.m. ![]() In the summer, the sun rises at 5:25 a.m. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, the illumination is such that large objects may be seen but. Defined as the instant in the morning, when the centre of the Sun is at a depression angle of six degrees (6°) below an ideal horizon. Let's look at one example, New York City, which is at latitude 41 degrees north, about average for the United States. Civil twilight Beginning of morning civil twilight. The farther north one travels, the shorter the summertime darkness becomes. The sun doesn't dip quite so far below the horizon, and as a result, the length of time during the night when the sky is totally dark is much shorter than in winter. ![]() In summer, the days are longer and the nights are shorter than in winter. The Earth is tilted on its axis, which means that when the Northern Hemisphere points toward the sun and experiences summer, the Southern Hemisphere points away from the sun and experiences winter. ![]()
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