AY Honors/Midnight Sun/Answer Key
1. Describe the geographic areas the midnight sun may be seen in.
The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the sun remains visible at the local midnight.
2. Describe why and at what time of the year the phenomenon may be seen.
Around the summer solstice (approximately June 21 in the north and December 22 in the south) the sun is visible for the full 24 hours, given fair weather. The number of days per year with potential midnight sun increases the farther towards either pole one goes. Although approximately defined by the polar circles, in practice the midnight sun can be seen as much as 90 km outside the polar circle, and the exact latitudes of the farthest reaches of midnight sun depend on topography and vary slightly year-to-year.
The phenomenon is caused by the Earth's axial tilt, which at the solstice tilts one pole away from the sun (polar night), and tilts the other towards the sun (the midnight sun). This is easily illustrated with a globe and a flashlight, by observing which parts of the globe are illuminated (or in shadow) as the globe rotates on its axis, and as the globe orbits around the "sun" (or in our case, the flashlight).
3. Find a place where you can observe the sun at its lowest position during the night and do the following:
a) Calculate the exact time for the sun's lowest position (take into consideration daylight saving time if applicable).
The sun's lowest position occurs when the sun is due north. At this instant, the shadow cast by a gnomen (a perfectly vertical pole) will point due south.
You can figure out the time that this happens at your location by using planetarium software, such as Stellarium which is free and is available for many type of computers. To do this, set your observation location to where you are, and then set the time to midnight. Check the position of the sun - is it east of north, west of north, or due north? If it's too far east, set the time a little later. If too far west, set the time a little earlier. Continue refining the time until the sun is due north.
You can also calculate the time of solar noon using charts as described at http://www.spot-on-sundials.co.uk/localtime.html - and then add twelve hours to get the time of the midnight sun.
b) Stay awake until the sun has reached its lowest position and take a landscape picture that shows the sun and some surrounding nature. Make sure not to look directly into the sun without proper protection.
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c) Look around you and take note of how the nature reacts to the continuous sunlight.
d) Find information on the time period the midnight sun phenomenon is visible at your point of observation.
4. For what period of the year is the sun visible at each of the poles?
At the poles themselves, the sun only rises once and sets once each year. During the six months when the sun is above the horizon it spends the days continuously moving in circles around the observer, gradually spiraling higher and reaching its highest circuit of the sky at the summer solstice.
The polar sunrise happens at the spring equinox, and the polar sunset happens on the autumnal equinox.
5. What is the “polar night”?
The opposite phenomenon of the midnight sun is the polar night, which occurs in winter when the sun stays below the horizon throughout the day.
