Sun or Moon Rise/Set Table for One Year (National Naval Observatory) – http://aa.usno.navy.mil/data/docs/RS_OneYear.php
Representative questions this resource can answer:
- When does Barrow get midnight sun?
- How much does daylight vary in Hawaii between December and June?
This is a fairly simple site. There are two online forms. The first is for US locales and can be searched by state and place name. The other is for “Locations Worldwide.” The form for “Locations Worldwide” can only be searched by latitude and longitude. The form does point to a few resources for getting latitude and longitude for non-US cities.
In either case, filling out the form provides a table of sunrise and sunsets for one full year. In addition to providing sunrise and sunset for a year, the “type of table” field allows you generate year long tables for moonrise/moonset, civil twilight, nautical twilight and astronomical twilight. The US Naval Observatory defines these twilight terms as follows:
Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.
Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible. During nautical twilight the illumination level is such that the horizon is still visible even on a Moonless night allowing mariners to take reliable star sights for navigational purposes, hence the name.
Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, scattered light from the Sun is less than that from starlight and other natural sources. For a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible.
This website was inspired in part by factual errors in the graphic novel turned movie 30 Days of Night. This site can easily illustrate that even the movie’s title is itself a factual error. An error in favor of humanity, but still an error.
Plugging in Barrow Alaska, we see that the sun sets on November 19th at 1:18 pm and rises at 1:05 pm on January 23rd. That’s 65 days of night, not 30.
Try playing with both forms on the site to see if you can find a location where the sun truly sets for 30 days. You can use Wolfram Alpha (http://www.wolframalpha.com) to calculate the number of days between the last sunset and the next sunrise.
Another problem with the movie is that these 65 days of night are not pitch black. If you choose “civil twilight” from the “type of table” field, you’ll see that there is some civil twilight every night between November 19th and January 23rd. On December 21st, the shortest day of the year in some places, there is still three hours of usable civil twilight in Barrow. Perhaps not bright enough to burn vampires, but enough for the townspeople to see them coming.
Leaving this 30 Days of Night fact check behind, this site could be useful for determining when your characters have a chance of seeing things clearly.