In the temperate latitudes of the northern hemisphere, the sun tracks an arc across the horizon as follows
The sun rises south of due east and sets south of due west.
Azimuth angles of ±70° are shown for sunrise and sunset. The azimuth angle changes on a daily basis.
The sun rises north of due east, crosses to the south of the east-west line during the day as it rises,
then crosses back to the north side of the east-west line as it sets and then sets north of due west.
Azimuth angles of ±110° are shown for sunrise and sunset. The azimuth angle changes on a daily basis.
The sun reaches its highest point in the sky when it is due south (geographic south, not magnetic south). This is
solar noon. In the temperate region of the northern hemisphere, the sun position will always be south of the east-west line.
For this reason, the baseline position for measuring the movement of the sun from the east to the west is established
by an observer looking due south. The angle that the observer needs to turn to look directly at the sun is the azimuth.
Before solar noon (in the morning), the observer needs to turn left. This is defined to be the negative direction of the
azimuth. After solar noon (in the afternoon), the observer needs to turn right. This is defined to be the positive
direction of azimuth.
If a line is drawn from the sun to the ground (like a ray of light), this is the angle the line makes with the ground.
Altitude is 0° at sunrise and sunset, and 90° when the sun is directly overhead. In the northern hemisphere
north of the tropic of cancer (latitude 23.45°N), the altitude always stays below 90°. Miami, Florida, at
25.8°N, has an altitude of 87.7° at summer solstice.
This is the angle of sun in the east-west direction. Geographic south is defined as azimuth=0°. Angles to the east of due
south are negative, with due east having azimuth=-90°. Angles to the west of due south are positive, with due west having
|daylight saving time
For 2006 and prior years, daylight saving time begins on the first Sunday of April and reverts to standard time on the last Sunday of October.
For 2007 and later, daylight saving time begins on the second Sunday of March and reverts to standard time on the first Sunday of November
in compliance with the Energy Policy Act of 2005.
All times reported are for United States daylight saving time, even if the location is in Canada or Mexico.
The declination relates to the tilt of the earth's axis, which is 23.45°. Declination is the angle between an earth-sun line and the equatorial
plane. The declination varies from positive 23.45° to negative 23.45° as the earth rotates around the sun.
Occurs at the beginning of spring around March 20 (vernal equinox in the northern hemisphere)
and at the beginning of fall around September 20 (autumnal equinox in the northern hemisphere).
In terms of the plots, this means that the sun is rising very close to directly east (azimuth = -90°)
and setting very close to directly west (azimuth = +90°). In spring the sun
is transitioning from rising south of due east to rising north of due east.
In fall the sun in transitioning from
rising north of due east to rising south of due east. A web search is suggested for more technical information on the equinoxes.
Sometimes called magnetic variation, it is the angle between magnetic north and true north.
True north is determined by the longitude line that runs through a particular location to the geographic north pole which
is the axis that the earth rotates around. Magnetic
north points to the magnetic north pole, which is offset from the geographic north pole and is constantly moving.
If the magnetic compass points east of true north, the declination is positive and designated as "east". If the
Magnetic compass points west of true north, the declination is negative and designated as "west".
magnetic declination is +17.6° (17.6° East) in Seattle in 2006. This means you would line up the compass
needle with the "N" on the compass and then rotate the compass 17.6° to the left (counterclockwise, toward the west) to get the
"N" pointing to true north. In Boston in 2006 the magnetic declination is -15.4° (15.4° West).
This means you line up the needle with the "N" on the compass and then rotate the compass 17.6° to the right (clockwise, toward the east)
to get the "N" pointing to true north.
For more information, visit the National Geophysical Data Center.
|percent of solar noon
This is used as a parameter in the plot specifications and varies between 0% (sunrise) and 200% (sunset). With solar noon = 100%, the sun is rising when the percent
of solar noon is less than 100% with sunrise percent of solar noon = 0%. The sun is setting when the percent of
solar noon is greater than 100% with sunset percent of solar noon = 200%.
In the northern hemisphere north of the tropic of cancer, solar noon occurs when the position of the sun is geographic south (azimuth=0°). The sun
is at its highest altitude in the sky at solar noon. Solar noon generally is not the same as noon on the clock.
Depending on location, solar noon can occur before or after 12 PM noon during standard time but is always after
12 PM noon during daylight saving time.
In some locations in summer during daylight saving time, solar noon occurs as late as 1:30 PM.
Summer solstice occurs around June 21 and is the day of the year with the longest period between sunrise and sunset.
In the northern hemisphere north of the tropic of cancer (latitude 23.45°N), solar altitude reaches its highest
point on summer solstice.
Winter solstice occurs around December 21 and is the day of the year with the shortest period between sunrise and sunset.
The maximum solar altitude during the day is at its lowest value at winter solstice.