horizon sun view

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civil twilight:
0 < height < - 6 deg.

nautical twilight:
- 6 deg. < height < - 12 deg.

astronomical twilight:
- 12 deg. < height < - 18 deg.

The yellow circle

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is the image point (Geographical Position) of the sun, where the line from the sun to the center of the earth intersects it's surface. The coordinates of the sun's Geographical Position (latitude and longitude) are the same as the declination and Greenwich-Hour-Angle (GHA) of the sun.

An observer positioned in the Geographical Position will see the sun directly in the vertical, above his head.

A click into the map

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displays the red shadow of a 50 pixel vertical gnomon on a horizontal plane

.

the geographical coordinates of the clicked location

.

.elevation and azimuth

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the elevation (above horizon)

and azimuth angle of the sun
and it's direction (in brackets)

0 deg. = N, 90 deg. = E
180 deg. = S, 270 deg. = W

For a new location:

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enter latitude, and press return key
(not enter key !)

- degrees latitude as
a non-negative integer or decimal (0°to 90),
and select "N" or "S"

.

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enter longitude, and press return key

- degrees longitude as a
non negative integer or decimal (0 to 180),
and select "E" or "W"

Time Zone Offset

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time difference between zone time and Greenwich Time (GMT )

With Netscape 4 and Internet Explorer 4, the applet should display the correct time zone offset:

Central European Daylight Time = GMT + 2 hours
Central European Time = GMT + 1 hour
"time zone offset is +2 h" (for Central European Daylight Time)
If necessary, select the correct time zone offset from the menu.

delination and GHA

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the declination and Greenwich-Hour-Angle (GHA) are the coordinates (latitude and longitude) of the sun's Geographical Position (GP), where the line from the sun to the center of the earth intersects it's surface.

equation of time

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The Equation of time is the difference between the time determined by a sundial and the clock time. It is due to the obliquity and the unequal motion of the sun (ellipse).
the value is computetd for 12:00 h local time.

For detailed information:
Royal Greenwich Observatory: 'The Equation of Time'.