Sun & Earth Hablet

The Sun & Earth Hablet is a very complex hablet that can be rather overwhelming whenever it is first examined. To help with your understanding of this tool, the different aspects of the hablet that can be viewed above are explained in the table below.

Legend

Horizontal sun view

Civil Twilight:
0° < height < -6°

Nautical Twilight:
-6° < height < -12°

Astronomical Twilight:
-12° < height < -18°

The yellow circle

Is the image point (Geographical Position) of the sun, where the line from the sun to the center of the earth intersects its 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

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

The geographical coordinates of the clicked location

For a new location:

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"

Enter longitude, and press return key

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

Declination and GHA

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.

Time Zone Offset

Time difference between zone time and Greenwich Time (GMT)

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.

Elevation and azimuth

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

Equation of time

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).

Author:Juergen Giesen

Converted By: Alvil Singh (NCSA)

Converted from: http://mgw.dinet.de/physik/SunEarthApplet/sunearth.html

A Navigation Image Map. Use the links below.

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Last updated April, 1999 -- For more information on NSF's PACI program see
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NCSA Access ©1998 Board of Trustees of the University of Illinois.

Horizontal sun view		Civil Twilight: 0° < height < -6° Nautical Twilight: -6° < height < -12° Astronomical Twilight: -12° < height < -18°
The yellow circle	Is the image point (Geographical Position) of the sun, where the line from the sun to the center of the earth intersects its 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	Displays the red shadow of a 50 pixel vertical gnomon on a horizontal plane
	The geographical coordinates of the clicked location
For a new location:	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"
For a new location:	Enter longitude, and press return key	Degrees longitude as a non negative integer or decimal (0° to 180°), and select "E" or "W"
Declination and GHA	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.
Time Zone Offset	Time difference between zone time and Greenwich Time (GMT)	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.
Elevation and azimuth	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
Equation of time	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).