Keith's astrolabes: description and use of the ecliptic circle displayed with my Java applet
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Ecliptic Circle

The ecliptic circle is the circle on a celestial sphere around which the Sun seemingly travels, making one circuit per year.

The ecliptic circle is marked with the 12 signs of the Zodiac, and each sign is divided into 30 degrees, of which only some of the graduations are usually indicated.

On the astrolabes displayed here, it has been necessary to abbreviate the names of the signs. The full names are:

Aries, Taurus, Gemini,
Cancer, Leo, Virgo,
Libra, Scorpio, Sagitarius,
Capricorn, Aquarius and Pisces.


The Sun's position

The Sun's position on the ecliptic circle can be found by first determining its current position in the Zodiac using the calendar/Zodiac scales on the back of an astrolabe. On a conventional astrolabe, the position of the Sun on the rete can then be found by finding this position on the Zodiac scale marked along the ecliptic circle of the rete. If the rete has been rotated according to the current time and date, the position of this point on the ecliptic circle can be found amidst the almucantars and elevation arcs, so that you can find the precise position of the Sun in the sky.

To minimise the time taken to find the position of the Sun on the rete, there is a menu entry which allows the scale on the ecliptic circle of the rete to show the date:

Menu: Astrolabe /Rete - Ecliptic circle /Calendar scale
This scale was included on some astrolabes. The position of the current date along that scale shows the position of the Sun on that day.

Otherwise, the approximate position of the Sun can be found by taking the point on the ecliptic circle which is aligned with the present date on the rete, but there is a slight error in doing this.

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Copyright Keith Powell 1999-2002