Daily Drift in Star Rise and Star Set
Definition: [Astrology Cycles] The stars set almost four minutes earlier each night than the previous night, and hence they rise about four minutes earlier each evening at dusk. This drift in the setting and rising times of the stars is equal to the Mean Solar Day minus the Sidereal Day, i.e. 3 minutes 55.91 seconds.
Four Minute Drift in Star Positions. Taking the example of the eastern horizon at dusk. |
Further Information: Stars appear to rise and set because of the spin of the Earth. The reason the stars set and rise a little earlier is the Earth's rotation around the Sun. In the course of a day the Earth rotates around on its own axis once, but also moves roughly a three-hundred and sixtieth around its orbit of the Sun. So exactly one day later the view of the stars is not exactly the same, as the Viewpoint of the stars has moved by that fraction of the Earth's orbit. If you multiply four minutes by the [Babylonian approximate year of 360 days] the result is a full day. In other words a year later the cycle will have repeated itself, going around a full day, and the star will heliacally rise once more at the same time as it did a year earlier - allowing for the Movement of the ages. See Viewpoint for more information. Shown left is an example of this for the eastern horizon at sunset. At dusk the next day - because of the Earth's movement - slightly different stars will be visible on the eastern horizon |
© Dr Shepherd Simpson, Galactic Astrologer
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