The Sun in September 2012

On 22 September is around 16:49 EST, the astronomical start of autumn. The sunset is the end of September an hour earlier than the first of the month - to 19 ¼ clock. Also in the morning, it is much longer dark: The sunrise is delayed until after 7 clocks.

The sundial reflects the true solar time, which can be determined from the position of the sun in our sky by direct measurements.

It is because of the periodically changing the distance of the Earth to the Sun and the tilt of Earth's axis relative to the path of the earth around the sun is not uniform - it varies more than 30 minutes from -14 to +16 minutes. It is therefore not as suitable for everyday timekeeping. For this reason, we use an "average" sun for our daily timekeeping with a fixed length of 24 hours, or 86400 seconds.

Nevertheless, the sun is just not at 12 clock in the south, that is at the highest point of their daily web: On the one hand we have the introduction of daylight saving time during the summer months only by 13 clock noon, on the other hand we do not live according to the local time, but according to time zones. Central European Time CET / CEST is the local time for cities with a longitude of 15 degrees East. Because the earth rotates around its axis in 24 hours, equivalent to a deviation from a longitude of a time difference between local and zone time of 4 minutes. For places west of 15 ° East, the sun culminates later accordingly, eg in Mannheim and Zurich, each with about 8.5 ° east longitude 26 minutes later: (15-8.5) * 4 East of 15 ° East is early "lunch": eg in Vienna 5 minutes early.

In Mannheim, the sun is at first Ie by 13 September clock up 26 minutes to 13:26 BST in the south.

Early fall

On 22 September starts at 16:49 CEST the astronomical autumn. The Sun crosses this time the celestial equator and south stands at locations on the equator at noon exactly the zenith. On the whole earth, day and night lasts the same length. This does not quite: At the South Pole, the sun rises as early as 20 September, and then, of course, is for 24 hours straight on the horizon. At the North Pole by the way the sun sets until 24 September - this because the atmosphere deflects the light beams so that we somewhat below the geometric horizon can (refraction). Just find the "true" day and night are equal, so with 12 hours instead of theoretically visible sun for our latitudes few days after the beginning of astronomical autumn, on the evening of 25 September.

Sun Run

The Kulminationshohe the sun, ie, the maximum height above the horizon at noon, when the sun is in the south reduced, during the month of September at about 11 °. Thus, even the day length shortened by nearly two hours. Thanks to the equation of time the sun is but a little less late when she goes before: In September premature in fact the true sun by more than 10 minutes compared to the "mean" sun (ie the uniform of our time clocks). This can also be checked by the following observation: sundials show now "lunch" every day at about 20 seconds earlier.