SUN EPHEMERIS

Sun data for your city

Do you want to know when it rises at your latitude and longitude? When it sets, or passes the meridian? Do you need to know its altitude, or its azimuth at a given moment of the day? Do you need its equatorial coordinates?

Well, this page does the necessary calculations and provides you with the data you need.

We thank Prof. Franco Martinelli for kindly allowing us to make the calculations.

Day

Month

Year

Hours

Minutes

Seconds

Location

Latitude

Longitude

Winter Time

Summer Time

Jet lag

When you open the page, the calculations are made for the location of Milan and for the day and time on which your computer is set.

Change the data and insert the ones you like.

Warnings for entering data

Latitude and Longitude must be entered in decimal degrees, with the – sign for longitudes east of theGreenwich meridian 0 (this data is easily available on Google Maps by clicking the left mouse button on the map, the location you are looking for).

The time zone is the one legally assigned and coinciding with that of winter time.It is expressed in hours (and possibly decimals) of difference with respect to Greenwich time (UT) with a positive sign for locations to the east, negative to the west.

For example, in Italy and in most European countries the time zone adopted is the one known as TMEC (Central European Mean Time) corresponding to one hour of difference from Universal Time (Greenwich Mean Time).

Remember to indicate whether at the moment considered summer or winter time is in effect.

There are no data acceptance controls. You can then enter latitudes greater than 90°, days beyond the 31st, and so on.Check that the data entered is correct and consistent.

The Sun

rises at

sets at

azimuth

passes through the meridian at

astronomical twilight

morning

evening

nautical twilight

morning

evening

hours of

sunshine

darkness

Its Astronomical Coordinates

Altazimuths

height

azimuth

Equatorial

right ascension

declination

hour angle

Equation of Mean Time

The Equation of Mean Time is the difference between the time indicated by our clocks and that referred to the actual position of the Sun in the sky.

Apart from its applications in Astronomy, its knowledge can be useful when reading a sundial. The indications of the latter must in fact be corrected by the Equation of Time in order to be compared with those of a clock.

When the sign is positive, the sundial advances with respect to the clock, when it has a negative sign it delays.

It is variable during the year and assumes the maximum value of about 16 minutes.

It is the time difference between the passage of the Sun on the central meridian of the time zone and the meridian of the observer.This difference is due to the fact that all the clocks of a country (within a given time zone) are set on the central meridian of the time zone rather than on the local meridian.

The maximum value is 30 minutes. If daylight saving time is in effect (since this in fact involves the adoption of a different time zone) a full hour is added to the correction.

Time Zone Correction

Julian date

To facilitate the computation of time and to free it from the irregularity of months, normal years, leap years, etc., in Astronomy the Julian Date is used.

The days are numbered progressively starting from 12 UT on January 1, 4713 BC.

The decimal part expresses the instant of the day, that is, the hour, minutes and seconds.

SUN EPHEMERIS

Orologi senza tempo