You are drawing Audrey Hepburn · 4 May 1929 · 03:00 · Ixelles Print my documents

Level 1 · Get ready · Lesson 3/3

From your clock to Greenwich

The first number of every chart: the birth time in Universal Time. Watch out for summer time.

One clock for the world

Everything is printed for Greenwich

Birth data and atlas

Name: Audrey Hepburn
Date: 4 May 1929
Local time: 03:00
Place: Ixelles, Brussels, Belgium
Latitude: 50°50′ N
Longitude: 4°22′ E
Time zone: Greenwich time (UTC+0)
Summer time: in force (1 h ahead)

Ephemerides are printed for the time of Greenwich, called Universal Time (UT). So the first job is to turn the birth time on the local clock into UT. Here is the birth data of the chart you are drawing.

Everything is printed for Greenwich

Ephemerides are printed for the time of Greenwich, called Universal Time (UT). So the first job is to turn the birth time on the local clock into UT. Here is the birth data of the chart you are drawing.

Four moves

Always in this order. Write each line on your sheet.

Summer time, the classic trap

Summer time puts the clocks one hour ahead, so a birth time read on the clock is one hour ahead of the real time. An example with Audrey Hepburn: in 1929 Belgium lived on Greenwich time in winter, and summer time had started on 21 April. So her 3:00 on 4 May was really 2:00 UT. Forget that one hour and the sky turns by 15 degrees: a different rising sign comes fast.

Find the Universal Time

Use the birth data above. Work it out on paper, then type the UT time.

Now in decimal hours

Later steps multiply by this time, so write it as a decimal: hours plus minutes divided by 60. 2 h 30 becomes 2.5, and 14 h 45 becomes 14.75.