# Perihelion Day

PUBLISHED : Wednesday, 05 January, 2011, 12:00am
UPDATED : Wednesday, 05 January, 2011, 12:00am

## Share

Special day

On Monday, the earth was at its closest position to the sun in its year-long journey through the solar system. This special day is called Perihelion Day.

The name 'Perihelion' comes from the Greek word 'peri' meaning 'near' and 'helios' meaning 'sun'.

Ellipse

We know that planets do not follow a circular path around the sun. They move around the sun in a stretched-out circle called an ellipse. This means that the distance between the sun and the earth is different at different times of the year.

Johannes Kepler

German maths teacher Johannes Kepler (1571-1630) was the first person to realise that the planets do not travel in a circular orbit around the sun.

Some scientists thought that some planets moved backwards in their orbit. They found this to be strange.

Kepler was able to explain what really happens. He thought he had discovered God's mathematical plan for the universe. He made what we now know as 'Kepler's Three Laws' of planetary movement.

First Law

Kepler's first law says that the planets' orbits are ellipses which have the sun as their focus.

Aphelion

The opposite of Perihelion days is Aphelion Day. This is when the earth is as far away from the sun as possible during its orbit. The 'Aph' part of Aphelion comes from the Greek word 'Apo' which means away. Aphelion Day is usually on July 7.

Now do this

1 In which month is Perihelion Day?

a. January

b. June

c. July

2 Who discovered elliptical orbits?

a. Joseph Kramer

b. Johannes Kepler

c. John Krause

3 What is the opposite of Perihelion Day?

a. Antihelion Day

b. Aphelion day

c. Apron Day