Page 5 - Science E-Book Prep.3 2024-2025 1st term_Neat unit 3,4

Science Department
Prep.3

*The Big Bang:

1. Before 15000 million years ago, the
universe was a gaseous ball of high
pressure and high temperature in a
small volume. It is in a constant expansion.
2. After the Big Bang, the expansion and
changing started continuous until this day.

3. Within minutes of the explosion, the
atomic particles merged together producing
helium 25% and hydrogen 75 % which
over the years produced galaxies, stars, and
the universe as we know it today.

*The Light-year:

Due to the vast distances in the universe, they cannot be measured by km,
so the distance is measured by the light-year which is the distance covered
by the light in one year. As the light speed is 300,000 km/sec so the light-
year equal 947,000 million km.

The light-year = 9.467 × 1012 Km

First Term 46