Cambridge IGCSE Physics 0625

Topic: 6.2.2 Stars

Objective: Know that one light-year is equal to 9.5 × 10^15 m

This section focuses on understanding the vast distances in space and the unit used to measure them ÔÇô the light-year. It is crucial for comprehending the scale of the universe and the distances between stars and galaxies.

What is a Light-Year?

A light-year is the distance that light travels in one year. Since light travels at a constant speed, this provides a convenient way to measure incredibly large distances.

Calculating the Distance in Light-Years

The value of one light-year is approximately 9.5 ├ù 10¹⁵ meters. This can be expressed in other units as well.

Conversion to Other Units

Let's convert this value to kilometers and astronomical units (AU):

• Kilometers: 1 light-year = $9.5 \times 10^{15}$ m = $9.5 \times 10^{12}$ km = 9.5 trillion km
• Astronomical Units (AU): 1 AU is the average distance between the Earth and the Sun (approximately 1.496 ├ù 10⁸ km). To convert light-years to AU:

  1 light-year = $\frac{9.5 \times 10^{12} \text{ km}}{1.496 \times 10^{8} \text{ km/AU}} \approx 6250$ AU

Table Summary

Understanding the concept of the light-year is fundamental to understanding the scale of the universe and the distances involved in astronomy. It allows us to appreciate the immense distances between stars and galaxies.