# Practical exercise 2: HOW BIG ARE THE STARS?

This exercise is an adaptation of those one suggested from the educational portal of NASA:

https://imagine.gsfc.nasa.gov/educators/lessons/star_size/

## Aim

During this exercise the students will have an idea about the sizes of stars and will understand the relation between mass and radius of stars.

## Necessary materials

• the table with data,

• calculator.

## Instructions for the teacher

This exercise will give opportunity of the students by using data for specific stars to understand how different are stars according their sizes, masses, radii, density and how these parameters are connected between each other. You can create some preliminary idea by using this picture illustrating the size differences in star:

For the purpose of the exercise the teacher should give the students the text table containing stars of different types from the Hertzsprung-Russell diagram with data about their radii, masses and densities comparing the Sun.

 Star Radius (Solar radii) Density(Solar density) Mass(Solar mass) Supergiants Antares 776 0,00000004 20 Beta Lirae 19,2 0,0014 9,7 Betelgeuse 1 000 0,0000005 10 Deneb 96 0,00002 20 Gamma Cygni 67 0,00007 20 Rigel 78 0,00004 20 Giants Aldebaran Arcturus 35 0,00018 8 Beta Pegasi 40 0,00014 9 Capella 13 0,00096 2,1 Main sequence stars Our Sun 1,0 1,0 1,0 Altair 1,6 0,415 1,7 Barnard’s star 0,15 53,3 0,18 61 А Cygni 0,7 1,69 0,58 Hadar 22 0,0023 25 Kruger 60 0,35 6,30 0,27 MU-1 Scorpii 5,2 0,1000 14 Procyon A 2,6 0,102 1,8 Sirius A 1,9 0,335 2,3 White dwarfs 40 B Eridani 0,018 71,000 0,41 Sirius B 0,022 90,000 0,99 Van Maanen star 0,007 47,000 0,14

## Detailed instructions for the students

Arrange the stars from the list according their radius starting from the smallest to the largest one.