Starshine

Question 1

Name the various groups that stars are classified into.

Answer 1

Grouped based on stellar properties, they are red giants, white dwarfs and blue supergiants.

Question 2

What is the only information we have from stars at enormous distances away from Earth?

Answer 2

The electromagnetic radiation we receive from them.

Question 3

What can the EM emissions from stars tell us?

Answer 3

Temperature, chemical composition, speed of movement, approximate age, size and much more.

Question 4

What does stellar mean?

Answer 4

“relating to a star”

Question 5

What precise measure is used by astronomers to classify the brightness of stars?

Answer 5

Luminosity, it is defined as the rate at which energy of all types is radiated by an object in all directions.

This depends upon both it’s size and temperature.

Question 6

What is a black body?

Answer 6

A perfect radiator, that will give off energy across the entire electromagnetic spectrum (a large range of wavelengths).

Question 7

What is the “Stefan-Boltzman law?”

Answer 7

This tells us that the power output from a black body is proportional to its surface area and the fourth power of its temperature in Kelvin

L=(sigma)AT^4

Question 8

What is a star’s spectrum?

Answer 8

The range of wavelengths of light given off by a star.

Question 9

What is Wien’s law?

Answer 9

(lamda max)T=2.898*10^-3

Where lamda max is the peak wavelength at which the energy output is most. It’s evident from the SB law, that as the temperature of a black body increases, so does the energy emitted.

Question 10

What can the temperature of a star tell us?

Answer 10

It determines the spectral output of the star, but it can also suggest chemical composition and age.

Because of this astronomers have classified stars into groups according to their temperature.

Question 11

How are the spectral star classes labelled?

Answer 11

By letters, (O)h (B)e (A) (F)ine (G)irl, (K)iss (M)e.

Question 12

What are the trends in hotter stars?

Answer 12

They tend to have more mass and are more luminous.

Question 13

What happens due to the large gravitational pressure at the center of a massive star?

Answer 13

The nuclear fusion reactions within the star run very fast, producing a lot of energy and using the hydrogen fuel in the star at an incredible rate.

Question 14

What are the characteristics of massive stars?

Answer 14

They are larger, and at high temperatures, the hotter stars are very luminous, giving off a great deal of energy.

Question 15

What class of stars do blue supergiants belong to?

Answer 15

O class

Question 16

What class of stars do red dwarf stars belong to?

Answer 16

M class

Question 17

What trend is seen in a graph plotted with luminosity against star temperature?

Answer 17

A general negative correlation, but when more data is added, the picture gets more complex.

Question 18

Why is it called a Hertzsprung- Russel diagram and not a graph?

Answer 18

The temperature measurements assume the star behaves as a black body.

Luminosity is not so accurate, because luminosity is a calculation that includes distance to the star, which is not so accurate.

Question 19

What is the ‘main sequence,’ in an H-R diagram?

Answer 19

The diagonal line across which most stars we observe fall. These stars exist in this state for the majority of their lifetime. They are stable stars.

Question 20

What are the main underlying features of the H-R diagram?

Answer 20

The plot is drawn with hotter temperatures on the left hand side.

There are places on the diagram which show other stages of a star’s evolution.

The top left area of the diagram is lightly populated.

Question 21

Why do we see such few blue supergiants in the H-R diagram?

Answer 21

Because they burn out in a few million years and most of them have already done so.