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Day 7) Star Characteristics 9.2, 9.4
Name __________________
This class is about the characteristics of stars and more importantly, how we know what we know.
1) The Sun looks much brighter than all the other stars because it is so close. It seems to have a fairly
average luminosity. Other stars have luminosities that are up to a million times greater and down to a
million times smaller. How do we know the luminosities of these stars?
Review: We measure their apparent brightness and use distance to calculate luminosity. We get distance to
nearby stars using parallax and we get the distance to more distant stars by using standard candles that are in
the same galaxy.
2) The Sun has a mass of 2 x 1030 kg and the other stars have masses ranging from 1/10th of this to over
200 times more. How do we know the mass of the other stars? This is done by measuring the period and
radii of the ___________ orbiting them.
A) moons
B) planets
C) stars
Explain:
C) Not Moons. They let us calculate planet masses. We used planets for the Sun’s mass but it is too hard to
do this with the other stars, because the planets are usually too faint to see. Fortunately, most stars have at
least one star partner.
3) The Sun has a temperature of 5506o C and the other stars range from 2000o C to 50, 000o C.
a) Where have you seen colour change with temperature? How does the colour change?
A stove element goes from black to a dark red to an orange-red. A small incandescent bulb and a
generator turned slowly will show a filament that eventually goes yellow and then white. ‘Cool’ stars are
red, average stars are yellow or white and hot stars are blue.
b) An infrared thermometer measures temperature by measuring the invisible light it produces.
Contest: Produce the coldest and hottest temperature with the materials at your desk.
Have them write down their choices and then go around and measure each. Their bodies will show a
temperature of 37o C. If they rub their hands vigorously, they can get a higher value. If they get something
wet and blow or fan air across they should be able to get a temperature below room temperature.
http://spiff.rit.edu/richmond/sne/aavso/nova_sn.html
c) The light from the two stars shown in the graph is very different. Compared to the K5V star, the
ADV star is
A) brighter, hotter
B) brighter, bluer
C) hotter, bluer
D) all three
Explain:
B) Shorter wavelengths means bluer. If it is hotter, then it also must be bluer. From 3000 to 5500, ADV
is intrinsically brighter. From 5500 to 10000, K5V is brighter. The extra area is almost the same.
4) The Sun is made of 73% hydrogen, 25% helium. How do we what stars are made of?
a) Hot gases emit a specific fingerprint of light. What are the different coloured lines that you see in
each sample? Give students diffraction gratings. Have them look at several elements in discharge
tubes. What is important is that they notice that each is clearly different.
b) The outer atmosphere of a star contains an atmosphere that absorbs light at these specific
wavelengths. Look at the graph above. The two stars not only have different temperatures, they are
made of different materials. How can you tell? This is seen where the emitted light dips. The two
graphs have very different dips.
d record what colours are present.
c) Usually the line spectra are shown in the form above. The intensity of the light is indicated by the
width of the line. The last two samples contain more than one element. What do they contain?
The top one contains H and Na. The next contains H, He and Li.
d) In the blank space at the bottom make the spectrum for a star with two different elements. Have
your partner analyse your spectrum.
Textbook Consolidation: Read pages 370 – 373. Do questions 1, 7, 8