Unit 05 Stars
Exploration 2 The Lives of Stars FYI Readings
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Name:
Hour:
Go to ebook. Iat.com and log in: username and password are both WestAstro15
Click on the Stars button on the right
Click on Exploration Two The Lives of Stars
scroll down to the correct FYI, carefully read the FYI, then go back and answer the questions.
Spectral Classification – A Look Back
1. The first effort to classify stars began in the 1890s, at Harvard College Observatory. A team of women,
headed by ________________________, classified a quarter of a million stars, and in 1918, published the
Henry Draper Catalog.
2. The spectra were originally placed in groups, labelled with the letters of the alphabet, starting with A, based
on how strong the Hydrogen lines were, but were reordered so all of the elements visible in the spectra
smoothly transitioned from one to the next. The resulting sequence of spectral classes became
__________________________________, with the O stars at one end, and the M stars at the other.
3. Each class is further divided into 10 subclasses, numbered from 0 to 9. So the B class stars are numbered
from B0, B1, B2…to B9, which then transitions to A0, A1, etc. Therefore, a B9 stars is very similar to an
________ star.
4. Besides giving us the current order of the spectral classes, Antonia Maury notices that the spectral lines for
stars in the same class were different depending on the size of the star, with larger stars having wider lines
than smaller stars. She proposed a second level of classification, termed _________________________ ,
designated by a Roman numeral for each class. The spectral class and luminosity classes were combined to
form the currently used classification system.
Spectral Classes
Luminosity Classes
Spectral
Class
O
Color
Blue
Surface
Temp (K)
28,000 – 50,000
Luminosity
Class
Description
Ia
bright supergiants
B
Blue-White
10,000 - 28,000
Ib
supergiants
A
White
7,500 – 10,000
II
bright giants
F
Yellow-White
6,000 – 7,500
III
normal giants
G
Yellow
5,000 – 6,000
IV
sub-giants
K
Orange
3,500 - 5,000
V
main sequence stars
M
Red
2,500 – 3,500
(OVER)
Unit 05 Stars
Exploration 2 The Lives of Stars FYI Readings
Name:
Hour:
5. Fill in the table below with the color, temperature, and luminosity class of the given stars:
Name
Betelgeuse
Spectral
Classification
M2Ia
Rigel
B8Ia
Mintaka
O9II
Sirius
A1V
Sun
G2V
Aldebaran
K5III
Polaris
F7Ib
Color
Temperature
Luminosity Class
Use the table above to answer the following questions.
6. Which of the stars is/are the largest? (brighter stars tend to be larger)
7. Which is the hottest?
8. Which is the coolest?
Inverse Square Law – Star Light, Star Bright: The Magnitude System
9. The brightness of an object that we perceive from Earth is called its ______________________ brightness
(how bright it appears to us).
10. The Greek astronomer Hipparchus devised a system for classifying the stars by how bright they appeared to
be to the unaided eye (telescopes wouldn’t be invented for another 1900 years!). He put the brightest stars
in the ______________ magnitude class, the second brightest in the ____________________ magnitude
class, and so on. The dimmest stars he could see were ________________ magnitude.
11. The apparent magnitude doesn’t tell us how bright a star really is because their distances from Earth aren’t
all equal. A very bright star can appear to be very dim if it is far enough away. To make the magnitude scale
more useful to astronomers, they devised the absolute magnitude scale to compare the actual brightnesses
of stars as if they were all the same distance from Earth. The absolute magnitude is a measure of the star’s
_________________________________ - the total amount of energy given off by the star each second.
(OVER)