RedShift: Star Colors
Astronomy
Name:
Period:
Lab begins on page 202 in the RedShift Lab book
Data Table 1
Red/Orange/Yellow Stars (Hyades)
Spectral
Color
Type
Star Name
B-V
Index
Temperature
Aldebaran
K5
Orange
+1.54
4,200
75 Tau
K2
Orange
+1.14
4,800
Hyadum Ii
G8
Yellow
+0.98
5,000
the 1 Tau
G7
Yellow
+0.95
5,200
Hyadum I
G8
Yellow
+0.98
5,000
B-V
Index
Temperature
Data Table 2
Blue and White Stars (Orion)
Spectral
Color
Type
Star Name
Nair Al Saif
O9
Light Blue
–0.21
21,000
Thabit
B0
Blue
–0.26
21,000
C Ori
B2
Blue
–0.18
20,000
BSC 1942
B7
Blue
–0.11
18,000
BSC 1887
B0
Blue
–0.25
21,000
Q1.
Blue stars are the hottest
Q4.
Orange star has B – V index of +1.50
Q2.
Orange stars are the coolest (from these
lists)
Q3.
Blue star would have B – V index of –0.2
Q5.
light yellow star has B – V index of +0.4
Q6.
B – V index +0.4 star has temp. of ~6,500K
Data Table 3
NGC 3293
Rating
Color
Color
Stars
(1/4 screen)
Stars
(total)
Blue
20
80
1
White
60
240
2
Yellow or
Orange
Red or
Pink
Stars
(1/4 screen)
Stars
(total)
Rating
5
20
2
1
4
3
Data Table 4
NGC 6520
Color
Rating
Color
Rating
Blue
1
Yellow/Orange
2
White
2
Red
3
Photo
Dimensions
Length
(squares)
13 x 8
13
NGC 6520
Width
Total Area
(squares)
(squares)
8
104
Q7.
White seems the most common color
Q8.
Blue and white are the brightest stars
Q9.
The brightest stars are a lot brighter
Q10.
The hotter one is brighter (if same size)
Q11.
Blue should be brighter
Q12.
Red seems the faintest color
Q13.
Yes, lower temperature means less intensity
Temp (K)
Spectral
class
Color
>25,000
11,000 –
25,000
Number of stars Total number
per square
of stars
7,500 –
11,000
~30
~3,120
Q14.
No, a single star’s distance can’t be known
Q15.
Rare/unusual, but red stars are most common
Q16.
Answers vary; underestimating is common
Q17.
A) Most of the bright stars are the hottest
Q18.
C) Most of the dim stars are the coolest
Q19.
Orange stars disobey the rule
Q20.
White stars disobey the rule
6,000 –
7,500
5,000 –
6,000
3,500 –
5,000
<3,500
O
B
A
F
G
K
M
blue
blue
light blue
light
yellow
yellow
orange
red
Conclusion. Write your summary below.
Star color depends on star temperature. Blue stars are hotter than red stars, with yellow/orange
stars in between. The B-V index is a way of noting star color as well. Blue stars have a negative
index and yellow/orange/red stars have a positive index.
Stars types are designated by spectral classes based on temperature and color. There are 7 stars
classes named O,B,A,F,G,K,M.
When looking at the sky, blue/white stars are commonly seen, and yellow/orange/red stars are
seen less often because they are dimmer. However, blue/white stars are much more rare in the
universe. They just appear more frequently because they are brighter (more luminous).