Download HR Diagrams

HR Diagrams

In the early 1900s, two scientists
named Hertzsprung and Russell each
discovered that there is a relationship
between the brightness of stars and
surface temperature. Although these
scientists did not work together, the
graph that illustrates their findings is
named after them.
Temperature

The physical properties used on the H-R diagram
are temperature, absolute magnitude, and color.
Stellar temperature is generally recorded using the
Kelvin scale. A temperature recorded using the
Kelvin scale is the temperature in Celsius + 273.
This method avoids negative temperatures. Surface
temperature determines the color of a star.
Stellar Temperature-Color Relationship
blue
25,000+ K
blue white
11,00025,000 K
white
7,50011,000 K
yellow white
6,0007,500 K
yellow
5,0006,000 K
Reddish
orange
3,5005,000 K
red
2,0003,500 K
Brightness

Absolute magnitude is the measure of light stars
generate from the surface. Since stars are different
distances from Earth, absolute magnitude is a measure
of brightness regardless of distance. An incredibly bright
star has a magnitude of –5 or more, an average star’s
absolute magnitude is close to 1, and a dim star’s
magnitude is around 10. In general, stars that are
large and hot are brighter than those that are small and
cool. Since stars change in predictable ways as they
age, 85% of stars follow this general pattern called the
Main Sequence. Most scientists consider an H-R
diagram a snapshot of the lives of stars.
Scientists classify stars according to: _______,
SIZE
_______, & ________
Temperature
Brightness
Temperature
A star’s color reveals its __________. The
RED while the hottest
coolest stars glow ______,
BLUE
stars glow ___________.
Types of Stars
Classification
Class
Temperature
Color
O
20,000- 60,000 K
Blue
B
10,000 – 30,000 K
Blue-white
A
7,500 – 10,000 K
White
F
6,000 – 7,500 K
Yellow-white
G
5,000 – 6,000 K
Yellow
K
3,500 – 5,000 K
Orange
M
2,000 – 3,500 K
Red
Q: Based on its color, is our sun very
NO
hot? ___________
Brightness
___________
of a star depends on its
Temperature
___________
and __________.
SIZE
Brightness can be measured in terms of
luminosity
magnitude
_____________or
in______________.
Luminosity
__________ is
how much power
the star gives off
as compared to
our Sun. Our
sun’s luminosity
is 1.
Magnitude is
_____________
the measure of
light stars
generate from their
surface. An
incredibly bright
star has a
magnitude of -5 or
more, an average
star’s magnitude is
close to 1, and a
dim star’s
magnitude is
around 10.