Download Unit 3 - Section 9.2 2011 Star Characteristics0

Grade 9 Academic Science – Unit 3 Space
Characteristics of Stars
Section 9.2 Pages 370-373
All stars twinkle. After that, there are many visible differences such as colour and brightness, as
well as measurable differences including temperature, mass and elemental composition.
Star Characteristics
Characteristic
“Sub-Characteristics”
Star Brightness
Description
Luminosity

Total amount of energy produced by a star per
second

Measured by comparing it to the luminosity of the
Sun set at 1. Sirius has a luminosity of 22
meaning it gives off 22X more energy per second
than the Sun
Distance
Apparent Magnitude

Luminosity is stronger if an object is closer. Why?
The light is more concentrated when an object is
close. Thus, the object appears brighter.

Closer stars will appear brighter
Brightness of star in the night sky as they appear from
Earth
The scale goes from bright (1) to faint (6). A low value of
Apparent Magnitude means the star is close to Earth,
while a high value means the star is far away.
Absolute Magnitude
Brightness of star in the night sky as if they were 33 ly
away from Earth. Why? It allows us to differentiate
between low-energy emitting stars and high-energy
emitting stars over varying distances
As above, the LOW value means a brighter star.
See Table 1 on Page 371 to compare Apparent
Magnitude with Absolute Magnitude
Star Colour and
Temperature
Colour measures a star’s surface temperature.

Blue is relatively hot

Red is relatively cool

Yellow is a mid-range temperature. Our Sun is
6,000OC and appears yellowish-white
See Table 2 on Page 372 to compare star colours and
surface temperatures.
Elemental
Composition
Composition is determined by looking at the light emitted
by the star. Each element has a unique number and
configuration of electrons. These features means an
element produces only certain wavelengths of colour.
Thus, the light energy emitted by the star has its own
unique spectral pattern.
A SPECTROGRAPH is used to determine a star’s
composition. A star’s spectral pattern is compared to the
known spectra of the elements. If commonalities are
detected between patterns, the star must contain that
element.
For practice with spectral patterns, see the activity below
using Figure 1.
Solar Mass
Solar Mass is a value used to describe the masses of
galaxies and stars OTHER THAN our Sun.
Our Sun’s mass is 2 X 1030 kg. Other star masses are
compared to the mass of our Sun.
NOTE: Mass does not always reflect size (e.g., Large
mass does not necessarily mean large sized star)
Long-Distance Chemistry
Analyzing Spectral Patterns to Identify Star Composition
How do you know the chemical composition of a star? Each element has its own unique spectral pattern.
Why? Each element has its own unique number AND arrangement of electrons.
Methods
1. The figure displays the spectral patterns for five elements. What do the patterns tell you?
2. There is also a spectral pattern for the Sun. What is the elemental composition of the Sun?
3. There are three “mystery stars.” Using a ruler, line up the spectral patterns of the elements to the
mystery stars.
4. Answer the following questions.
a. In which two mystery stars is calcium present?
b. Only one mystery star contains mercury (Hg). Which one?
c. Which mystery star’s composition is LEAST like that of the Sun?
d. In a brief paragraph, describe how a star’s elemental composition can be inferred by
investigating its spectral pattern.
To practice spectral analysis, go to the Exploring Earth website at
http://www.classzone.com/books/earth_science/terc/content/investigations/es2803/es2803page02.cfm
NOTE: You may have to install Shockwave to use this interactive demonstration
Figure 1. Spectral Patterns for five elements, our Sun and three mystery stars
Homework and Practice
 Page 373, Questions 1,2,5-7,9