Characteristics of Stars for Philippine Grade 9 students

1. Characteristic
s of Stars

2. Objectives
2
3
1
recall what a star
is; recall that the
sun is a star and
that it is essential
to Earth’s
processes;
understand what makes
stars different from one
another; describe the
different characteristics
of stars
classify stars
according to its
characteristics and
properties

3. Stars &
Nuclear
Fusion
01

4. Stars are…..
…..massive balls of gas and plasma that emit
heat, light, ultraviolet rays, x-rays, and other
forms of radiation throughout the entire
universe. Stars are composed mostly of
hydrogen and some helium.

5. What is
nuclear
fusion?
Stars produce energy primarily
through nuclear fusion. Nuclear
fusion refers to the process where
two or more atomic nuclei combine
to form new and heavier atomic
nuclei (thus, a new element). It
releases a great amount of energy,
resulting in stars that are relatively
hot and bright.

7. —Nuclear Physics
This energy is released to
account for the loss in mass
when the two hydrogen atoms
undergo nuclear fusion.

8. A star’s
mass….
…..determines the elements produced
during nuclear reactions. For example,
small to medium-sized stars produce
energy by fusing two hydrogen atoms to
form an atom of helium.

9. For large mass stars, their cores are able to
fuse elements until iron. This results in an
“onion model” where successive elements are
fused after the other. After the elements are
fused and their fuel burned out, the “skin” is
“peeled” to make way for the next fusion of
elements.

11. Color and
Temperature
02

12. Stars emit colors of different wavelengths.
The color indicates the surface temperature
of the star.

13. Stars having higher
temperatures are bluer
in color.
Stars having
lower
temperatures are
redder in color
Stars in the middle
range temperatures,
like the sun, are white
or yellow.

14. …..is based on their spectral types. Spectral types are
also temperature measurements, but it is based on the
elements that they absorb. It uses the principle that
each element has its own unique set of spectral lines.
Spectral types utilize the appearance of specific
absorption lines from a star which is only observed at
a certain temperature range.
A more accurate
classification of stars ….

15. Scientists discovered that when a hot
solid object is heated at very high
temperatures such that it glows, it
produces a complete spectrum of light
with no dark lines. It is called a
continuous spectrum.

16. A hot solid object heated at very high temperature
produces a (a) continuous spectrum. Hot gases
generate a unique set of (b) emission lines. When
a cooler gas is placed near the hot glowing object,
it produces a spectrum with dark (c) absorption

17. In order of
decreasing
temperatures ….
......the seven main types of stars are O, B, A, F, G,
K, and M. Each stellar type is also divided into
subclasses (from 0 to 9) depending on its position
within the scale. For example, a G star can be
classified as G1, G2, G3 up to G9.

19. Size
03

20. The size of the
stars……
……is measured by
astronomers based on the
radius of the sun. The sun is
considered as a medium-
sized star with a radius of
695 508 kilometers.
Therefore, a star measuring
one solar radius has the
same size as the sun.

21. Stars that are much larger than the sun are
referred to as giant and supergiant stars. Most
stars such as the black and white dwarf stars
are much smaller than the sun. They are
approximately about the size of Earth.

22. ……are referred to as giant and
supergiant stars.
Stars that are much
larger than the sun……
…..such as the black and white
dwarf stars are much smaller
than the sun. They are
approximately about the size of
Earth.
Most stars…..

23. Mass
04

24. …..the mass of stars is also
measured based on the mass
of the sun. A star with a solar
mass of 1 has the same size as
the sun which is equivalent to
1.989×10^30 kilograms.
Just like its
size….

25. For example, Sirius B has
approximately the same mass as the
sun at 1.00 ± 0.02 solar mass. Rigel
has 17 times the mass of the sun.
Because of this, it also produces 66 000
times the energy produced by
the sun.

27. Brightness
04

28. The brightness of a
star…..
….…is dependent on its size and
temperature. The two ways to describe
the brightness of a star includes apparent
brightness and absolute brightness.

30. The apparent
brightness
……
….or apparent magnitude (m) of
a star is the star’s brightness as
seen from Earth. It depends on
the location of the observer.
Therefore, different observers
may measure different degrees
of brightness based on their
location and distance from the
star.

31. The apparent brightness of
the object is measured……
….such that the lower the value, the brighter
the object. Negative values indicate extreme
apparent brightness. For example, the sun has
an apparent magnitude of –26.8 while
Betelgeuse has +0.50. It means that the sun
appears brighter than Betelgeuse as seen
from Earth.

32. To measure the true brightness of a
star, a convention was established
where the difference in location was
factored out. It was done through the
use of the absolute brightness of a star.

33. …..or absolute magnitude (M)
is the brightness a star would
have if all stars were located at
a standard distance of 32.6
light-years or 10 parsecs from
Earth. It does not consider the
distance of a star from Earth.
This allows astronomers to
compare the brightness of
stars.
The absolute
brightness ….

35. —Astrophysics
The unit used in measuring the distance
between stars is called the light-year. A
light year refers to the distance traveled
by light in one year. A light year is
equivalent to 9.5 x 1012 kilometers.

37. Absolute brightness is related to the star’s
luminosity. Luminosity is the total amount of
energy radiated by the star per second. A star
is luminous when it is hot, large, or both. This
means that a small, hot star can have the
same luminosity as a large, cool star.

38. The star’s luminosity can be
deceptive. It is because stars
do not only radiate energy as
visible light.

40. ….is the best way to compare the brightness of the star today, it
also has limitations. First, astronomers should indicate which
wavelength they are using to calculate the absolute brightness of
the star. Remember that stars emit radiation in several forms
such as infrared, visible light, or X-rays. Stars can be bright in
some of these wavelengths while appearing dim in others. Lastly,
the sensitivity of the instruments being used such as telescopes
should also be considered.
Even though absolute
brightness ….

41. Key Points
Stars are defined and
classified based on their
physical characteristics. It
includes color and
temperature, size, mass, and
brightness.
Stars observed are
described by its
different
characteristics
One of the notable
ways to describe a
star is by analyzing
its spectral
signature:
through this, one
can analyze and
obtain its
composition and
characteristics.

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