Stars and constellation

2020
Stars areare
• Stars huge
hugespheres
spheres ofof glowing
glowing gas. gas.
They They
are made
up mostly of hydrogen and some helium, and they
are produce
made up mostly
their of nuclear
energy by _____and some____,
fusion.
and they produce their energy by ________
 STAR
Stars are huge spheres
of glowing gas. They are
made up mostly of
hydrogen and some
helium, and they
produce their energy by
nuclear fusion.
What is a star?
• A star is an enormous glowing ball of hot gas.
There are billions of stars contained in the
galaxies of the universe. The Milky Way is the
galaxy where our solar system belongs. All the
individual stars you see in the night sky are
members of our galaxy.
where a star is born
A star is born

• Maybe you are wondering how a star is formed. Aside

from billion of stars, all galaxies contain huge clouds of gas
and dust called nebulae. According to scientists, it is in a
nebula where a star is born.
• The formation of a star starts when hydrogen gas is pulled
into the spinning clouds of nebula. As the clouds spin, the
atoms of the hydrogen gas collide. With this, friction heats
other gases in the cloud and the temperature in the
center of the cloud rises. This give rise to a protostar.
• The protostar starts to expand and contract. The temperature
reaches a point where nuclear fusion begins to take place.
Nuclear fusion is the reaction that converts hydrogen atoms
into helium atoms releasing a tremendous amount of heat,
causing the gas to glow. When the mass at the center becomes
stable, it now becomes the main-sequence star that will
continue to glow for millions or billions of years.
• To become a true star, Protostar must be at least 80 times as
massive as Jupiter.
How long will stars live? Do they
get old?
How long will stars live? Do they
get old?
• After perhaps billions of years, the nuclear fuel of a star, which is the
hydrogen, runs out. When this happens the star expands while the
core contracts. The star now begins to glow red.
• The star is considered old when it has reached the red giant
phase that eventually explodes and turns into a dim, cool object. The
collapse and explosion of a not so big star is called nova, while the
explosion of a massive star is called supernova. However, some red
giant stars undergo a nonexplosive fashion. These stars become
planetary nebulae.
•
Stars destiny

* the destiny of a star depends on how massive it is. When the last of the
hydrogen gas in the outer shell of a star have a mass equal to or less than
the mass of the sun, it becomes a white dwarf. A white dwarf star is
extremely dense and shines with a white, hot light. When a star that has a
mass equal to 2 or 3 times the mass of the sun runs out of hydrogen, it
becomes a neutron star. A neutron star is an extremely dense star
composed of tightly packed neutrons formed by the welding together of
protons and electrons. The more massive the star is, the more dramatic its
end will be. A massive star that has a mass equal to 3 to 4 times the solar
mass becomes a black hole when no nuclear fuel is available to support its
core. A black hole is a region in space where light cannot
Why do stars twinkle?
Why do stars twinkle?

• Do you know that stars do not twinkle? They

seem to twinkle when we see them from the
earth’s surface. The light of the stars is bent or
refracted as it travels through the thick layers of
the earth’s atmosphere. This bending of light
results in the twinkling of the stars.
•
Why do you not see stars in the
daytime?
Why do you not see stars in the
daytime?
• During daytime we cannot see any star other
than the Sun. Yes, our own sun is a star. This is
the nearest and brightest star to earth. This is
the only star we can see during the day. As the
Sun lits up the sky, more light is coming from the
sky than from the stars. But though you can’t see
other stars during the day, it does not mean they
are not there.
what star is nearest to earth?
what star is nearest to earth?

• Other than the sun, the Proxima Centauri is the nearest star
to earth. It is 4.3 light years away from earth. A light year is
the standard unit of distance for deep sky objects. It is the
distance light travels in a year, or about 10 trillion kilometers.
• To give you an idea of how far Proxima Centauri is, let
us say you will go there with a speed of 300, 000 kilometers
per second, which is the speed of light. At this speed, it will
take you more than 4 years and 3 months to reach the place
 Listed below are some stars with their distances from
earth.
Star Name Distance from earth

Sirius 8.6 light years

Vega 26 light years

Betelguese 300 light years

Deneb 400 light years

Rigel 540 light years

How bright are the stars?
How bright are the stars?

• Star brightness is described in terms of magnitude.

The brightness of a star as seen from earth is called
apparent magnitude, while its true brightness is
called absolute magnitude. The magnitude sequence
for stars starting with the brightest is … -2, -1, 1, 0,1,
2, 3, 4, 5, 6, 7, magnitude…etc. The brightest stars
have the largest negative numbers. Dimmer stars are
positive numbers.
 • For example, a star of magnitude 1 is brighter than a star of
magnitude 2. While a star of magnitude -2 is brighter than a star of
magnitude -1.
Star Name Magnitude
•
Sirius -1.47

Vega -0.00

Rigel 0.15

Betelguese 0.43

Deneb 1.25
Do you know the color of the
stars?
Do you know the color of the
stars?
• Did you know that the color of the star indicates its temperature?
Astronomers can determine the surface temperature of a star by
measuring its color. They use different methods in determining the
temperature of stars. One method is the use of an instrument called
photometer. A photometer consists of three filters that transmit light
in three different wavelength ranges. Then the scientists compare the
two neighboring wavelength bands to determine which is brighter
and they convert the color relationships to temperature. Blue stars
are hotter than red stars. Rigel is an example of a bright blue star
while Betelguese is a bright red star.
 Approximate Average Average Average
Star
Color Surface Mass (The Radius (The Luminosity Main Characteristics Examples
Type
Temperature Sun = 1) Sun = 1) (The Sun = 1)
Singly ionized helium lines (H
I) either in emission or
O Blue over 25,000 K 60 15 1,400,000 10 Lacertra
absorption. Strong UV
continuum.
Neutral helium lines (H II) in Rigel
B Blue 11,000 - 25,000 K 18 7 20,000
absorption. Spica
Hydrogen (H) lines strongest for
A Blue 7,500 - 11,000 K 3.2 2.5 80 A0 stars, decreasing for other Sirius, Vega
A's.
Blue to Ca II absorption. Metallic lines Canopus,
F 6,000 - 7,500 K 1.7 1.3 6
White become noticeable. Procyon
Absorption lines of neutral
White to
G 5,000 - 6,000 K 1.1 1.1 1.2 metallic atoms and ions (e.g. Sun, Capella
Yellow
once-ionized calcium).
Orange Metallic lines, some blue Arcturus,
K 3,500 - 5,000 K 0.8 0.9 0.4
to Red continuum. Aldebaran
0.04 Some molecular bands of Betelgeuse,
M Red under 3,500 K 0.3 0.4
(very faint) titanium oxide. Antares
Class Temperature Star Color

O 30,000 - 60,000 °K Blue

B 10,000 - 30,000 °K Blue

A 7,500 - 10,000 °K White

F 6,000 - 7,500 °K White (yellowish)

G 5,000 - 6,000 °K Yellow (like the Sun)

K 3,500 - 5,000 °K Orange

M 2,000 - 3,500 °K Red

How hot is a star?

• Always remember that the temperature of a star depends on its

original mass when it was formed. In general, the more massive a
star is, the hotter its surface. Stars have temperatures between
about 2,600 degrees Kelvin and 50,000 degrees Kelvin. Our sun has a
surface temperature of 5,780 degrees Kelvin.
• One of the most important tools of astronomers is the
Hertzsprung-Russel diagram or simply called H-R diagram. It was
developed by a Danish astronomer Ejnar Hertzsprung and an
American astronomer Henry Norris Russel. The H-R diagram is a plot
of different stars indicating their brightness versus their
temperatures.
How hot is a star?
•A popular mnemonic for
remembering this order is
"Oh, Be A Fine Girl, Kiss
Me".
• Stars are classified by their surface
temperature, that is associated to specific
spectral patterns. An early schema from the
19th century ranked stars from A to P, which
is the origin of the currently used spectral
classes. After several transformations, today
the spectral classification includes 7 main
types: O, B, A, F, G, K, M.
What is a constellation? Who discovered the
constellation?

• A constellation is the name given by our

ancestors to special groups of stars.
Constellations are invented rather than
discovered. Different cultures have made up
different constellations based on their
interpretations of the images they see in the sky.
•
 Directions: Read the story and answer the
questions.
Juanito is a mountain climber. One starry night, while
resting on top of the mountain he climbed, he noticed the
different sizes and colors of the stars. He also observed that
stars change its locations. There are also blue, red, yellow,
and orange stars. Some stars are big others are others are
small. While other stars are bright the others are dim. Juanito
was so amazed by the appearance of stars in the night sky .
•Guide Questions:
• 1. Give the reason why there is a possibility that the stars
that Juanito saw as a bright star is not actually bright.

• 2. Will the position of the stars that Juanito observed

remain throughout the night? Give your reason.
• the next slide will help you to answer these questions.
• Read Me:
• There are two factors that affect the
brightness of stars
• 1. Apparent brightness which means the
brightness of stars as seen from the Earth and
number
• 2. Absolute brightness means brightness of star
would have if all stars were the same distance
from the sun.
• Polaris is commonly known as the North star, is the
brightest star in the constellation Ursa Minor (Little
Dipper).
• The rotation of the Earth on its axis causes the
apparent nightly movement of the stars across the
sky. The revolution of the Earth is responsible for
the changing constellations in the different times of
the year.
• As the Earth rotates with an axis that is
pointed in the direction of the North Star, stars
appear to move from east to west in the sky.