Night Lanterns

(A Look on Stars)

Teacher’s Guide for DiscussionLesson 3.1: ConstellationGrade 9, Quarter 3

Ma. Rachel B. EspinoTeacher I

Buhatan NHS; Sorsogon City

Suggested Motivation:

Watch video: http://youtu.be/yCjJyiqpAuU

Guide Questions: Have you ever wondered what stars

really are?

What is your idea about stars?

The Star

A star, as astronomers define it, is an object that is massive enough to convert hydrogen into helium as its primary source of energy.

It is a massive shining sphere of hot gas. Of all the stars in the universe, our Sun is the nearest to Earth and the most extensively studied. The stars visible to the naked eye all belong to the Milky Way Galaxy, the massive ensemble of stars that contains our solar system.

The Sun

The sun is a star. It is a glowing ball of gases; 1, 393, 000 km in diameter and has a mass of 2.0 x 1030 kg about 330, 000 times that of the Earth. This massive ball of gases rotates from East to West about an axis that is approximately aligned with the Earth’s. Its rotation is interesting because it rotates more rapidly at its equator than at its poles.

The Sun has a temperature ranging from 6,000°C at its surface to around 15,000°C in its center. Pressure is also enormously high in its center. In these extreme conditions at the center of the Sun, hydrogen nuclei are fusing into helium in a process called nuclear fusion. The Sun therefore is a star since it is able to convert hydrogen into helium to generate tremendous energy in the form of light and heat. It is this energy that powers the entire solar system (solar energy).

The Sun is a yellow dwarf star. Like all other stars, it will not last forever. It has been producing light and heat, powering the Solar System for the past 5 billion years. Scientist predict that in another 5 B years, the Sun will die a stellar death. By then, it shall have used up all the hydrogen in it transforming it to helium. By then, its power generating nuclear fusion shall stop.

The Sun as seen on earthThe photograph of the Sun in

outer space (NASA)

Life and Death of Stars

Huge clouds in the outer space are the starting material of a star. If adequate number of atoms are present in the cloud, then the gravitational pull is strong enough for the atoms to come together and start to contract. It forms a radiating ball to contract. It forms a radiating ball called a PROTOSTAR.

Towering pillars of gas and dust in an interstellar cloud known as the Eagle Nebula (below) contain PROTOSTARS (circled). These are newly forming stars as revealed in a photograph taken by the orbiting Hubble Space Telescope. Released in November 1995, the images are providing astronomers with new insights into how stars are born.

The size of the star is determined by its gravity, which causes it to contract and by fusion, which causes it to expand. A young star initially shines a blue-white light. A young star then, is a BLUE-WHITE STAR.

Blue-White Star

As it gets older, it changes into a YELLOW STAR or a YELLOW DWARF like our Sun because of its size relative to other stars.

The Sun, a yellow dwarf star (Artist’s 3D illustration)

Further cooling changes a yellow star into a yellow star into a RED STAR. By this red phase, the star would have expanded until the elements that fuel its nuclear reactions are used up.

Red Giant Star

The star would then collapse from the inward force of its own gravity becoming a WHITE DWARF.

White Dwarf Star

With no source of energy, the star eventually becomes cooler and dimmer, “dying” as a BLACK DWARF.

Sometimes, a dim star may suddenly flare up and become a much brighter star. This causes the star to become a NOVA. Massive stars may cause a bigger explosion. The exploding star is called a SUPERNOVA. It may cause interference to our own communication systems.

Supernova (photo courtesy of NASA)

A massive star has a gravity so strong that its radiation are bent back to itself and cannot escape f a star is called a BLACK HOLE

Artistic visualization of a black hole (picture courtesy of NASA)

PROTOSTAR

BLUE-WHITE STAR

YELLOW DWARF

RED GIANT

RED SUPERGIANT

WHITE DWARF

BLACK DWARF

NOVA

SUPERNOVABLACK HOLE

Birth & Death

of a Star

Characteristics of a Star

COLOR AND TEMPERATURE A star’s color reveals its temperature.

Stars first glow red-hot, then yellow hot then blue-hot and finally white hot as their temperature increases. Thus, the color of the star indicates its temperature

Table 1: Color and Temperature of Selected Stars

Star Color Surface Temperatur

e in Celcius

Sun Yellow 5,700

Proxima Centauri

Red 2,300

Epsilon Iridani

Orange 4,600

Vega White 9,900

Sirius White 10,000

Ainilam Blue 27,000

What is your

observation?What is

your

inference about

the stars’

temperature

and color?

“The temperature of a star determines its color.”

BRIGTHNESS

The brightness of a star as seen from the Earth depends on two factors, distance and actual brightness (or absolute brightness). The star’s brightness as seen from Earth is its APPARENT BRIGHTNESS, which depends on how far away a star is from Earth. Astronomers consider the star’s absolute brightness when comparing stars. A star’s absolute brightness is the brightness a star would have if all stars were the same standard reference from Earth.

MASS The mass of a star can be determined

only by the gravitational effects of one star on another. Since about half of all stars are found in systems were two or more stars that orbit one another, astronomers were able to estimate masses of many hundreds of stars. The most luminous stars are typically the most massive.

Suggested Videos

The Universe: Life and Death of a Star (this video shows visualization on the formation of stars)

http://youtu.be/NuXPAQOLato

The Sun (a documentary about the Earth’s nearest star, this video will help students to fully understand the behavior and characteristics of stars by comparing it with the Sun)

http://youtu.be/C2FETG7tCF0

QUIZ: EXPLANING/ IDENTIFYING

1. Like all stars, our Sun will die too. If this happen, what do you think will happen to the planets and other heavenly bodies in our system?

2. Describe the life and death of stars. You can use illustration, a diagram or an essay to help you explain your answer.

3. The star Algol is estimated to be as bright as the star Aldebaran and have approximately the same temperature as the star Rigel. Using your understanding on the characteristics of stars, give at least two conclusions that you can formulate on the characteristics of these three stars.