Twinkle twinkle little star, how I wonder what you are! Do you wonder what a star is? Do stars really twinkle? Let’s find out all about stars in this lesson.
What Is a Star?
A star is a huge glowing ball of hot gases that are held together by gravity. The two main gases that make up a star are hydrogen and helium.
Life of a Star
Stars are born because of a natural pulling force called gravity. The life of a star goes through 7 stages:
1. Gas Cloud
There are very large and fluffy clouds of gas and dust scattered throughout the universe called nebulae. The power of gravity makes clumps inside these fluffy clouds. Then, the clumps start to get tightly compacted together and to get denser. They also get hotter and hotter in the centre.
When the centre of a clump becomes very hot, the atoms of the hydrogen gas come together to form helium. This process is called “Nuclear Fusion”. The nuclear fusion releases high amounts of energy, which creates a protostar. A protostar is a new baby star and it grows into a star through its life cycle.
3. Newborn Star
The young star begins to produce strong winds that push away the surrounding gas and molecules. Then, the star becomes visible for its first time.
4. Main Sequence Star
When the gas pressure in the star’s core becomes as powerful as the gravity, the star reaches a state of balance. This gives the star a solid shape, and it becomes a main sequence star. During this stage, the star shines steadily using the burning hydrogen as a fuel. Stars spend 90 percent of their life cycles in this stage.
5. Red Giant
After a while, the hydrogen fuel in the star’s core runs out causing the star to lose its balance. As a result, it expands and becomes a red giant. The surface of a red giant is cooler than that of a main sequence star. Some massive stars become supergiant.
6. Other Elements’ Fusion
As the star expands, it begins fusing helium in its core to produce energy. This energy prevents the core from collapsing. When the helium runs out, the core shrinks and begins to fuse carbon. After a while, the iron appears in the core. The iron fusion absorbs energy, so it causes the core to collapse.
7. Planetary Nebula and White Dwarf
Eventually, the star explodes, and most of its material is blown into space. As the star’s outer layers and ejected matter disperse, they form a shell around the dying star’s dense core; this is known as a planetary nebula. Less massive stars do not explode like this, however. Instead, the cores shrink into small, hot stars called white dwarfs, and the other material drifts away. White dwarfs will continue to glow faintly because of the remaining heat from earlier stages in its life cycle.
What Happens to a Star When It Dies?
A star never really dies, but it goes through a process like reincarnation. The remaining material sticks around and creates other formations in space. Astronomers are not yet certain about what eventually happens to stars because the Earth’s universe is still very young.
What Does a Star Look Like?
Stars vary in brightness, size, temperature, color and mass.
- There are two characteristics that define a star’s brightness: luminosity and magnitude. Luminosity is determined by size and temperature. Apparent magnitude of a star is the brightness that can be visible to us, while absolute magnitude is the star’s true brightness. So, some stars appear brighter to Earthlings simply because they are closer.
- Astronomers measure the temperature of a star on a scale called the Kelvin scale. The coolest stars are about 2,500 K, while the hottest stars can reach 50,000 K.
- The colour of a star is determined by its temperature. The hottest stars are blue, while red stars are the coolest. Medium stars are mostly white or yellow. Sometimes stars bend colours, such as red-orange or blue-white stars.
- A star’s size determines its brightness. A far star might appear bright from Earth if it is huge.
- Stars can vary greatly in density. While two stars may have the same size, they may not necessarily have the same mass.
Types of Stars
Stars can be classified as O, B, A, F, G, K, and M-type stars. M-type stars are the coldest, while O-type stars are the hottest. In addition, M-type stars are quite common, while O-type stars are rare.
- O-type stars: The hottest stars. Their colour is blue. They are more than a million times brighter than the Sun.
- B-type stars: Their colour is blue. They are hundreds to thousands of times brighter than the Sun.
- A-type stars: Their colour is blue. They are tens of times brighter than the Sun.
- F-type stars: Their colour is blue to white. They are brighter than the Sun.
- G-type stars: Their colour is white to yellow. They are bright like the Sun.
- K-type stars: Their colour is orange to red. They are faint.
- M-type stars: They are the coldest stars. Their colour is red. They are faint.
Why Are Stars Important?
Stars have always been important. They played a part in religious ceremonies. Navigators also used the stars to travel at night, both over land and at sea. Early astronomers used the stars to track the movement of the Sun and the planets. The motions of the stars over the course of a full year also helped them build the first accurate calendars, to know when to plant fields and when to harvest.
10 Interesting Facts About Stars
- You can see about 7,000 stars with the naked eye from Earth, but there are actually so many stars in the universe that it is impossible to count them all.
- Our Sun is a star. It is around 4.5 billion years old, and it is in the middle of its life. It is a yellow star, and its temperature is medium.
- Most of the stars you see in the night sky are bigger and brighter than the Sun.
- Most of the stars in the universe are red dwarfs.
- Stars are very far away. The Sun is the closest star to Earth, but it is still located 4.24 light years away. The fastest spacecraft would take 70,000 years to reach the Sun.
- Average stars are between 1 and 10 billion years old, but some stars are older than this.
- The bigger the star is, the shorter it lives. This is because large stars burn through their fuel much faster.
- Giant stars explode into a bright supernova when they die. A supernova explosion is one of the brightest events in the universe.
- Looking at stars is looking back in time. It takes millions of years for a star’s light to reach our eyes, which means that we are seeing stars from long ago. In fact, many stars that are visible no longer exist.
- Stars do not actually twinkle. As the light of a star travels to us, the Earth’s atmosphere disrupts the light’s path making the star appear as if it is twinkling. In addition, the air moves constantly making the starlight appear to be shifting and shimmering.
What Are Constellations?
A constellation is a group of stars in the night sky that form a picture or a pattern when viewed from Earth. This pattern may take the shape of an animal, an object, a mythological creature, a man, or a woman.
How Many Constellations Are There?
There are 88 major star constellations in the sky. Not all constellations can be seen at once, and some are nearly impossible to be seen without a telescope. Your location on Earth determines which constellations you will be able to see. Some of them can only be seen in the skies of the Northern Hemisphere, while others are seen in the Southern Hemisphere.
10 Interesting Facts About Constellations
- Constellations always travel from the east to the west.
- The Sun is the only star in our galaxy, the Milky Way, that does not belong to a constellation.
- The most recognizable constellation is Orion. It is located in a place that makes it visible from many locations around the world.
- The largest constellation in the night sky is the Hydra, and it covers 3.16% of the sky.
- The smallest constellation in the night sky is Crus, and it covers 0.17% of the sky.
- The brightest constellation in the night sky is Crux.
- Some constellations have families. A constellation family is a group of constellations located within the same region of the night sky. A constellation family often takes its name from its most important constellation.
- In ancient times, constellations were used as part of the calendars. People used them to know when they had to plant or harvest crops and when winter was coming.
- Farmers have used constellations in their daily lives since ancient times. They used them to keep track of the seasons.
- Constellations can be used for navigation. For example, the Ursa constellation can help you find the North Star (Polaris).
What Are Galaxies?
A galaxy is a group of stars, clouds of gas, and dust particles that are held together by gravity, and they move together through the universe. Galaxies were formed billions of years ago after the universe began. Our Earth and the entire solar system is a part of the Milky Way Galaxy.
Types of Galaxies
Galaxies are divided into three main types based on their shapes: elliptical, spiral, and irregular.
- An elliptical galaxy may sometimes be round and other times oval, or stretched out. It has more stars near its center and fewer stars in its outer areas. It has a smooth light distribution, and it appears as ellipses in photos.
- A spiral galaxy looks like a pinwheel. It has a central disk with two or more curved arms winding outward. Older stars are usually in the disk, while younger ones are in the arms. The arms contain much dust and gas, which helps new stars form. The Milky Way is a spiral galaxy.
- Irregular galaxies are those that are not elliptical or spiral, and they are shaped unusually. They are usually small and very chaotic, and many of them have no obvious center point. Some of them are formed because of a crash between several galaxies. Irregular galaxies are not very common.
8 Interesting Facts About Galaxies
- The word galaxy is derived from the Greek word “galaxias” which means “milky,” which is the reason why our galaxy is called the Milky Way galaxy.
- Astronomers believe that there are over 100 billion galaxies in the observable universe.
- Most of the observed galaxies so far (two-thirds of them) are spiral galaxies.
- The diameter of most galaxies is between 1,000 and 10,000 parsecs. A parsec equals approximately 31 trillion kilometres.
- Most galaxies in the universe are dwarf galaxies, meaning that they are small compared to other galaxies.
- Small dwarf galaxies can have ten million stars, while large galaxies can have hundreds of trillions of stars.
- Almost all large galaxies contain a black hole at their centers. The power of the gravity of that black hole helps hold the galaxy together.
- A spiral galaxy called the Andromeda will one day collide and merge with our galaxy, the Milky Way.