Stars and Star Patterns Revised by Tracy Sikes

Stars and Star Patterns Revised by Tracy Sikes

What is a star? A star is a huge ball of very hot gases like hydrogen and helium.

Our sun is the closest star to our planet.

Stars give off light and heat energy.

Facts about the sun: • The center of our solar system. • Sometimes has dark spots called sun spots which do not give off as much heat or light. • Red streams and loops are called solar flares. • Both last only a few days.

Scientist classify stars in several ways: • By color • By brightness • By size

Star Colors: color tells the temperature • • Red (coolest) Yellow White Blue (hottest)

Star Brightness depends on two things: • How far it is from Earth. • How bright it actually is.

Star Sizes • Stars come in different sizes. • Some stars are even smaller than Earth. • The smallest stars are called neutron stars.

What is our Sun? • • A yellow star Medium size Medium brightness Medium heat

Stars go through stages: First Stage: • • Stars form as clouds of swirling dust. Gravity squeezes the cloud. It circles faster and faster. The cloud is called a nebula or a stellar nursery. • A star is born!

What happens next? • Small stars grow to a Red Giant. • This star will die and become a White Dwarf.

What about other stars? • Big stars explode and are called Super Novas. • Some Super Giant stars explode and make a black hole. • Nothing can escape a black hole’s suction because of gravity.

What about our Sun? Our sun will grow to be a Red Giant and then a White Dwarf.

A pattern or group of stars in the sky is called a constellation. There are 88 constellations in all. People of ancient time saw the constellations as characters or animals in the sky. They made up stories to explain how the object, animal, or character came into the night sky.

Orion is one of the brightest constellations and is a mythological character. According to Greek myths, Orion was a hunter who used to brag all the time. This bothered the gods. When the gods were tired of him, they sent a scorpion to bite and kill him. The gods felt bad for having Orion killed. They placed him in the sky.

Stars as Tools for Navigation v Earth rotates on its axis. This makes most constellations appear to rise in the east and set in the west during the night. v Most constellations appear in many different positions in the sky as the Earth revolves around the sun. v There is a group of stars that appear in the sky all night long and all year long. It seems that these stars do not rise and set, but circle the Earth’s north pole each night. These stars are called circumpolar.

Stars as Tools for Navigation v The North Star is called Polaris and located directly above the North Pole. This star appears in the same place every night all year long. v In the Northern Hemisphere, if you find Polaris you will be able to tell which direction is north. v. The Southern Hemisphere does not have a star to help you find its pole. Instead it has what is known as the Southern Cross. v The Southern Cross consists of 4 bright stars and some dimmer ones. All of these together point to the south pole.

What is the Zodiac? • A group of 12 constellations. • Lined up one after another all around the sky. • Each month a different member of the Zodiac rises in the east. • Each day more of it becomes visible.

Stars As Calendars Ø It seems that the constellations in the east rise a little earlier each evening. This means that the seasons are changing and we are seeing different constellations. Ø An example is in the Northern Hemisphere, Orion is high in the sky during the winter and Scorpio can only be seen during the summer. Ø People of ancient times used these seasonal changes in the stars as calendars. Ø It is believed that the ancient people used the constellations to tell them when to plant and harvest crops. An example would be Leo and Virgo in the night sky would signify that the last frosts of the year have happened and it is safe to plant. This worked much like our paper calendars work for us today.

What is a galaxy? • Have you seen a bright band of stars on a clear summer night? • That’s the Milky Way Galaxy. • A galaxy is a huge system of gasses, dust, and stars. Billions of stars! • Our Sun is on the edge of the Milky Way Galaxy.

Are there different kinds of galaxies? Galaxies are generally classified by their shapes: • Spiral galaxy- The Milky Way is spiral • Elliptical galaxy • Irregular

What is the Universe? • The universe is everything that exists in space! • There are millions of galaxies in the universe.

• The brightest constellation is Crux (the Southern Cross). • The constellation with the greatest number of visible stars in it is Centaurus (the Centaur - with 101 stars). • The largest constellation is Hydra (The Water Snake) which extends over 3. 158% of the sky.

1. What is a constellation? 2. Why is Polaris called the North Star? 3. How did ancient people use the seasonal appearance of certain constellations? 4. Name two constellations.

More Review Questions • • • How many galaxies are there? How do scientists classify stars? What is the name of our galaxy? What type of galaxy is it? Describe our star, the sun.