TOPIC #4 BEYOND OUR SOLAR SYSTEM

Section #1: Properties of Stars

THE NIGHT SKY Stars in the night sky display many characteristics and

patterns.

Noticeable patterns seen among stars are called constellations and they are used to designate regions of the sky.

Stars in the region of a constellation are considered part of the constellation…even if they are not a part of the pattern.

There are 88 constellations.

CHARACTERISTICS OF STARS Stars are the large balls of gas that

give off electromagnetic radiation…just like our sun which is a star.

Understanding star characteristics gives us an understanding of the universe.

STAR COLOR AND TEMPERATURE The amount of energy given off by a

star is determined by its temperature.

We can’t measure the temperature of stars millions of light years away but we can use their color to identify temperature.

BINARY STARS AND STELLAR MASS More then half of the stars in the

universe orbit another star and they are called binary stars.

Gravity causes them to orbit each other and an objects gravity can be used to identify its mass.

With knowing a stars orbit and gravitational attraction scientists can guess the stars mass.

MEASURING DISTANCE TO STARS The motion of stars is hard to

determine because the earth is constantly moving.

In fact the Earth has moved 18,641.15 miles in the amount of time it took us to read this sentence.

MEASURING DISTANCE TO STARS The motion of the Earth causes a shift in the

apparent position of a star called parallax.

The closer a star the greater the parallax.

Scientists take a picture of a star and then take another 6 months later and they find the middle of the two different parallax angles and can say that that is the actual location of a star.

MEASURING DISTANCES TO STARS Stars are so far away that their

distance isn’t measured in miles it is measured in light years.

A light year is the distance light can travel in 1 year.

This unit is based on the constant speed of light and is roughly 9.5 trillion kilometers.

STELLAR BRIGHTNESS A stars brightness is called its

magnitude.

A stars brightness as it appears from Earth is its apparent magnitude.

This is determined by a stars size, its heat and its distance from earth.

STELLAR BRIGHTNESS The actual brightness of a star is called

its absolute magnitude.

The factors that determine a stars apparent magnitude can make two stars with the same absolute magnitude look like they have different brightnesses.

HERTZSPRUNG-RUSSELL DIAGRAM A Hertzsprung-Russell Daigram shows the

relationship between a stars absolute magnitude and its temperature.

90% of stars fall into the region of the diagram in the upper left called the main sequence.

Red giants and Supergiants are extremely large and bright stars found in the upper right hand corner of the diagram.

STAR LIFE CHANGES A star is born in a cloud of gas and dust

called a nebulae.

As some stars age they increase and decrease their brightness and this change in brightness is due to explosion of energy called a nova.