What We Know About What We Know About Stars So FarStars So Far

There are many There are many different types of light different types of light energy…………………energy…………………

Some energy we can see – Visible light

RedOrangeYellowGreenBlueIndigoViolet (purple)

There are many There are many different types of light different types of light energy…………………energy…………………

Some energy we cannot see – Infrared and Ultraviolet Light

These energies differ These energies differ based on their based on their wavelengthwavelength

•Red light has a larger wavelength than violet•Red is less energetic than violet•Violet has a smaller wavelength than red light and is a more energetic wavelength of light than visible light.

•Ultraviolet has a shorter wavelength and a higher frequency

Stars release many types Stars release many types of energy that are part of of energy that are part of the electromagnetic the electromagnetic spectrum.spectrum.This is what makes

all stars similar (they release energy during nuclear fusion).

Scientists use different energies within the spectrum to examine celestial objects (objects located in outer space).

Scientists use different energies Scientists use different energies within the spectrum to examine within the spectrum to examine celestial objects (objects celestial objects (objects located in outer space).located in outer space).

Visible light – tells us about the temperature of a star.Red = Cooler temperatureBlue = Hotter temperature

Scientists use different energies Scientists use different energies within the spectrum to examine within the spectrum to examine celestial objects (objects celestial objects (objects located in outer space).located in outer space).

Radio waves – help us to create images of distant objects that cannot be seen.

Scientists use different energies Scientists use different energies within the spectrum to examine within the spectrum to examine celestial objects (objects celestial objects (objects located in outer space).located in outer space).

X-ray Radiation – helps us detect supernova explosions and black holes.

What We See When What We See When We Look at the SkyWe Look at the Sky

Stars can be organized into Stars can be organized into different categories based on different categories based on

their apparent brightness.their apparent brightness. •Scientists used to use a simple scale of brightness to classify stars.The star’s brightness was dependent on how close it is to the Earth. The closer a star is to the Earth, the brighter it would appear.They used a scale of 1 – 61 = brightest stars6 = least bright stars

Sizes of Different StarsSizes of Different Stars

Stars can be organized into Stars can be organized into different categories based on different categories based on

their apparent brightness.their apparent brightness. •Scientists also figured out that the color of the star told us something about their temperature •Red-colored stars are cooler in temperature compared to blue-colored stars.

Stars can be organized into Stars can be organized into different categories based on different categories based on

their apparent brightness.their apparent brightness.

Scientists later came up with a more precise system for measuring brightness.

Sirius A = Brightest star in night sky is -1.4

Sun = -27

Stars can also be organized into Stars can also be organized into different categories based on different categories based on their absolute brightness.their absolute brightness.

Scientists measure the luminosity of the star.This is the total amount of radiation a star emits (the visible and invisible wavelengths of energy).This system is not dependent on how far away a star is from the earth.

Stars can also be organized into Stars can also be organized into different categories based on different categories based on their absolute brightness.their absolute brightness.

Scientists (Hertzprung and Russell (HR)) found that luminosity is dependent on the surface temperature of the star.When you plot stars on a graph using this system (comparing surface temperature and luminosity), you will find that the stars fall into groups.

Stars can also be organized into Stars can also be organized into different categories based on different categories based on their absolute brightness.their absolute brightness.

We can use this information about a stars luminosity to help determine where a star is in its life cycle.

Stars move through a set life Stars move through a set life

cycle.cycle.

At the beginning of their lives, stars are main sequence starsThese stars begin as a swirling cloud of matter (H and He mostly) that eventually reaches temperatures of 15 million Kelvins and at this point fusion begins (atoms colliding to form heavier elements – H colliding to form He).

Stars move through a set life Stars move through a set life

cycle.cycle.

•The red giants produce heavier elements like Oxygen and Nitrogen during fusion•The very heaviest elements form when a supernova explodes.

Stars move through a set life Stars move through a set life

cycle.cycle.

As the stars age, they use up their energy and lose mass.•Smaller, cooler stars burn their fuel slowly and last longer•Massive, supergiant stars burn their fuel quickly and don’t last as long.The loss of mass in a star creates a stellar wind (called solar wind in the case of our Sun).

Stars move through a set life Stars move through a set life

cycle.cycle.

Eventually, some stars lose so much mass that they shrink down and become a nebula (a shell of what they once were).

Stars move through a set life Stars move through a set life

cycle.cycle. In other cases, stars will explode and become a neutron star or a black hole.

When these stars die, heavy elements are formed as matter combines.

Stars move through a set life Stars move through a set life

cycle.cycle.

Eventually, the matter that was used to make up a star will contract to form new stars and the process of a star’s lifecycle will begin again.