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The Cosmos. " We are a way for the Cosmos to know itself." Carl Sagan. Star Light, Star Bright. Stars and their Characteristics Life Cycles of Stars Photos. Video comparison. Stars differ from one another in. Mass Age Composition Brightness Size Surface temperature Distance from Earth.
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The Cosmos "We are a way for the Cosmos to know itself."Carl Sagan
Star Light, Star Bright Stars and their Characteristics Life Cycles of Stars Photos
Stars differ from one another in • Mass • Age • Composition • Brightness • Size • Surface temperature • Distance from Earth
Our star is The Sun A star makes fuel by combining atoms in a process called…
The Sun is 93,000,000 miles away. • How long does it take for light to reach us from the sun? • A) 93,000,000 years • B) 8 minutes • C) Practically no time at all
It takes about 8 minutes. • The next closest star is Proxima Centauri. • It takes 4 years for light from this star to reach us. • So how far away is this star?
4 light years • Light Year • The distance light travels in one year • So a light year is a unit for very, very, very large distances.
Ancient peoples looked at the stars at night for entertainment. “No stars for you until you clean your slate!”
Anyway, people have been observing stars for a long time. • They named the star patterns or clusters according to mythic heroes. • These clusters of stars that appear to be close together because they are so far away and that resemble these figures are called constellations.
More about constellations • There are 88 that can be seen from Earth. • These patterns are not altered for thousands of years and the change would be very gradual to us. • Some constellations can be seen all year long and some cannot.
Ursa Major • The Big Dipper • Also known as the Great Bear • The two stars farthest from the “handle” are pointer stars. They point toward the North Star (Polaris).
Do stars move? During the day During the year
Circumpolar • Describes stars and constellations that are visible to us in the northern hemisphere all year long. • Will Polaris always be the North Star?
Ursa Minor (Little Bear) is the Little Dipper. • This is an important constellation because it contains the North Star or Polaris. • Polaris gets its name based on the fact that it is over the North Pole. • The Earth rotates from west to east so Polaris stays in roughly a fixed part of the sky.
Some constellations can only be seen during certain seasons. • ORION • Orion is called the Hunter. • We only see Orion in the winter.
Lyra is only seen in the summer and fall night sky. • Lyra is the harp of the Greek musician Orpheus. • Lyra contains the 5th brightest star in the sky (Vega).
Stars have different amounts of brightness. • Apparent Magnitude • Ptolemy is credited with the first extensive system of putting a brightness value with stars • If a star appears really bright like the Sun, we say is has a high apparent magnitude.
Ptolemy – “One mochachino double carmel vanilla latte, please.”
“So is a star with a bright apparent magnitude really that bright?”
All stars have an amount of luminosity (actual brightness). • This depends on a star’s • Size (bigger is brighter) • Temperature (hotter is brighter)
Absolute Magnitude • This is the measure of how bright the star would be if all stars were at the same distance • If a star actually is really bright, no matter how far away it is, then we say it has a high absolute magnitude.
Stars vary more in size (volume) than they do in mass. • A star’s mass cannot be directly measured. • How do astronomers get an idea of how massive a star might be? • Gravity. A more massive star will have a greater gravitational pull.
So to wrap up • Stars can differ in • Temperature • Size • Mass • Density • Luminosity • Composition
H-R D I A G R A M
What would our Sun be?Hot or ColdBright or Dim? Our sun is a Main Sequence Star
Red Giant Red Giant
Supergiant (Betelgeuse)
