STARS Chapter 8 Section 1

What we will talk about today What color tells us about the temperature of a star How we can identify what a star is made of How a star’s brightness, location, and distance from earth are measured

How are Stars Classified? They are classified by their temperature (color) and brightness. The H R Diagram shows the temperature and brightness of stars.

What are stars? Stars are huge, bright balls of burning gas. Stars are different colors because of their temperatures, and scientists can tell how much heat a star gives off by studying its color. Who has used a telescope?

Bunsen Burner vs. Candle What flame is hotter? The flame of the Bunsen burner or the candle?

Colors of Stars A blue flame is much hotter than a yellow one. Stars are similar: blue stars burn hotter than yellow ones. Red stars are coolest. This is Betelguese, a Red Giant Star What color is our sun?

What temperatures are these stars?

What are stars made of? Stars are made of gas. Hydrogen(H) and helium(He) are the two main elements that make up a star. What is an element? Stars also contain small amounts of other elements, such as carbon, nitrogen, and oxygen. Each star is made up of a different mix. To find out what a star is made of scientists study the light from the stars.

What is light? Light is actually made up of many colors. These colors are called the spectrum. Many colors make up a spectrum, including **red, orange, yellow, green, blue, indigo, and violet. ROY G BIV will help you remember the spectrum. Where else have you seen these colors?

A star is made up of different elements in the form of gases A star is made up of different elements in the form of gases. The inner layers are very dense and hot. But the outer layers are made up of cool gases. Elements in a star’s atmosphere absorb some of the light that radiates from the star. Because different elements absorb different wavelengths of light, astronomers can tell what elements a star is made of from the light they observe from the star. This is called the spectrum.

Why do Scientists Study Light? Scientists are able look at light through a machine called a spectrograph to break up a star’s light into a spectrum. Each element has a particular pattern of lines that appear in an emission spectrum. The emission spectrum shows scientists what elements are in the star. What can studying a star’s spectrum tell an astronomer?

Distances To The Stars Stars are separated by vast distances. Astronomers use units called light years to measure the distance of stars A light-year is the distance that light travels in a vacuum in a year Proxima Centauri, is the closest star to the sun. 9,461,000,000,000 trillion km or 5,878,000,000,000 trillon miles. 

Another way to describe stars: Magnitude or Brightness Scientists give each star a number to show its brightness, or magnitude. The dimmest stars have the largest magnitude numbers. The brightest stars have the smallest magnitude numbers.

What is the brightest star?

Quick Vocabulary Review What does apparent mean? 1)Clearly understood 2)Seeming real or true, but not necessarily so. What does absolute mean? complete What does actual mean? Existing in fact

One type of magnitude The brightness(or magnitude) of a star as we see it from Earth is the star’s apparent magnitude.*** A bright star can look very dim if it is very far away from Earth. A dim star can appear bright if it is closer to Earth. Where would you see the apparent magnitude of a star?

Absolute Magnitude A star’s absolute magnitude is the actual brightness of the star. Astronomers use a star’s apparent magnitude and its distance from earth to calculate its absolute magnitude.**** What can we tell about these stars magnitudes?

Measuring the distances of stars with parallax**** Parallax is the object’s apparent shift in motion when viewed from different locations. It is an optical effect. Astronomers can measure parallax and use it to calculate exact distances to stars. Does the man on the right(V2) see the moon as closer or farther away than the man on the left? Where would someone use parallax?

Brightness of a Star. Absolute magnitude – how bright a star really is. Apparent magnitude – how bright a star looks from Earth.

What do scientists use to calculate distance to stars? Because stars are so far away, astronomers use light years to measure the distance from Earth to the stars. A light year is the distance that light travels in one year, or 186,282 miles per second, or 5.88 trillion miles**** This quasar is 10 billion light years from Earth

Motion of the Stars As we stand on Earth and look at the stars, they seem to move. This is because the Earth revolves around the sun and we are on the surface of the Earth as it revolves. This is called stars’ Apparent Motion. What has moved? Based on what you Now know about Apparent Motion, What would Actual Motion be????

Motion of stars.

Classifying Stars H-R Diagram The H-R Diagram (Hertzprung-Russell diagram) is a graph that shows the relationship between a star’s surface temperature and its absolute magnitude. Reading the H-R Diagram The diagonal pattern on the H-R diagram where most stars lie, is called the main sequence. Where is our sun?

The HR

To sum it all up……. Why do some stars look different than others? When we look at a star from Earth, will it look the same in 6 months? Why?