Ch. 15-1 Stars Chapter 19, Section 1 Part 1

Stars Stars are huge, hot, brilliant spheres of gas. To learn about stars, scientists study starlight.

Color of Stars Look at the candle and Bunsen burner. Which is hotter? The blue flame of the Bunsen burner is much hotter than the yellow flame of the candle. Stars are different colors too, so we know they are different temperatures.

Composition of Stars The rainbow of colors produced when white light passes through a prism is the spectrum. A spectrograph is used to spread starlight out into its colors.

Making an ID Absorption spectra show what elements are in a star’s atmosphere. For example, this spectrum shows the presence of hydrogen.

Absorption Spectrum of the Sun Our sun shows absorption lines for hydrogen (marked with an H) and other heavier elements.

Ch. 15-1 Stars Chapter 19, Section 1 Part 2

Classifying Stars Stars are classified by how hot they are. Different surface temperatures result in different colors.

Brightness of Stars The lower the magnitude = the brighter the star. (Sun = -26.8) Magnitude means size, or in this case brightness.

2 Ways To Look At Brightness Apparent Magnitude – How bright the star really looks from Earth. The farther away from us, the dimmer the star looks. Absolute Magnitude – How bright the star really is. If all stars were the same distance from us, how bright would it look compared to the other stars.

Ch. 15-1 Stars Chapter 19, Section 1 Part 3

Distance To The Stars A light-year is the distance light will travel in one year or: 6,000,000,000,000 miles! The nearest star to our sun is 4.3 light-years away. Some stars are billions of light-years away.

Parallax Stars near the Earth appear to move more than distant stars. This apparent shift in position is called parallax.

Motions of Stars Because of the earth’s tilt and revolution around the sun, we see different parts of the sky at night. We see different constellations at different times of the year.

Motion of Stars (con’t) Because of the earth’s rotation, the stars all seem to circle Polaris (the north star) once every 24 hours.

Motion of Stars (con’t) Even though the stars are moving in space, they are so far away the constellations look the same to us now as they did to the Greeks who named them thousands of years ago.

Review Is a yellow star hotter or cooler than an orange star? Suppose you see two stars of the same apparent magnitude. If one star is actually four times as far away as the other, how much brighter would the farther star really be?