1. Measuring Stars

2. Visible Spectrum & Wavelengths

3. Spectral Types Continuous spectrum: Produced when white light passes through a prism Emission spectra: Produced from a heated gas giving off light Absorption spectra: Produced when white light passes through a cool gas

4. Spectra & Star Composition Can tell a star’s composition by looking at its spectra (usually an absorption spectra) We can identify the spectra of various elements Comparing a stars absorption spectra to the elements can indicate composition

5. Spectra & Star Composition

6. Spectral Lines of a Star

7. Dopplar/Wavelength Shifts In space there is no up down left or right, only towards or away Motion towards & away causes the light given off to be squeezed or stretched Blue-shift: wavelengths from objects moving toward another get squeezed Red-shift: wavelengths from objects moving away get stretched

8. Wavelength Shifts

9. Groups of Stars & Judging Distance in Space

10. Constellations Stars named after animals, mythical characters, & everyday objects 1.88 constellations named by ancient people 2.Circumpolar stars: can be seen all year long depending on the hemisphere you live Stars may not actually be close to each other in space

11. Constellations Cygnus The Swan Ursa Major (Big Dipper)

12. Star Clusters & Binaries Clusters: Stars actually close to each other & held close by their gravity –Open clusters: stars NOT densely packed –Globular Cluster: stars ARE densely packed Binaries: Stars that come in pairs orbiting a center of mass (over ½ of all stars) Pleiades Cluster Arches Cluster Binary System

13. Judging Distances: Parallax Parallax: apparent change in a star’s position compared to background stars More apparent change = closer the star is

14. Units of Distance Astronomical Unit (AU): average distance from Sun to Earth (93 million miles) Light Year (ly): distance light travels in one year (~9.5 trillion km, or 5.9 trillion mi) Parsec (pc): it is equal to 3.26 ly

15. Basic Properties of Stars Magnitude: general brightness of a star –Ranked using + & - numbers –A +1 is 100x’s brighter than a +6 –Brightest stars have negative magnitude numbers Apparent Magnitude: brightness as it appears from Earth Absolute Magnitude: brightness of a star from 10 parsecs Luminosity: amount of energy output from the surface (very similar to brightness)

16. Magnitude Comparison