Presentation is loading. Please wait.

Presentation is loading. Please wait.

Agenda Review magnitude scale and HR diagrams Another way to measure distance: Spectroscopic Parallax Please pick up essays after class.

Similar presentations


Presentation on theme: "Agenda Review magnitude scale and HR diagrams Another way to measure distance: Spectroscopic Parallax Please pick up essays after class."— Presentation transcript:

1

2 Agenda Review magnitude scale and HR diagrams Another way to measure distance: Spectroscopic Parallax Please pick up essays after class

3 Apparent Magnitude scale Sun Naked eye Polaris Faintest object With binoculars Venus Sirius Full moon Faintest object 4 m telescope

4 Absolute magnitude Luminosity = how much light a star is giving off  (like wattage for light bulbs)  Compared to the Sun (Lsun) Absolute magnitude = how bright (what magnitude) a star would appear at 10 parsecs (32.6 light years)

5 Standard Candles A. –26 B. –23 C D. –33 E. Cannot determine The Sun has an apparent magnitude of –26. What might its absolute magnitude be?

6 Recall from last time… We know temperature  O B A F G K M We can determine luminosity (if we know distance) Temperature and luminosity are related!  main sequence

7 The HR Diagram!! O B A F G K M Spectral Class HOTCOOL Bright Dim Sun Main Sequence Stars White Dwarf Stars Red Giant Stars Absolute magnitude

8 Given two stars, which one looks brighter in the night sky? A. Star A B. Star B C. Look the same D. Cannot conclude Spectral Class O B A F G K M A B Absolute magnitude

9 Given two stars, which is larger (more surface area)? A. Star A B. Star B C. Look the same D. Cannot conclude Spectral Class O B A F G K M A B Absolute magnitude

10 Spectroscopic “parallax” Another way to measure distance It’s not parallax! How does it work? 1. Measure star’s spectral type 2. Get luminosity (absolute magnitude) from spectral type (how?)* 3. Use the “standard candle” method to get distance.

11 *Temperature => Luminosity O B A F G K M Spectral Class HOTCOOL Bright Dim Sun Main Sequence Stars White Dwarf Stars Red Giant Stars Absolute magnitude Works only for main sequence! Spectral type Luminosity

12 Summary We can measure apparent magnitude and spectral type. The main sequence lets us infer absolute magnitude from spectral type. Comparing apparent magnitude to absolute magnitude gives us distance.

13 Something to ponder... Astronomy, as an observational science, has limitations:  Can’t build stars in our laboratory  Can only observe what happens to be available  Can’t go back in time to watch stars form, or go forward in time to see them die. How, then, can we learn about the life cycles of stars? Sample stars that exist now in various stages of development.

14 Next time Star Clusters — and how they hint at Stellar Life Cycles

15 Activity #7 Spectroscopic Parallax


Download ppt "Agenda Review magnitude scale and HR diagrams Another way to measure distance: Spectroscopic Parallax Please pick up essays after class."

Similar presentations


Ads by Google