1 / 18

Finding Distances to Stars with Stellar Parallax and Inverse-Square Law

Learn how astronomers use geometry to measure distances to stars through stellar parallax and the inverse-square law. Understand the relationship between flux, distance, and luminosity. Discover how to calculate the wattage and brightness of stars.

sbrad
Download Presentation

Finding Distances to Stars with Stellar Parallax and Inverse-Square Law

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Stars

  2. Distance

  3. Find d Getting distances to stars: • Geometry: ‘Stellar Parallax’ • > Only direct method! • 2. Inverse-Square Law * Measure F * Know (or guess!) L

  4. Stellar Parallax Triangulation: d p x q Baseline x and q (or x and p)  d

  5. p x d Earth For getting distances to stars, we want longest possible baseline: p  parallax angle d  distance x = 1 AU; measure p  d

  6. p d As a practical matter, how do we get p? B A Star appears to shift position against background – the parallax effect. Shift proportional to 2  p A B

  7. Clearly, as d increases, p decreases. Astronomers find: p: arcseconds (1 arcsec = 1/3600o) If p = 1 arcsec, 1 parsec = 3.26 light year = 206,265 AU

  8. Nearest star: Proxima Centauri p = 0.772 arcsec d = 1.295 pc = 4.22 ly

  9. Inverse-Square Law Luminosity: total amount of energy radiated per second (“wattage”) Watt? Watt? 50 W 100 W Twice the luminosity

  10. These stars would appear to be about equally “bright.” Does this mean they’re equally luminous?

  11. (Apparent) Brightness  Luminosity 2 stars – differ in luminosity – may appear equally bright!

  12. On the other hand . . . two stars that differ in brightness need not differ in luminosity.

  13. Brighter Dimmer How much dimmer? How much brighter?

  14. d L Sphere, radius = d Flux (F) amt. of light energy flowing per second through 1 m2 1 m2

  15. = All of star’s light must pass through sphere . . . So the energy is spread over the sphere’s surface. Amt. of energy per sec through 1 m2 Total energy per second flowing Total number of sq meters Inverse-square law of light!

  16. d d (ly) F (watt/m2) For a given star (i.e., specified luminosity): 1 2 5 10 100 25 4 1

  17. Flux & distance  Luminosity  Sun’s flux at Earth: F = 1370 W/m2 d = 1 AU = 1.5 x 1011 m L = 4(1.5 x 1011)2 x 1370 = 3.9 x 1026 Watt (!)

More Related