Distances to Stars Parsecs and Light Years The
- Slides: 15
Distances to Stars: Parsecs and Light Years
The Stars are other Suns “L’amor che move il Sole E le altre stelle”… Dante, end Of Paradiso Or…the Sun is the closest star Think about them: Demo of “Starry Night”
Basic Questions about Stars • • • How far away are they? How hot are they? How massive are they What are they made of? Do they have planets too? How do they change with time (stellar evolution) 16 Cygni
Most Basic Method of Stellar Distance Determination Trigonometric parallax: an ordinary surveying technique Figure 16. 1 of textbook, and Section 16. 2 DEMO
The concept of parallax and distance measurement
How big is the angular shift? s Th r If Th << 45 degrees, Th (in radians) = s/r 90 degrees make a right angle 60 arcminutes made one degree 60 arcseconds make one arcminute
The values of stellar parallax Smaller parallax > greater distance Largest parallax = 0. 75 arcseconds 1 arcsecond = dime at 1. 3 miles
Alpha Centauri, the closest star
How close/far is Alpha Centauri, and what units do we use to describe its distance? • 1 parallax-second = 1 parsec = 3. 08 E+16 m =206, 265 au. Alpha Centauri is 1. 33 parsecs • If 1 au were 1 cm, Alpha Centauri at a distance of 1. 5 miles • The Light Year = (2. 9979 E+08 m/sec)*(3. 156 E+07 sec) = 9. 461 E+15 m. Alpha Centauri is 4. 3 light years away • 1 parsec = 3. 26 ly
Think back to descriptions of solar system distances (light minutes to light days) and compare the situation for nearby stars to get an idea of the immensity of interstellar space
Sources of Parallax Measurements • Pre-1990: groundbased telescopes, ~ 1000 stars measured • Hipparchus: 118, 000 stars measured • See book for breakdown on precision (section 16. 2 of book)
What distances do we have for the nearest stars? • • Appendix 11 of book Abbreviated Version Star Alpha Cent. Sirius Altair Vega Arcturus Dist. (ly) 4. 3 8. 8 16. 6 26 36 Dist. (pc) 1. 3 2. 7 5. 1 8 11
Look at Appendix 12 (distances to brightest stars) and think about the significance of those data
What are the distances to the stars in Cygnus?
Distances to the Stars of Cygnus 990 pc 3. 5 pc 22 parsecs 17 pc 125 pc 467 pc 52 pc
- Apparent magnitude equation
- Astronomers measure large distances
- There are millions of stars in
- Light light light chapter 23
- Light light light chapter 22
- Light light light chapter 22
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- Sheep years to human years
- 300 solar years to lunar years
- Two towers face each other separated by a distance d=20
- It measure the vertical distance
- Equal distances covered per unit time
- Iso 11620
- Easterlies
- Counterclockwise hexagon agility test
- Nfpa separation distances