1. Explain the difference between Optical Double stars and True Binary Stars.
show answer
- True Binary stars are linked together Gravitationally and orbit a common centre of mass.
- e.g. Castor in Gemini.
- e.g. Algol in Perseus.
- Optical Double stars merely appear nearby but may be light years apart.
2. How many times brighter is a star with a magnitude of 5 compared with a star with a magnitude of 1?
3. What is Pogson’s ratio?
show answer
- The difference in magnitudes is the 5th route of 100 which equals 2.51
4. Give 4 factors that affect the apparent magnitude of a star.
show answer
- Energy radiated by star
- Interstellar gas and dust.
- Amount of light absorbed by Earth’s atmosphere.
- Distance from Earth
5. What is the magnitude of the brightest star in the sky?
6. What is the Absolute Magnitude?
show answer
- A measure of Apparent magnitude if observed from a distance of 10pc
7. Name two types of variable star.
18. What is a True Binary?
show answer
- Two Stars orbiting around their common centre of mass.
19. What is a Cepheid Variable?
show answer
- A giant yellow star that regularly expands and contracts in size.
20. What is an eclipsing binary?
show answer
- If two binary stars orbit each other in a plane along our line of sight, two stars will eclipse each other.
21. What is the Primary Star?
22. In what way is the variability of light intensity of Cepheid Variables different to that of eclipsing binaries?
show answer
- One is due to the star pulsating (Cepheid)
- The other is due to stars eclipsing each other (eclipsing binaries)
23. Draw the light curve of a Cepheid Variable.
24. Draw the light curve of a Eclipsing Binary.
25. What is Parallax?
show answer
- The apparent motion of near and more distant objects in respect to each other, caused by the motion of an observer.
26. Describe the method of heliocentric parallax to determine the distance to nearby stars.
show answer
- We measure the angular shift in position of a star from E1 to E2
- Half of the angular shift is called the parallax angle (p)
- Then we use the formula d=1/p
- Distance (in parsecs) = 1/ Parallax angle
27. What is the definition of a parsec?
show answer
- The distance at which a star would have a parallax angle of one arc-second.
28. Describe how Cepheid Variables can be used to determine stellar distances.
show answer
- Using the period – luminosity law we can work out the absolute magnitude of the star
- Use the distance modulus formula to calculate distance.
