1. What is parallax?
- Parallax is the apparent displacement / change of an observed object due to the changed position of the viewer, that provides a new line of sight.
2. What is luminosity?
- Luminosity is the relative quantity of radiation emitted by a celestial source. (as a star)
3. How do we measure stellar luminosities?
- We measure stellar luminosities by measuring a star's apparent brightness and distance, we can compute its luminosity with the inverse square law of light. Parallax tells us distances to the nearest stars.
4. How do we measure stellar temperatures?
- We measure stellar temperatures by a star's color and spectral type; both reflect its temperature.
5. What is a Hertzsprung-Russell diagram?
- A Hertzsprung - Russell Diagram (H-R Diagram or HRD) is a scatter graph of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures. Hertzsprung–Russell diagrams are not pictures or maps of the locations of the stars. Rather, they plot each star on a graph measuring the star's absolute magnitude or brightness against its temperature and color.
6. What is the significance of the main sequence?
- The significance of the main sequence is when normal stars that fuse H or He in their cores fall on the main sequence of an H-R Diagram. A star's mass determines its position along the main sequence. (high mass: luminous and blue; low mass: faint and red)
7. Who was Ejnar Hertzsprung?
- Ejnar Hertzsprung was a Danish chemist and astronomer who classified types of stars by relating their color to their absolute brightness—an accomplishment of fundamental importance to modern astronomy. The Hertzsprung-Russell diagram of stellar types was named (in part) for him. In 1913 he established the luminosity scale of Cepheid variable stars, a tool for measurement of intergalactic distances.
8. Who was Henry Norris Russell?
- Henry Norris Russel was was an American astronomer one of the most influential during the first half of the 20th century—who played a major role in the establishment of modern theoretical astrophysics by making physics the core of astrophysical practice. Who, along with Ejnar Hertzsprung, developed the Hertzsprung–Russell diagram in 1910. This is a graph that demonstrates the relationship between a star’s intrinsic brightness and its spectral type and that represents Russell’s theory of the way stars evolve. In 1923, working with Frederick Saunders, he developed Russell–Saunders coupling which is also known as LS coupling.
9. What is the mass of Betelgeuse?
- The mass of Betelgeuse is 7.7–20[7] M☉. Betelgeuse is about 18 or 19 times the mass of our sun.
10. What is the parallax of Sirius?
- The parallax of Sirius is 379.21 ± 1.58[2][5] mas. This can also be translated to 0.377 (0.38) arc seconds.
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