If you can, please keep any explanations simple (if possible) so I can understan

Question

If you can, please keep any explanations simple (if possible) so I can understand them. I'm a bit of a beginner in studying this stuff.

1- Explain why would a star would appear to move among the distant stars as earth orbits the sun counterclockwise from January of one year, through July, to January of the following year.

2- Consider two stars (C and D) that both exhibit parallax. If star C appears to move back and forth by a greater amount than star D, which star do you think is actually closer to you?

3- Who is correct? Student 1 thinks a star with an apparent magnitude number of -2.0 would look brighter than a star with an apparent magnitude number of +1.0. Student 2 disagrees, saying the bigger the number the brighter the star and that the +1.0 star would look brighter than the -2.0 star.

4- If a star has an apparent magnitude of -26.7 and an absolute magnitude of 4.8, where might this star be located and what is the name of this star? Explain your reasoning.

5- Stars A and B have the same surface temperature. Given that star A is actually much more luminous than star B, what can you conclude about the size of star A compared to star B?

6- Star A has a greater surface temperature than Star B. Given that Star A is actually just as luminous as Star B, what can you conclude about the size of Star A compared to star B?

7- If you were given a star’s absorption line spectrum and its corresponding spectral curve shown on an energy output per second verses wavelength graph, how could you approximate the temperature of the star?

Explanation / Answer

1. while the earth moves from January of one year to july of the same year around sun, it moves about half the distance of its orbit and hence these two positions would be two extreme ends of its orbit around sun. In this time any star would appear to move by some degrees relative to the background as the line joining the observer from earth, the star and any point on the background would rotate by a few degrees due to motion of the planet earth. so, if we consider the star appears to have moved by some degrees to the right in this duration, then the star would again start to move towards left from july to january and come to the swame initial position in january next year

2. for parallax, greater the distance from the planet, lower is the parallax angle ( back and forth) moved when the earth completes one full year's orbit around the sun. Hence as C appears to move more back and forth relative to D, C is closer to earth than D

3. the apparent magnitude of a star follows an inverse relation with the brightness, so lower the apparent magnitude of the star, brighter it is

henceStudent 1, who thinks a star with apparent magnitude of -2 will be brighter than the star with apparent magnitude +1 is correct

4. given apparent magnitude = m = -26.7

Absolute magnitude, M = 4.8

now, from the relastion between apparent and absolute magnitudes

M = m - 5(logd - 1)

where d is distance in parsecs from the star

so,

4.8 = -26.7 - 5(log(d) - 1)

d = 5.01187*10^-6 parsec

now 1 parsec = 3.26156 light years

so d = 1.63465*10^-5 light years = 8.5917 light minutes

so light takes about 8 minutes to reach from this star to earth

hence this star is the SUN

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