Question

1. What is your interpretation of "looking at distant objects only strictly tells us about their past, not the present" ?

2. Name and describe, in very simple terms, the three main methods we use to find/discover distant planets.

3. It is mentioned that if Sirius (the brightest of stars for us) indeed has the same intrinsic brightness of the Sun (as postulated by Huygens), but is observed by us as 600 million times fainter, it's distance should be about 25,000 times further than the Sun. That's from the law that says that light gets dimmer as the distance squared. 25,000 time more distant than the Sun is a distance of about 0.4 light-years (please recall that the Sun is about 8 light-minutes away. How far is Sirius from us? Based on its true distance, what must this therefore really mean for Sirius's intrinsic brightness?

Answer 1

A) Stars are so far from us that it takes year to light reach to us. So what we observe in stars are event that happened years earlier. So we only see their past, not present.

B) Three method to discover distant planet are

1. Radial velocity method

2. Transit photometry

3. Direct imaging.

C)