For a galaxy 200 Mpc away, a useful standard candle would be the ...

[kshipps]

For a galaxy 200 Mpc away, a useful standard candle would be the ________.
 
  Fill in the blank(s) with correct word

Question 2

Describe how Eratosthenes first measured the size of Earth over 2000 years ago.
 
  What will be an ideal response?

[cclemon1]

Answer to Question 1

Type I supernova

Answer to Question 2

Eratosthenes used measurements of the angle of the Sun in the sky at noon on the summer solstice in two places in Egypt. It was directly overhead in Syene and cast no shadows. In Alexandria, however, there was a slight shadow, indicating that the Sun was 7 degrees away from overhead. Eratosthenes concluded that Alexandria lies at a latitude 7 degrees north of Syene. The circumference of Earth is then the distance between Syene and Alexandria divided by the fraction of the circle (7/

[kshipps]

Thanks for the timely response, appreciate it

[marict]

Excellent