Class 3, ICA #2, August 28.

We did Prather et al. pages 131 and 132,
and had 7 clicker questions,


Clicker Question #1:  This was the first question of the reading check.

A scale model of the whole Solar System that has the Sun as a 
grapefruit would

B. stretch across campus.



Clicker Question #2:  This was the second question of the reading check.

Our Milky Way Galaxy

D. has not been seen from the outside by us.





Clicker Question #3:  

(Twin question on slide 7.)

B. 11 years old.

Why: Today you get the announcement that B is 13 years old.
How old is she really? 16. How old is A really? Also 16 --
they're twins after all. But A is 5 ly away, so if she
is really 16 right now, and it takes 5 years for a message
from her to get to you, how old must she be now? 




Clicker Question #4:

(Prather et al. #6 on page 131.)

D. Crystal sent first. 




Clicker Question #5:

(Prather et al. #8b on page 132.)

D. 40 million years from now.



Clicker Question #6:

(Prather et al. #8c on page 132.)

D. 60 million years ago.



Clicker Question #7:

(Related to Prather et al. #9 on page 132).

A. X is older.

Why: Suppose they both appear to be 5 years old.
Say Y is 3 ly away, and X is 5 ly away. How
old are X and Y really?


All answers to Prather et al. 131-132:

#1: Light-year is a unit of distance, the distance
light travels in one year.

#2: Sydney lives 4.3 ly from the Sun.

#3: 11.4 years -- Crystal's picture takes that long.

#5: Yes, the farther away the child lives, the older he/she
is when you actually receive his/her message.

#6: Crystal sent her picture first and Sydney sent her picture last.

#7: As it wasy 2.5 million years in the past. Light takes
that long to travel the distance between Andromeda Galaxy and here.

#8: 10 million years, 40 million years, 60 million years ago.

#9: a and e