"Seeing" the Earth, Moon, and Sun to Scale
The
moon is about 1.3 light-seconds away (240,000 miles). Here is a scale
picture of the Earth-moon system, with the earth (actual diameter: 8,000
miles) represented by a circle just a little bigger than 1/8 inch:
(Remember
this picture the next time you watch the movie Apollo 13!)
The
sun is 8.3 light-minutes away (93,000,000 miles). A scale drawing
is not as easily made here as it was for the Earth and moon above. If
we chose the same 1/8 inch diameter circle to represent the earth, then
we would require a circle bigger than one foot in diameter to represent
the sun (actual diameter: 864,000 miles). The center of the sun circle
would have to be placed about 121 feet from the center of the earth
circle! You can begin to be impressed by the different sizes and separations
that we encounter in space.
The
terms light-seconds and light-minutes are used as units
of distance along with light-years. These units may be understood
as distances, or in another way. When we look up, we see the moon and
sun, not as they are now, but as they were 1.3 seconds
and 8.3 minutes ago, respectively. Hence, the concept of the space-time
continuum: the further out we look into space, the farther back we
see into time.