The answers to the questions for the students posed in the instructions for
the activity are below. Keep in mind that for some of the questions there
isn't a right answer. The question is merely intended to stimulate a
discussion.
- Part 1
- What if there is a lot of stuff out there which is not shining? How
can we learn about it?
- This question is meant to get the students
thinking about how matter which can't be seen directly--known
scientifically as dark matter--might be detected. The answer is through
its gravitational effect. Even matter which cannot be seen can be
detected through the gravitational pull it exerts on nearby objects.
The planets Neptune and Pluto were discovered when astronomers were
unable to completely account for the motion of known planets, and
deduced that there must have been additional planets pulling
gravitationally on the known planets.
- How close did you get to the inverse square law?
- The answer to this question will, of course, depend on what data the
students take. Many students find that brightness does not fall off as
quickly as the inverse square law would predict.
- If your points are different from this curve [the inverse square law]
what do you think might have caused the difference?
- This would be a very difficult question to answer precisely.
However, there are a number of reasons why brightness might not fall off
as quickly as the inverse square law would predict:
- There will
be more than one desktop star in the room, and unwanted light may be
entering the detector.
- The inverse square law really only
applies to a point source of light, and in a light bulb the light comes
from a filament approzimately a centimeter long.
- Some of the light from
the desktop star will reflect off of the box in which it is enclosed and off of the
table on which the apparatus is resting. This "extra" light may also enter the
detector.
This is a good question to get the students thinking about: why
don't experiments always go as expected? This brings home the
fundamental difficulty
of experimental work.
- Part 2
- Part 3
- How old is the universe?
- The universe is believed to be approximately 12 billion years old,
though testimates range from 10 billion to 20 billion years.