Making “skyentific” observations with a
cell phone
Observation
It’s quite possible to make scientific
observations of different natural
phenomena in everyday life: all you need
for it is to document the observation and
make certain measurements. Here we
will focus on making observations with a
device that most pupils carry around with
them: a cell phone. One example of a
natural “skyentific” phenomenon that
can be documented with a cell phone is
the rainbow.
In an ancient Greek the universe was
divided into two regions:
* A spherical Earth, central and
motionless (the sublunary sphere).
* A spherical heavenly realm centered
on the Earth, which may contain multiple
rotating spheres made of aether
All sky phenomena belonged to the
astronomy. So rainbow is a sublunary
astronomical phenomenon.
Exploration
Impressive photos of a rainbow can be made even on a cell phone camera. It’s advisable to
encourage pupils to take photos of rainbows during the summer holidays. In the Fall, while teaching
optics on physics lessons, one could even hold a photography contest. This is the situation especially
in the northern countries like Finland. It is also in many cases easier to study optical phenomena
from a good photo than in a nature. And as it was said, especially then, when the phenomenon is
rarely seen.
So here the photos and videos of a rainbow a the starting point of study. You can not solve the
nature of rainbow jus watching photos, but you can make good observations, which can lead to the
good questions. The answers are in experiments, that you can make or you can read what other
scientists have done earlier. That is how science goes.
The rainbow is a light phenomenon that covers practically the entire field of optics from colours to
interference. It provides innumerable questions and topics for research on lessons of physics, history
and even religion.
Here are some questions that photos of rainbows might evoke:
1. What part does the rainbow play in the Bible?
2. How do the appearances of the rainbow in
the Bible relate to physics?
3. In what angle is the first rainbow visible and
why is this? In what angle is the second rainbow
visible?
4. Why couldn’t a pot of gold be found at the
end of the rainbow?
5. What is the darker area between the first and
second rainbows called and what is the reason
for it?
6. One can see colourful thin bows below the
rainbow. What are they and how do they come about?
7. Is the mirror image of the rainbow in the water reflected from the same raindrops as the real
rainbow?
8. Why can’t a rainbow be the result of a total internal reflection (as erroneously stated even in
many textbooks)?
Concept introduction
The rainbow is a complex natural phenomenon,
and it took well over two thousand years for
scientists to solve its mysteries. The first
explanations of any scientific value were made by
Greek philosophers about 2500 years ago. And the
last word on the matter has not been said yet, as
there are still many unexplained questions about
the rainbow.
Here, however, are answers to at least some of
the questions, as well as references to sources of
knowledge. Some of the questions can be quite
demanding even for high school students, while
others are suitable for pupils of elementary school.
1. According to the Old Testament, the rainbow is
a sign of the covenant: God produced the rainbow
on the sky after the deluge as a promise that it
wouldn’t happen again.
2. In order for the rainbow to appear on the sky
after the deluge, God would have had to change
the optic qualities of water from what they were
during it – in other words, reading the Bible as a
textbook of natural sciences leads to rather absurd
explanations. This might be a good moment to explain to pupils that science and religion deal with
two different aspects of human life and their premises are fundamentally different from each other.
3. The appearance of a rainbow is a complex optic phenomenon. It was first solved in a somewhat
sensible way by the famous 17th century French scientist and philosopher René Descartes. There is a
lot of material to be found about the rainbow in both books and on the Internet. Here’s one link to
start out with:
http://en.wikipedia.org/wiki/Rainbow
There is at least one book in Finnish about the rainbow that is intended for the general public. The
book has been sold out ages ago, but it’s worth keeping an eye on in second-hand bookshops:
4. Rainbow is not an immutable object, but a series of reflections of waterdrops seen from a certain
angle. As the viewer moves, the rainbow moves as well, which makes it impossible to find ”the end
of the rainbow”.
5. The dark area between two rainbows is called Alexander’s dark band. It is in the direction where
light beams are not reflected from raindrops. A good explanation about the matter can be found
also here
http://en.wikipedia.org/wiki/Rainbow.
6. The thin bows are caused by interference. Their
origin was discovered by scientist only in the 20th
century. More on this phenomenon can be found
here.
http://en.wikipedia.org/wiki/Alexander's_band
7. The rainbow reflected in the water is a reflection
from different raindrops and is thus a ”different
rainbow”. A good explanation about this and many
other phenomena can be found in M. G. J. Minnaert’s
classical work Light and Color in the Outdoors:
8. The reasons for this being so are numerous.
a) Light is always reflected in the same angle inside a
raindrop. If it’s reflected once by total internal
reflection this recurs always in the same way and the
light is ”captured” in the raindrop.
b) The rainbow would be much brighter if the light
would be fully reflected in the raindrops.
c) The rainbow would be seen at a different angle if
the light would be fully reflected in the raindrops.
Generalization of the concept
It’s usually impossible to capture an entire rainbow on a cell phone camera. For doing that, the video
camera on a cell phone may come in handy.
Rainbow video