Easy Questions?

[Swatopluk]

You probably know that situation. You take something for granted and then somenody (often a child) ask you "Why.....?" and you run into trouble explaining (even if it is not the traditional origin of holes in cheeeeeese question).

I propose this thread for the discussion of everyday things like that.
This could be run as a competition/game with some readers trying to explain the current question while others try to poke holes into it.

For starters:

What is farther from the Earth? Sun or Moon or does it change?
How can you prove it with simple methods that a child (or pre-radar person) could understand? How could you estimate the relative distance of Sun and Moon to Earth and their actual relative sizes?

medium:
How can you show that the Earth is roughly spherical?
How can you calculate the size?
How can you show that the Earth is slightly flattened? (Pole to Pole shorter then from one point on the equator to the opposite point)

For experts:
Why is it dark at night?





Edited: to clean up title. Mero.

[goat starer]

I thought about these questions for a while and then realised I am too stupid to answer them and gave up. I did work out that the moon must be further away as it is less bright and everybody knows that the further away a light is the less it illuminates.

Can we have some biological / nature easy questions please?

[Griffin NoName]

Easy questions indeed. My elder son asked me these very questions aged three. He started with the final question and my answer led him to asking the first two (try reconstructing my answer from that!!). We also had a discussion about the sun going round the v. the earth going round the sun. He grew up to be a physcist. I was a little relieved when my second son arrived and did not make such enquiries. Indeed when playing Trivial Pursuit, the question being what is 93 million miles away from the earth, his answer was Manchester (for those of you who do not realise the relationship between the North of England and London this may seem a strange answer but actually it showed a fine appreciation of British society for a four year old). He grew up to be a civil servant!!!

Paaaaaarr!!!  I'm not even going to try to answer these questions. I'm still exhausted from answering them all those years ago

[Sibling Kephra (Tansy)]

You know what's funny?  I can only take a stab at the last one.  lol
I homeschooled my kids for two years and had to show about day/night, the moon's orbit, etc...

I got out a globe, a small ball, and a flashlight.  Turned off the lights and turned on the flashlight.  Shone it on the ball with the ball being in between the light and the globe.  Then moved the light around.  My kids could clearly see the 'phases' of the 'moon' as I did this.

Actually come to think of it this would be a way to prove to a child that the sun is farther away than the moon as well.  It proves that the moon is closer, because it goes 'dark' to 'light' due if being in betwen the sun and the earth.

[Swatopluk]

the main problem for thew sun/moon question would be that it is difficult to prove that their distance from us is constant. How do we know that the moon is not sometimes behind the sun. They seem to be or roughly equal size with small variations over time (difficult to see with the sun without going blind of course).

The easiest way to show that the sun is much farther away I came up with is the solar eclipse. It is only visible as a total in a rather narrow strip bordered by strips of partail eclipse. the breadth of this strip is connected to the relative distances. If the sun were directly behind the moon (i.e. (earth -> sun)-(earth -> moon) = very small) the strip would be very wide and the farther the sun is behind the moon the narrower it would be.

All of this would of course need the assumption that distance and appartent size are inversely proportional and that celestial bodies do not change their size on a regular base.

The darkness at night is actually a very difficult question that requires a lot of cosmological models to solve (Olbers paradoxon)

I'll address the Earth size in a later post.

[Bob in a quantum-state-of-faith]

For experts:
Why is it dark at night?

Don't you know? So that one can fly up and study the Sun, and not get all sun-burny.  Silly.


______________________

Seriously, the spherical-earth can be demonstrated by ships at sea. 

First, it should be demonstrated that water, if no other forces are acting on it, will seek a level surface - that is, it will always assume a flat surface.

Therefore, the sea's surface can safely be assumed to be flat in relation to the Earth's surface.

If the Earth were a flat plane, then a ship sailing directly away from an observer, would appear to become smaller and smaller, until it became a tiny dot. 

THIS phenomena can be demonstrated by birds in flight.  Especially, if you observe birds taking off from a landed position, and they begin flying higher and higher and farther away.  This keeps them in visual range longer, before they go below the horizon.  But, their apparent size diminishes over distance.

Back to the ships.  What is actually observed, is not that the ships appear to grow smaller, but that the ships seem to sink into the sea.  They do get smaller, but long before they disappear as a dot, they "sink" below the wave-tops.

The first time this was observed, the observer may have concluded that the ship did indeed sink.  However, when the same ship made a return journey, the reverse happened:  the ship appeared to rise out of the sea as it's apparent size increased.

Upon questioning the sailors, the observer would have to discard the idea that the ship sank, as the experience of the sailors was that the ocean always appeared flat, and it was the LAND that "sank" into the sea. Or at least appeared to.

There are two obvious explanations for this observed situation.  The sea has "dips" in it near to land masses, and the ships sailed into these dips.  However close inspection of smaller bodies of water, such as lakes or ponds, no dips are ever observed.  Moreover, these dips cannot be recreated by manipulating the bottom of the container, either.   

That leaves the other obvious explanation:  the actual Earth itself is curved, and the water clings to it's surface by the same forces that hold other objects down, such as people, rocks and, indeed, ships.  A curved surface would neatly account for what is observed by both the land-based observer, and the sailor on the ship.

A diagram, with visual sight-lines can demonstrate how this works better than words.

[goat starer]

that shows that the world is curved but not that it is spherical

[Bob in a quantum-state-of-faith]

that shows that the world is curved but not that it is spherical

True.  But a sphere is much more logical than an upside-down dish, is it not?

[Griffin NoName]

I like topic drift. I am now considering whether spheres and/or upside-down dishes can be logical - in the sense of thinking in a logical way. My initial gut feeling is yes. Although I think it's easier to prove for an upside-down dish than a sphere. I've a feeling this proof would need to rely on some of Aggie's Hyper theories and probably needs a separate thread.

[Swatopluk]

The classical proof/calculation of earth shape/size is the measurement of the angle of the sun over the horizon at noon in different places with known distances and relative positions. For a strict proof it would have to be at least 3 positions not located on a single straight line and not symmetrical to the path of the sun. That's the only simple idea I came up with to show that the curvature is different in east-west from north-south (slightly flattened sphere).

The "sinking ship" method has one disadvantage. It could be that the light has a tendency to either follow the surface or be drawn away from it, i.e. the rays of light could be curved slightly instead of being straight lines. Of course it is possible to disprove it but some effort would be needed.

Btw, all methods imply that it is possible to determine the exact direction to the center (if the earth's core would be asymmetrically positioned that could be tricky because the lead on the line would point into the wrong direction).

You see into what trouble one can run with "easy questions"

[goat starer]

If you knew we would have trouble why did you ask them. I will be sending you the bill for my councilling and psychiatry. 

[Swatopluk]

I expected to be paid the same way (despite us not being a flagellating order). My solutions to the problems probably leave a lot to desire anyway. I thought of this thread more as a discussion catalyst than a sadistic riddle game. There were e.g. a few interesting aspects in Bob's post I had not thought about and there should be an easier way to determine the curvature of the Earth than differential solar bearing.
I hope it did not look like a vanity exposition to show my superior knowledge/intellect. The "how to explain 'easy' things to children" problem is quite a real one.

[Griffin NoName]

OK, time to reveal the answer that will not satisfy a 3 year old - why does it get dark at night - because the sun disappears over the horizon..... (I thought that was about as much as a 3 year old would comprehend).... well he knew what a horizon was, he wasn't bothered by that bit, just wanted to know why does that happen... that's when the trouble started

Yes it is extremely hard to explain such easy questions.

In fact there may well be a need for a handy pocket book for distressed parents.

[Swatopluk]

In fact there may well be a need for a handy pocket book for distressed parents.

Probably lots of them on the market but those little brats come up with new questions faster than the printing press will satisfy the demand.

Another classic (in German) is the question about the Anglo Saxons.
The German term Angelsachsen is confusing because there are already two Saxonias in Germany (Sachsen and Niedersachsen) and angeln means fishing with a rod.

[beagle]

Here's one I've never understood. Why is it that when you leave biscuits and cake out of an airtight box the cake goes like biscuit, and the biscuit goes like cake?