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WNCC in
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You can do these activities at home with household items. It's
fun too when you have young children in the house. Just make sure
to explain concepts correctly to them. If you are not sure yourself
(after all, you're the learner in this class), do not make up anything
but rather say "I don't know myself, but I'll ask the instructor".
Notice that I substitute astronomical names for household items on
and off. I do that so that while you play with apple and grape you
still remember that this is about Earth and Moon.
M0 Gravitation
you need: a non-breakable object ;
Also, if you have: globe and two small toy figures to temporarily attach to the globe (one on the Northern, the other on the Southern hemisphere; check the photo in my lecture on gravitation) - as a reminder that Earth's gravity attracts both and how it would look like from space.[You don’t drop the globe, you just use it as something to look at while you do the experiments.]
This experiment may seem kind of infantile to you. However, I know from experience that most people have not understood gravitation completely.* So be as diligent as you can. (All footnote questions are answered with yes.)
Check my lecture on gravitation.
A non-breakable object is dropped from a height of 5 to 6 feet.
Describe the object's motion as accurately as you can ...
Why does it fall?
Why is it accelerated?
Does it fall downward? Why is this a strange description?
Or does it fall towards Earth? Why is this description more precise?
Why towards Earth? Is there anything special about Earth?
* E.g. is there gravity on our Moon?
Does our Moon attract Earth? Does our Moon "fall" towards Earth?
Are astronauts in the Space Shuttle attracted to Earth? Do continents
on Earth experience a tidal force as well? Does each object with
mass exert a gravitational force? Examine the lower
right panel of these stamps: what's wrong about the title "Escaping
the Gravity of Earth" in conjunction with the picture shown?
M1 Seasons:
you need: Earth globe, bright lamp, 3 to 5 feet long string
Shine a light (lamp without the
cover, our Sun) onto the globe. Turn off all other lights.
As you turn the globe, you notice day and night.
As you move the globe around our Sun, make sure that the distance stays the same (that's what the string is for) and that the globe's axis points to the same spot in the room at all times (very important!; e.g. a corner between walls and ceiling - that would be the place of the North Star, Polaris, in the Little Dipper).
Start at the position where the axis is pointed at the corner and is
also
tilted away from our Sun. Notice that the lamp shines
directly onto the Southern hemisphere (heating
it up), but makes a rather shallow angle on the Northern (keeping
it colder). Put your finger onto your home town and rotate
the globe so that our Sun rises and sets. Notice that the day is
rather short. Put your finger on
Orbit the Earth around our Sun to the opposite side. Make sure that you keep the distance constant and that the axis points towards Polaris. Also, rotate the Earth 182 or 183 times as it makes this half orbit (hey, just kidding; but it would be proper).
Now notice that the axis is pointing still at Polaris but relative to our Sun, it's tilted towards that as well. Repeat the same as described in the second paragraph: you'll notice you have summer in the Northern and winter in the Southern hemisphere (where they have mild winters because all land masses are rather close to the equator).
PS With the string you will be able to describe a circle around
our Sun. Now you've read that Earth's orbit is elliptical.
But only very slightly. If your string is 30 inches long, it is shortened
by only one inch during January (getting Earth a little closer).
M2 Eclipses:
you need: light bulb (take off lamp shield) - apple - grape
Turn off all lights at night except that one light bulb. Then have the grape eclipse the apple in such a way that a path is drawn across the Earth by the orbiting Moon, thus only certain regions on Earth see the eclipse. Keep the grape orbiting the Earth at the same distance, but not horizontal, instead slightly tilted. It must then align again on the other side (since the orbit is closed). Notice that this lunar eclipse, two weeks later, can be seen from the entire apple's night side.
Furthermore (this may be hard to
do, perhaps exaggerate it a little; check the six animations in my lecture
script VIT eclipses): as the grape still follows a tilted orbit,
Earth orbits the light bulb Sun as well (about
30 degrees to the next new Moon, grape between apple and light bulb
again), so that our Moon is now too high or too low for an
eclipse when it gets between the apple and our Sun.
M3 Moon's phases:
Instead of the grape use a round object that has a lighter color so
that it reflects better. Again, just one light bulb. Notice
that wherever you hold the object, half of it is lit up (make
sure that nothing obstructs its view from the Sun). Use your
own head as the Earth. As the object is orbiting your head at arm's
length (to avoid too many eclipses),
turn your head with it. Notice how the phases develop as the Moon
changes its position relative to Light bulb and egghead (sorry,
but when I use the spell check it always inserts "egg").
Thanks to Brian Brink for his suggestion.
M4 Model of solar system:
see my Very Important Topics.
M5 Lenses and Mirrors:
eye glasses - reading glasses or bifocals – magnifying glass - small
glass filled with water and very little powdered milk - make-up mirror
– car’s side view and rear view mirrors
This is just an incomplete optics lesson as you can only do limited exercises with these household items (no need to dismantle your car’s mirrors).
Use normal eyeglasses (“normal” ones are for shortsighted people as most of us are; they are concave), hold them above some printed text.Describe the size of the print.
Use the inner part of bifocals, the reading glasses (used by farsighted people and by people who cannot focus on near or far objects; they are convex), or the magnifying glass.Hold them above some printed text.Describe the size.Interestingly, if your eye is far enough away and you move the glass further away from the text, it will eventually become blurry, then reverse.
Refractors use convex lenses, not because they magnify (which is nice too, though), but because they converge the light.
Use the make-up mirror (it’s a concave).Get near, then move your face slowly away.Compare your observations with the lenses above.Of which lens is this reminiscent?
Use the side-view mirror or the “surveillance” mirror in a store.What do they show?
Which of these kinds of mirrors would you use for a reflector?
Use the small glass filled with water and very little powdered milk or strong eyeglasses.Look at a light-bulb through the hazy milk-water: it appears reddish (for the same reason, a sunset is red).Look through the milk-water from the side: it appears bluish (for the same reason, the sky looks blue).Look through the eyeglasses from a large angle: you see all colors.All these effects are produced because lenses are dispersing light (fanning it out into its colors).Which telescope, refractor or reflector, could thus be described as slightly inferior?
This doesn’t have to do with astronomy but it’s kind of interesting: you know that when you flip the rear-view mirror, the brights of the car behind you are dimmed.See http://newton.dep.anl.gov/askasci/eng99/eng99059.htm .
A former student told me that a teacher
in
M6 Satellites
Try NASA's satellite tracking applet: http://liftoff.msfc.nasa.gov/RealTime/JTrack/Spacecraft.html
Warning: download times can be
very long and it doesn't work if your browser is too old or your computer's
RAM is too small! But you'll love it once it's running.
Geostationary
satellite to broadcast the Olympic Games from
M7 Solar
Spectrum (online):
see Lab F6.
M8 Binary Stars (online):
Enter the following parameters for the "Eclipsing binary stars" animation for:
Sheliak (bLyrae)
Get spectral types from SEDS
in Arizona.
Inclination is 10 degrees, Separation is 22 million
miles (50 solar radii).
Move the screen down, so that the animation is OFF
screen and you see only the "light curve".
Observe what happens to the brightness as they eclipse
each other.
Change the inclination to 0 degrees: what is it
about the eclipses (in the lightcurve) that
gives away the radius?
Which data would give us the mass of these stars?
Which law do we have to use?
See also my lab A4 and my script Measuring Stars, both about Algol (bPersei).
A chart for Sheliak and Lyra is at GOI's ASTRONOMIE-SEITEN (in German), a beautiful photo is at Catalunya (in Spanish; it's a quiz).
PS Do you know the "Sheliak"?
It's Arabic for "Tortoise". And the writers for Star Trek: The
Next Generation used it for some intelligent life form; it's all over
the internet.
M9 Birth of Stars:
bicycle pump - bicycle tire
Objective: As an interstellar cloud (and eventually the protostar that forms from the ISM) contracts, temperature increases because not all the heat produced from the gravitational energy is radiated. Besides the increase in temperature, pressure rises too. This pressure will eventually balance gravity, which then makes for a stable star. And finally, temperature will reach the necessary 10 million Kelvin for Hydrogen to ignite.
Procedure: Let out some air from a bicycle tire. With a bicycle pump inflate this tire until you're exhausted. Give 20 strokes - you shouldn't overwork yourself. Note that as you compress the air, the tire pressure increases (of course it does - that's why you do it). When done, feel the nozzle of the pump: it will be quite warm, indicating that temperature rose as you compressed the air.
Now, what does this have to do with stellar formation?
Telescope Powers
Discuss why magnification is not that important as one may think.
Telescopes sold at department stores are advertised falsely as 525x magnification. They have an aperture of 60 mm (2.4 inches) which gives a maximum possible magnification of 120x. Discuss how the advertised wrong magnification conflicts with the resolving power of the telescope.
Seasons
Compare our Sun's arc through the sky during summer with that during winter. How can this be explained by the tilt of the Earth's axis?
It is hard to convince people that the Earth's distance to our Sun is approximately the same throughout the year.* You don't have the means to really measure the distance (unless you own powerful radar equipment, or are able to measure our Sun's parallax from two locations on Earth). But you can measure how big our Sun appears in the sky. How? And why is that a measurement of the distance as well?
Why do we not associate snow with "Down Under"?
* After all, the closer you're to a camp fire, the warmer you get. However, we're not getting any closer to our Sun during summer (in fact, we're farthest away in early July).