ingridscience

Tell students that as a crystal grows, the atoms add on in a regular way. Depending on the pattern that the organize in, different shaped crystals are made.
This activity uses building toys to show how a regular arrangement of smaller units can make some common crystal shapes.
When you build, make sure that you add the units in the same repeating pattern (show example).
See which crystal shapes you come up with.

Students model two masses orbiting together. They represent the coupled orbits of two stars (a "binary star system"), or a star orbiting a black hole, or a planet orbiting a star. The movement - the orbit path and speed - of each mass depends on the relative sizes of each object.

Tell students that they will investigate coupled orbits, to discover how orbits and speeds vary with the masses, and then find out how astronomers study couple orbits to discover objects in the universe.

Give students the equipment, ask them to add masses to each end of the skewer. They should try both equal-sized masses, and unevenly-sized masses during their experimentation. They should then make sure the masses are balanced i.e. the skewer is horizontal.
For the masses supported by a post they should find the appropriate hole to put the pin through. For the masses supported by string they can slide the string along the skewer until the balance point is found.
Once the masses are balanced, they can be spun slowly around each other.
Students should note the path that each mass takes and the size of its orbit. For the mass on a post, a flashlight can be shone from a fixed point above the spinning masses, and the path of their shadows traced on the paper.
Students may also look at how fast each of the masses move, but the size of the orbit is the most important.

They should find that the masses both orbit around the balance point (a small mass does not orbit around a stationary large mass, but they both move around another point).
They should find that with unequal masses, the smaller mass has a larger orbit (and moves much faster) than the larger mass.

Astronomers study couple orbits to discover new objects in the universe. If they find a star in orbit with an invisible companion, they can measure the size and speed of the star's orbit to figure out the size of the invisible companion, and therefore what it might be.
If a star is discovered moving in a large orbit around "nothing", the invisible companion may be a (relatively massive) black hole. The black hole has a huge mass which moves very little, while the orbiting star moves in a large, fast orbit around it. The more massive the black hole, the larger and faster the orbit of the star. In the students' model, their large mass is the black hole and their small mass is the star.
If a star is found to be moving in a small orbit (which will be seen as a "wobble" back and forth), the invisible companion may be a (relatively small) exoplanet with a large orbit around the star, that is too small to see itself. In the students' model, their large mass is the star and their small mass is the exoplanet.
(The wobble of a far away star is measured by reading its Doppler shift as it moves away from and towards us.)

Note that with coupled orbits, both masses orbit around a separate balance point, or centre of mass, called a "barycentre". If one mass is a lot larger than the other the barycentre may be within the large object, but it will not be at its centre. The large mass will still make a (small) orbit itself. For simulations of coupled orbits see the gallery near the bottom of https://en.wikipedia.org/wiki/Barycenter
More information on barycentres and discovering exoplanets: https://spaceplace.nasa.gov/barycenter/en/

Coupled orbits can have more than two objects - our solar system is the coupled orbits of the sun, the planets and other bodies that orbit the sun.
Technically, solar system objects, including Earth, are not orbiting the sun, but the sun and all the masses in the solar system orbit the barycentre of the solar system (which is sometimes outside the surface of the sun and sometimes near the centre of the sun). Try this link for the orbit path of the sun around the solar system barycentre:
https://www.researchgate.net/figure/The-orbit-of-the-centre-of-the-Sun-…

Astronomers are searching for "Planet 9" to explain the orbits of the trans-Neptunian objects (objects orbiting the sun beyond Neptune). The apparent location of the barycentre of the solar system cannot be explained by the known objects orbiting the sun, so astronomers are searching for another mass in orbit.
Try Wikipedia entry on Planet 9 for image: https://en.wikipedia.org/wiki/Planet_Nine#/media/File:TNO-Planet9-Diagr…
See NASA webpage on Planet 9 for more information: https://solarsystem.nasa.gov/planets/planetx/indepth

One line summary: astronomers use the phenomenon of coupled orbits to discover black holes, exoplanets and new planets in our solar system.

Before the lesson:
Buy cheap wine glasses. Knock the base off them by tapping the stem just above the base with a metal file or other long, heavy object. Sand down the sharp edges.
Alternatively, use an intact wine glass, but be careful about breakages in the classroom.

Hand out wine glass base lenses, and optionally, other cut glass objects that bend light into interesting patterns.
Hand out paper with printed geometric designs (attachment), and coloured markers for students to make their own designs.
Ask students to move the lenses over the designs and notice how the lenses bend images.
Challenge them to specifically make a circle from a dot. If they need help: slide the wine glass base over the dot until the stem is directly above it, when the dot changes to an arc then a circle.

The wine glass base models how gravitational lensing works. When the wine glass lens is run over a dot, the light from the dot is bent by the lens, so our eyes above the wine class see a circle.
In the same way, astronomers use their telescopes to look for rings of light to discover dense masses in the universe, which can bend light around them. When light from a far away galaxy passes through a nearer black hole or cluster of galaxies, their immense gravity bends the light around them, so that the light that reaches our telescopes appears as an arc, or even a circle.
Try these webpages for images of gravitational lensing of light around black holes or galaxies: https://en.wikipedia.org/wiki/Einstein_ring http://static.ddmcdn.com/gif/blogs/6a00d8341bf67c53ef01630128de99970d-8…

Gravitational lensing images provide information on several astronomical phenomena:
They can be used to map where black holes are.
They can be used to map the dark matter in the universe, which cannot be seen but has enough mass to bend light.
Dark energy existence has been supported by gravitational lensing images.
Cosmic microwave background radiation is also bent by gravitational lensing, so is studied this way.
Galaxy clusters can be weighed with from gravitational lensing images, as the amount of lensing depends on the mass.
Early universe galaxies can be seen and studied with gravitational lensing, which magnifies light images (lensing arc image).

If no tornado connector is available:
Drill out the centre of the caps, then hot glue them together face to face, without sealing over the hole. More hot glue and duct tape will be needed to minimize leaks from the bottles during the activity. Have a towel ready.

Fill one of the bottles with water two thirds full.
Add the optional floating bits.
Add the tornado connector, or the home-made connector, before screwing on the other bottle.

Turn the bottles upside down so that the water is in the upper bottle, hold the bottles tightly at the join and rotate in a large circle to initiate a tornado of water down into the lower bottle. The floating bits will help visualize the rotation of the water through the tornado.

This activity can be used to model several real phenomena including:
1. Black hole accretion discs: the cloud of gas and dust swirling around a black hole form a spinning "accretion disc". Long streamers of gas are pulled into the black hole by gravity, travelling faster as they are pulled in. Although a black hole itself is not visible, the accretion disc around it is.
2. Tornadoes, hurricanes and waterspouts - although note that these swirl upwards not downwards.

Assembling the spectroscope:

Flatten a cereal box.
Image 1:
Draw panels so that the cereal box can be folded into a square tube, using the folds already present (side panels of cereal box may become one or two sides of the spectroscope).
Score folding lines, on the outside of the fold (printed side of the box) all the way across the box. (The brown inside of the box will end up on the inside of the tube, as it is darker and will reflect less light.) Cut all the way through the cardboard when you reach the end tabs.
Cut end tabs at one end of the cereal box, so that they can fold down to close the end (the length depends on the size of the cereal box). Cut off one of the middle tabs, and on same panel, cut a hole (4-5.5cm from end and 1cm wide). This viewing hole is on “the top” of the spectroscope.
Cut the tabs at the other end of the cereal box, so that they fold in to make a narrow slit, 1mm wide, across the box.
Image 2: tabs folded to show the slit (this will be folded last in the assembly)
Fold the cardboard into a tube and tape the long side with duct tape or masking tape. It can be easier to put short pieces of tape in a couple of places first to align the edges before adding the long strip. Tape the flaps closed, leaving the top edge open near the viewing hole.
Image 3:
From the opening near the viewing hole, measure a 60 degree angle from the vertical, on both sides, and mark a line at this angle in pencil.
Image 4:
Cut slits 4cm long along this line. Alternatively, these slits can be cut in the cardboard ahead of time for the students.
Cut a DVD in half (or quarters with smaller cereal boxes) with sharp scissors (less likely that the layers will separate than trying to snap it). Insert the DVD piece into the 60 degree slit, making sure the recordable side (with the grooves) is up.
Check the spectrum is visible before taping the DVD in place: point the slit directly at a light source, then look through the hole at the reflection of the light off the DVD.

Using the spectroscope to look at different light sources:

The spectroscope separates the colours of light. They are seen as a "spectrum".
Students can look at various bulbs in the classroom to see what kinds of spectra they have. Or field trip: visit the local stores and look at their various lights through the spectroscope, to find out what kind they are (a supermarket has a god selection of lights with the fridges, displays and overhead lighting.
Primaries can look for different kinds of spectra (broken or continuous) and the colours (see primary worksheet attached). Intermediates can be challenged to find their own patterns in the spectra.

Expected results:
Viewing an incandescent or LED bulb with the spectroscope will show a continuous spectrum - the colours are all smeared together. Every wavelength of light is emitted by these bulbs. See image 8. LED bulbs of one colour will have continuous spectra within these colours.
A fluorescent bulb will show distinct lines of colour - a broken spectrum. The colour of the lines present depend on the gases inside the fluorescent bulb (often mercury and argon). The lines are made as the different gases emit light of certain wavelengths. See image 9.

Additional activity to show sodium emission line:
A candle will give a continuous spectrum. Throw a little salt in the candle and a yellow line will flare up. The sodium in the salt emits light of this yellow wavelength when it is excited (by the heat of the candle). As the sodium atoms lose energy again they emit it as light of this particular wavelength.

Viewing the sun's spectrum:
Take the students outside to view the sun's spectrum with their spectroscope. DO NOT allow students to look directly at the sun. Ideally they point at light clouds in the other direction from the sun, or the blue sky.
They will see that the sun's light makes a continuous spectrum, so emits all wavelengths of light.
If they are lucky they will see Fraunhofer lines - dark lines crossing the spectrum that are the result of gases in the sun (and also the earth's atmosphere) absorbing certain frequencies of light. Try links for images of Fraunhofer lines in sun's spectrum: https://media1.britannica.com/eb-media/02/96902-004-856CCB82.jpg or http://jazzistentialism.com/blog/wp-content/uploads/2014/05/fraunhoferl… Scientists look at the position of these dark lines to deduce what molecules our sun is made of. Ask students where they see the lines and tell them what molecules in the sun's atmosphere they are detecting.

Extension with Fraunhofer lines for older students:
The position of the dark lines tell astronomers what other stars are made of and what type of star they are looking at: http://www.cnyo.org/wp-content/uploads/2014/02/2014feb26_WhiteDwarf.jpg
The lines also tell them how fast and in what direction the stars are moving, by how red-shifted the lines are. Red-shift image try http://en.wikipedia.org/wiki/Doppler_effect#mediaviewer/File:Redshift.s…. See Doppler effect activity to model how red-shift works using sound.

This activity taken from Society of Physics Students outreach manual: https://www.spsnational.org/sites/default/files/files/programs/2012/soc…

Tell students they will be using the gravity well to model the shapes and speeds of orbiting objects. They release their marble so that it orbits the centre well of the fabric. The centre well models the gravity of the sun/a star/a black hole (depending on the emphasis of the lesson). Their marble may model a planet, dwarf planet, asteroid, comet orbiting a star. Or their marble can model a star orbiting a black hole.
(See below for comments on how this model is different from real astronomical objects in orbit.)

As students experiment, prompt them to notice the shapes of the orbits they make, and maybe also the speed of the marble at different distances from the well.

Discussion on orbit shapes
Ask students what shaped orbits they made, and compare their descriptions to orbit shapes of astronomical objects. Our familiar planets have a circular orbit, whereas comets and several trans-Neptunian dwarf planets have elliptical orbits.
Show images of various orbits (of planets, moons, dwarf planets, asteroids, Kuiper belt objects and comets), during experimentation or after.
Try this image for comet orbits: http://www.wired.com/images_blogs/wiredscience/2013/08/Orbits_of_period…
Try this page for images for orbits of dwarf planets in the solar system, to give a sense of how many objects orbit the sun: http://www.duncansteel.com/archives/2140 or do an image search of "orbit Eris Haumea Makemake").
Discussion on why objects orbit: they are continually "falling" towards the sun, or central gravity well, but as they are in forward motion, they never reach it, but instead curve around it.
Note on why our planets' have a circular orbit: maybe because they were formed from a spinning disc of debris, so all end up in the same plane. Also, if they were not circular, we would not be here to observe them! (Our distance from the sun would change a lot, making a challenge for life to survive.)

Kindergarteners and young primaries can draw the shapes they made with their marble: circle, elipse, long narrow elipse, star shape as the ellipses cycle round. Orbits in the galaxy are all these shapes.

Several marbles orbiting at once can represent the asteroid belt, with collisions that knock some of them out of orbit.

Using the gravity well to model stars orbiting a black hole
Stars orbit black holes, so astronomers look for stars that appear to be orbiting around "nothing", as evidence for the presence of a black hole. By mapping the locations of all objects in orbit, the location and size of the black hole can be calculated.
Show students an image of star orbits around a black hole. Try this image, or search images for "SgrA* orbits": https://inspirehep.net/record/800608/files/f16.png
To modify the gravity well model to be more like the shape of the gravity well of a black hole, add a ring underneath to model the event horizon (the point past which nothing can escape from a black hole's gravity). See the last two photos.

Discussion about orbit speeds
Ask students to notice what happens to the speed of an orbit as the object approaches the gravity well of the sun, as astronomical objects behave the same. They speed up near the object they are orbiting, gaining kinetic energy. As they move outwards they lose speed, but gain another kind of energy - gravitational potential energy. (Similar to a ball been thrown in the air or a roller coaster ride.) Planets with large orbits spend most of their time far from the sun, where they are moving more slowly.
Our solar system is orbiting the centre of our Milky Way galaxy, with average velocity of 720,000km.hr!
A black hole has an event horizon, past which the object cannot escape its gravity, however much energy it has.

Using the gravity well to model how the moon causes tides

Information on classes of objects that orbit the sun
Planets - now 8 planets, as Pluto is now classified as a dwarf planet. To be a planet, an object needs to 1. be massive enough to pull itself into a sphere under its own gravity 2. is not massive enough to cause thermonuclear fusion (like a star) and 3. has cleared its neighbouring region of smaller objects i.e. they are attracted by its gravity.
Dwarf planets - large enough to be spherical, but too small to clear their neighbourhood of smaller objects. There are many many dwarf planets orbiting the sun, and more are continuously being discovered. Examples: Ceres in the asteroid belt, Trans Neptunian objects (TNOs) such as Pluto, Eris, Makemake, Haumea.
Asteroids - small irregularly shaped objects made of rock, metal or a mixture of both, found in the asteroid belt. Image of main asteroid belt at: http://www.rawscience.tv/wp-content/uploads/2014/09/asteroid-belt.jpg
Comets - snowballs of frozen gases, rock and dust the size of a small town. A comet warms up near the sun and develops a coma (atmosphere), a glowing head, hundreds of thousands of km across. It has two tails (which always point away from sun), one gas and one dust (which curves with sun’s gravity). Image of comet structure through its orbit: http://www.skyandtelescope.com/wp-content/uploads/Koehn_IZ_orbit_300dpi… Comets may have brought water and organic compounds (the building blocks of life) to Earth and other bodies in our solar system. There are billions of them. Image of some comet orbits at: http://www.wired.com/images_blogs/wiredscience/2013/08/Orbits_of_period… (Orbit times: Halley orbit is 76 years, Borrelly orbit is 7 years, Ikeya–Zhang orbit is 366 years and is the longest known orbital period.)

Differences between this gravity well and real orbiting objects
Ask older students for ideas in how their model is different from real orbiting objects at the end of this activity.
In this model, every marble inevitably loses energy to friction as it rubs against the cloth and falls into the gravity well. In the vacuum of space there is no friction, and orbit shapes are maintained, as long as there are no collisions.
Physicists use this kinds of model of gravity, though they would use mathematics to describe the shape of a gravity well, rather than a physical object. The more massive the body, the deeper and more extensive the gravity well associated with it. Black hole has a very deep well.

Activity adapted from: http://mars.nasa.gov/education/modules/GS/GS38-49.pdf, see also https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf

Introduce the activity:
In the solar system, chunks of rock orbiting the sun, can collide with planets or moons.
(The asteroids, small chunks of rock and metal, are mostly concentrated in the asteroid belt, between Mars and Jupiter, but a collision between them sends an asteroid out of the asteroid belt where they might collide with planets or moons. Image of asteroids: https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg)
Impact craters, from when a "meteoroid" hits the surface, are the dominant geographic features on many solid Solar System objects. (Early in the history of our solar system, asteroid impacts were much more common. Now, many of these stray chunks of rock have been caught by the gravity of big planets.)

Shake a tray of flour back and forth so that the surface of the flour is relatively flat. Do not press the surface down - allow it to settle with its own weight.
Sprinkle cinnamon over the flour to make an even coat of brown over the flour.
Optionally ask students to make asteroid-shaped pieces with their modelling clay. (Show them shapes from here: https://en.wikipedia.org/wiki/Asteroid#/media/File:Asteroidsscale.jpg)
Allow students to drop the marble/clay ball from a height above the tray.

Name the parts of the crater that are formed (either in the introduction or while circulating around the classroom when students are working):
The floor of the crater (the bottom of the hole), the rim (the raised edges ringing the hole), ejecta (material projected out of the crater - it will look white in contrast to the brown cinnamon), rays (long lines extending away from the crater; a pattern made by the ejecta).
(See p.3 of Activity adapted from: https://www.nasa.gov/wp-content/uploads/2009/07/impact-craters.pdf)

Ask students to try dropping the asteroid from different heights (therefore different impact speed), and to observe the difference in the crater pattern made.
Optional: ask students to measure the heights they are dropping from and to measure the diameter of the crater from rim to rim in each case. (Note that this data is messy and there is not a huge amount of difference between high and low drop heights, but it demonstrates graphing data, and how to draw lines of best fit. See worksheet attached.)

Ask students to try dropping their asteroid onto a tray that is angled, to model an asteroid impacting a planet surface at an angle.

Show students how to stir up the flour and cinnamon to make an even colour then reapply the cinnamon. They will need to do this when there are several craters in their tray, and it gets hard to see the patterns.

Discussion points:
1. Students should find that the crater diameter is always larger than the asteroid. When the surface of a real planet or moon is hit by a chunk of rock (more precisely called a meteoroid, or the "impactor"), the shock fractures the surface rock and makes a large cavity which is larger than the impactor. The impact sprays material ("ejecta") in all directions. (Any remaining rock pieces are called meteorites.) Asteroids hit the moon at an average of 20 kilometers per second, and make a crater 10 t0 20 times larger than the impacting object.
2. Point out to students that the marble/clay stays in the hole - for a real crater the impact rock has gone. It has shattered and been distributed with the ejecta. Or if the impact generates enough heat, the impactor melts or vapourizes.
3. Either through eye-ballng the difference in patterns, or by graphing data collected, the size of the crater and the average ray length increases with impact speed. (See graph of data - it is messy, but a line of best fit shows the trend.)
Show students an image of real craters and ask if theirs looked similar e.g. on Mercury: http://photojournal.jpl.nasa.gov/jpegMod/PIA11355_modest.jpg and on the Moon: https://myearthscience.com/wp-content/uploads/2017/11/crater-rays-moon…. Next time students see a full moon, they might be able to find the crater rays on it: https://upload.wikimedia.org/wikipedia/commons/2/2d/Full_Moon_%28159847…
Tell students that scientists work the other way around: they can figure out the speed of an impact by the size of the crater formed. They also look at other features that are made with the very high speeds of meteorites hitting moons and planets - sometimes craters have central uplifts and terraced walls that give more information about the impact and the rock on and under the surface of the planet.
4. If relevant, ask students what patterns they got from an angled impact, and compare to a real "oblique impact": http://lroc.sese.asu.edu/posts/595
5. Show students a crater with different features - Rampart Craters on Mars (https://en.wikipedia.org/wiki/Rampart_crater). There are no rays. Water or ice present under the impact site melted with the impact, then flowed away instead of being thrown away from the crater. This pattern of ejected material can be used as a way to identify areas with possible water or ice in the surface layers of a planet.

The number of craters on a surface can tell scientists about a planet:
Many craters indicate that there is no atmosphere to burn up the rocks as they come down. (e.g Mercury). It also may indicate that there are no plate tectonic movements or erosion turning over the planet’s surface. Earth and Venus have an atmosphere, which burns up rocks as they hit it (called "meteors" or "shooting stars"). Earth also has moving tectonic plates and erosion that recycle the rocks, so removing craters. (The craters on the Moon are good for studying crater formation, as the Moon has no atmosphere, plate tectonics, or moving water (which all erode a surface and erase all but the most recent impacts).
http://mars.nasa.gov/education/modules/GS/GS38-49.pdf