3Fall-7

Outcomes

• Pupils can explain the difference between planetary orbits and cometary orbits
• Pupils can state some numerical facts about the universe

Specification References

• 1.30 recall that the moon orbits the Earth and that some planets also have moons
• 1.32 explain that gravitational force:

– causes the planets to orbit the sun

– causes the moon and artificial satellites to orbit the Earth

– causes comets to orbit the sun

• 1.34 describe how the orbit of a comet differs from that of a planet
• 1.35 recall that the solar system is part of the Milky Way galaxy:

– describe a galaxy as a large collection of billions of stars

– state that the universe is a large collection of billions of galaxies.

Starter

Making a comet. This is a nice fun demo which provides a good approximation (apparently) of a comet. Here is a BBC video showing the process used. It's worth a watch and relatively short.

The method is pretty simple:

1) Add 2 cups of water to a bag (there is lots of water in comets)

2) Add half a cup of dirt and sand to the bag

3) Add a teaspoon of molasus (this represents the organic material in comets)

4) Add a teaspoon of amonia (this represents the inorganic material in comets)

5) The final step is to freeze everything together with a little dry ice (about half a box). Add the dry ice and start to squeeze the bag together making sure that you're wearing gloves (dry ice is cold). Also it's tricky not getting it everywhere so you might want to wear a labcoat or something and have the kids well back.

6)After a little time it should start to come together. Once it feels fairly solid get it out of the bag and viola, a cometry nucleus. The CO2 should sublime in places, and there may be bubbles on the surface. If you're luck you'll get a jet like the guy in the video. Another thing you can do is to use the fan,IR lamp and lamp to illuminate the tail. It won't be much but the kids get an idea anout a comets tail.

Main Body of Lesson

There are a few notes for this lesson about the number of stars in a galaxy and number of galaxies in the universe. These are typical recall questions for exams. There are also some notes on the orbits of the planets and of comets. In the powerpoint there are also some nice pictures of some different galaxies from the Hubble Space Telescope - can lead onto discussion of the benefits of Hubble (could also talk about Hubble's orbit around Earth, the difference between natural and artificial satellites try and go with the interest of the group)

Additional Information

Safety/Hazards

Dry ice is very cold. Use gloves.

Try to avoid splashing the comet concoction