Chapter 17

Here’s Chapter 17 – Comets, Meteors and Meteorites. Again, if there’s anything that might look a bit wrong, let me know!  😀

1. a) If you see an object moving quickly across the sky, can it be a comet? If not, why?
A fast moving object in the night sky will not be a comet; this is because the distance between Earth and the comet is so great, any movement detected from a comet would take hours to occur. If you do see something moving quickly across the sky, it is most likely a satellite.

1. b) Why does a comet’s tail point more or less away from the Sun?
The force of the Sun’s activity (mainly Solar Winds) pushes the evaporating materials backwards, away from the origin. Even when the comet is moving away from the Sun, the tail is pointing away from the Sun; making the comet look like it’s going backwards.

1. c) Name the bright comet 1997.
The comet is called Comet Hale-Bopp.

2. a) How was Edmond Halley able to show that the comet of 1682 was periodical?
He looked back at past records of comets, and saw that there were a series of comets that shared the same movement pattern as the one in 1682. He estimated that the comet took around 76 years to come back to perihelion and predicted that the comet would been seen again in 1785; which is was on Christmas Eve 1785.

2. b) Is the period of Halley’s Comet exactly 76 years? If not, why?
The period cannot be exactly 76 years because there are different factors which change during each orbit. The positions of the planets and their gravitational fields can adjust the length of the period.

2. c) Generally speaking, why are comets such as those of 1811 and 1843 brighter than periodical comets such as Encke’s?
The comets of 1811 and 1843 are brighter because they have longer periods of orbit than periodical comets. At each perihelion, a comet loses some of its mass; meaning the more often a comet passes the Sun, it loses it’s mass more quickly. That’s why the comets of 1811 and 1843 are brighter, because they haven’t lost as much of their mass.
3. a) Describe the main features of a great comet.
A great comet will have a nucleus of about 25 km across. Surrounding the nucleus will be a bright coma. It is usually this and the tail which is seen at night. The tail is particles that have been evaporated as the comet comes closer to the Sun, and are then blown back away from the Sun by the solar winds.
3. b) How are comets related to meteor streams?
There is a link between comets and meteors. When a comet loses some of its mass, the particles just exist in Space. When a planet, such as the Earth comes along, these small particles rub against the atmosphere and cause friction and heat. They eventually heat up enough so they burn away.

3. c) In what ways do the orbits of most comets differ so strongly from those of planets?
The orbits vary in shape and angle. All the planets in this solar system are arranged in a flat plane, with everything on the same level. However, comets are at an angle to that plane; and enter from above or below, going through the plane. Comets also have very ecliptic orbits, meaning they travel in more of an oval than a circle.
Meteor Radiant
4. a) Explain, with a diagram, why the meteors of any particular shower seem  to issue from a well-marked radiant point.
Think of a motorway, and think of how the lanes all converge on the horizon. This is the same with the meteors. They are all in parallel lines as well, and when they hit the Earth’s atmosphere, they act like cars on the motorway.

4. b) What are sporadic meteors?
These are meteors which can just appear from space, without having any connection with comets or other celestial bodies we have in our solar system.

4. c) What is the difference between a meteor and a meteorite?
The difference is quite simple. A meteor is related to comets, and are generally very, very small. A meteorite is related to asteroids, and these are a lot bigger than a meteor; another way to describe a meteorite is to say it’s a very small asteroid.


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