Comets

1. The first astronomer to prove that comets are not phenomena within the Earth's atmosphere was

a. Aristotle

b. Hipparchus

c. Tycho Brahe*

d. Kepler

e. Newton

2. Comets are thought to be debris from which the ___ formed.

a. Jovian planets and Pluto*

b. terrestrial planets

c. asteroids

d. meteoroids

e. none of these

3. The orbits of long-period comets are

a. circular

b. in the ecliptic

c. randomly oriented with respect to the ecliptic*

d. similar to Pluto's orbit

e. the same as the orbits of short-period comets.

4. The Oort cloud is located

a. between the orbits of Mars and Jupiter

b. between ~40 –100 AU

c. 1/6 to 1/2 of the way to the nearest star*

d. at nearly the distance to the nearest star

e. somewhere, but we have no idea since it has never been seen!

5. The Kuiper belt is located

a. between the orbits of Mars and Jupiter

b. between ~40 –100 AU*

c. 1/6 to 1/2 of the way to the nearest star

d. at nearly the distance to the nearest star

e. somewhere, but we have no idea since it has never been seen!

6. A cometary nucleus has a diameter of roughly

a. 10 km*

b. 100 km

c. 1,000 km

d. 10,000 km

e. 100,000 km

7. The visible coma of an active comet near the Sun may be as large as

a. 1 km

b. 100 km

c. 1,000 km

d. 10,000 km

e. 100,000 km*

8. Ultraviolet observations of Halley's comet showed that the hydrogen halo surrounding a comet may extend to a distance of

a. 1,000 km

b. 10,000 km

c. 100,000 km

d. 1,000,000 km*

e. 10,000,000 km.

9. Which of the following expressions characterizes the composition of a cometary nucleus?

a. dirty snowball*

b. muddy rock

c. hail stone

d. rain drop

e. sand bank

10. From spacecraft flyby observations, we now know that the nucleus of Halley's Comet is

a. spherical in shape and covered with a light-colored dust

b. spherical in shape and covered with a dark dust

c. irregular in shape and covered with a dark dust *

d. irregular in shape and covered with a light-colored dust

11. The fact that volatile gasses are present in comets today tells us that comets have been

a. subjected to high temperature

b. hot in the past, but are cool today

c. cold in the past, but hot today.

d. cold in the past and still cold today.*

12. Comet tails have been observed to extend to a distance as large as

a. 150,000 km (0.001 A.U.)

b. 1,500,000 km (0.01 A.U.)

c. 15,000,000 km (0.l A.U.)

d. 150,000,000 km (1 A.U.)*

e. 1,500,000,000 km (10 A.U.)

13. The ion tail of a comet always

a. trails behind the head along the orbital path.

b. extends ahead of the head along the orbital path.

c. points toward the sun.

d. points away from the sun.*

e. points perpendicular to the orbital path.

14. The energy that we see as light from a comet comes from

a. Nuclear burning in the core or nucleus.

b. From the heat of vaporization of the gas and dust.

c. From the heat of sublimation of the gas and dust.

d. From gravitational collapse.

e. None of these.*

15. Why was the large cloud of hydrogen that surrounds the head of a comet not detected until 1970.
Because it is only visible in

a. the ultraviolet.*

b. the visible.

c. the infrared.

d. the radio spectrum.

e. None of these.

16. Long-period comets are thought to have formed

a. in the Oort cloud where they are today

b. in the inner solar system, where radiation pressure from the Sun pushed them out to their current place in the Oort cloud

c. in the vicinity of Uranus and Neptune from whence gravitational forces moved them to the Oort cloud*

d. in interstellar space where they were captured by the solar system at the distance of the Oort cloud.

17. Short-period comets do not have randomly oriented orbits because

a. they are affected by the sun's gravity.

b. they are affected by the solar wind.

c. they formed in the Kuiper Belt, a belt shaped region in the plane of the solar system.*

d. their orbits are altered by the drag of their tails in the solar wind.

e. they all were originally objects ejected from the asteroid belt.

18. A meteor shower is produced when

a. a large number of sporadic meteors are observed.

b. Earth passes through the asteroid belt.

c. massive particles are carried outward from the sun by the solar wind and enter Earth's atmosphere.

d. Earth passes through the orbital path of a comet. *

e. meteors cause condensation in the upper atmosphere that leads to early morning rains.