GLY 1001 Earth Science Name:___Answers____

Chapter 21 Part K: Key Terms

Fill in the blanks with the word(s) that best fit the description:

1. __ Aphelion ____ – the place in the orbit of a planet where the planet is farthest from the Sun

2. Astronomical unit (AU) – Average distance from the earth to the Sun; 1.5 x 10⁸ km or

93 x 10⁶ miles

3. _ Celestial sphere _– An imaginary hollow sphere upon which the ancients believed the stars were hung and carried around the earth

4. _ Constellations ____ – An apparent group of stars originally names fir mythical characters. The sky is presently divided into 88 of the these groups.

5. __ Declination _____ –The angular distance north or south of the celestial equator denoting the position of a celestial body.

6. __ Ecliptic ______ – The yearly path of the Sun plotted against the background of the stars.

7. Equatorial system – A method of locating stellar objects much like the coordinate system used on the Earth’s surface.

8. Geocentric – The concept of an Earth-centered universe.

9. __ Heliocentric ____ – The view that the Sun is at the center of the solar system.

10. __ Lunar eclipse _____– An eclipse of the moon.

11. _ Mean solar day _– The average time between two passages of the Sun across the local celestial meridian.

12. ___ Perihelion ___ – The point in the orbit of a planet where it is closest to the sun.

13. __ Perturbation ____– The gravitational disturbance of the orbit of one celestial body by another

14. Phases of the moon – The progression of chances in the Moon’s appearance during the month.

15. _ Plane of the ecliptic __- The imaginary plane that connects Earth’s orbit with another celestial sphere

16. __ Precession _____ - A slow motion of Earth’s axis that traces out a cone over a period of 36,000 years

17. Ptolemaic system – An Earth-centered system of the universe.

18. Retrograde motion – The apparent westward motion of the planets with respect to the stars.

19. __ Revolution ____ - The motion of one body about another, as the Earth about the sun.

20. ___ Right ascension __– An angular distance measured eastward along the celestial equation from the vernal equinox

21. ___ Rotation ____ – The spinning of a body such as the Earth, about its axis.

22. Sideral day – The period of Earth’s rotation with respect to the stars.

23. Sideral month – A time period based on the revolution of the Moon around the earth with respect to the stars.

24. __ Solar eclipse ___– An eclipse of the Sun

25. Synodic month – The period of revolution of the Moon with respect to the Sun, or its cycle of phases

Chapter 21 Word List:

Aphelion Astronomical unit Celestial sphere Constellations Declination Ecliptic Equatorial system Geocentric Heliocentric

Lunar eclipse Mean solar day Perihelion Perturbation Phases of the moon Plane of the ecliptic Precession Ptolemaic system Retrograde motion

Revolution Right ascension Rotation Sideral day Sideral month Solar eclipse Synodic month

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