Astronomy Key Terms

Across

2. the totality of all matter, energy and space.
4. an object so dense that even light cannot escape from its surface because of the object's intense gravitational field.
5. the distance to a star when the star exhibits a parallax of one second of arc, where 1 second of arc is defined to be 1/3600 of 1°, this distance is equal to 3.26 light-years or 206 265 astronomical units.
9. ..... planets, a new class of planets including Pluto, Ceres, Eris, Haumea, and Makemake.
11. imaginary lines encircling the Earth parallel to the plane of the equator.
12. Sun's outer solar atmosphere, can be seen as a halo extending beyond the solar disk, especially during solar eclipse
15. large and small chunks of matter that orbit the Sun (usually between Mars and Jupiter within "asteroid belt"), sometimes called minor planets.
17. the blocking of light of one celestial body by another.
18. prominent groups of stars appearing as patterns in each section of the night sky.
20. ........ coordinate system, a two-dimensional coordinate system in which two number lines (x,y) are drawn perpendicular to each other and the origin is assigned at the point of intersection, a third dimension may be taken in the z direction, perpendicular to x and y.
21. the apparent sphere of the sky on which all the stars seems to appear.
24. a relatively small object that is composed of dust and ice and that revolves about the Sun in a highly elliptical orbit.
28. layer of the Sun surface above the photosphere.
31. the movement of one object around another.
32. an imaginary line on the Earth's surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere.

Down

1. unit of length used informally to express astronomical distances; it is approximately 10 trillion km (6 trillion miles); it is distance that light travels in vacuum in one Julian year; 1 light-year = 9.461 trillion km = 5.878 trillion miles = 63 241 au
3. an exploding star.
4. theory of the beginning of the universe that states that the known universe was smaller, hotter and denser in the past, and that it began rapidly expanding 13.7 billion years ago.
6. a doughnut-shaped ring of space around the Sun beyond the orbit of Neptune and that extends to well beyond the orbit of Pluto and Eris, containing many short-period comets.
7. the fraction of incident sunlight reflected by a celestial object.
8. an extremely large collection of stars bound together by mutual gravitational attraction, have a spiral, elliptical or irregular structures.
10. ..... planets, the four outer planets of the solar system - Jupiter, Saturn, Uranus and Neptune, all have charcteristics resembling those of Jupiter, having gaseous outer layers.
13. ..... planets, the four inner planets of the solar system - Mercury, Venus, Earth, and Mars, all are similar to the Earth in general chemical and physical properties.
14. the average distance between the Earth and the Sun, which is 1.5 x 108 km (93 million miles).
16. model, the old false theory of the solar system, which placed the Earth as its center.
19. angular measurement, in degrees, east or west of the reference meridian, known as the Greenwich (prime) meridian for a point on the surface of the Earth.
22. angular measurement in degrees north or south of the equator for a point on the surface of the Earth.
23. model, the model of the solar system that places the Sun as its center.
25. a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium, an early stage in the process of star formation.
26. the bright, visible "surface" of the Sun.
27. imaginary lines drawn along the surface of the Earth running from the geographic North Pole to the geographic South Pole perpendicular to equator.
29. the turning (spinning) of an object about an internal axis.
30. small, interplanetary metallic and stony objects in space before they encounter the Earth.