| A | B |
|---|
| solstice | a point in Earth's orbit around the sun where daylight is either the longest or the shortest amount possible |
| equinox | a point in Earth's orbit around the sun where nights and days are the same length |
| lunar eclipse | a darkening of the moon when it passes through Earth's shadow |
| tides | the rise and fall of water in the ocean and seas caused mainly by the gravitational pull of the moon on Earth |
| fusion | the combining of less massive elements to form more massive elements |
| corona | a crown of glowing gases around the sun that can be seen during a total solar eclipse |
| solar eclipse | an alignment of the sun, moon, and Earth where the moon blocks the sun from Earth's view |
| sunspot | a region on the sun of very strong magnetic field |
| solar flare | powerful eruption of very hot gases from the sun |
| aurora | the glow or display of lights in the skies near polar latitudes |
| galaxy | a system of billions of stars, gases, and dust |
| quasars | brilliant objects in space that may be the powerhouses of developing galaxies |
| nebula | cloud of gas and dust in space |
| red giant | a star that has swelled and glows with a red color |
| supernova | the explosion of a star, releasing huge amounts of light and other energy |
| supergiant | like a red giant, the star expands. However, because the star is so massive, fusion continues more steadily and this forms. |
| nova | The red giant collapses as gravity again pulls the outer parts of the star toward the center. Pressure and temperature increase. The outer layers of the star expand to form this. |
| white dwarf | The star in the center of the nova continues to collapse. It becomes a hot, dense, white star called this. |
| black dwarf | When a white dwarf uses up its energy, it becomes a dark, dense star that no longer shines. |
| black hole | an invisible object in space whose mass and gravitational force is so great that not even light can escape. |
| big bang theory | the idea that the universe started when matter exploded about 15 billion years ago. |
| red shift | the change of light waves from retreating objects to the red end of the spectrum. |
