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Across 1. The daily changes in the moon's appearance as it is viewed from Earth. 5. A phase of the moon in which almost all of the bright half of the moon faces Earth. 6. The outermost layer of the sun's atmosphere, located above the chromosphere. 9. The eclipse that occurs when the moon passes into Earth's total shadow, or umbra, preventing sunlight from reaching the moon; it occurs only at the full-moon phase. 10. The visible surface of the sun. 12. The study of the universe. 13. The inner layer of the sun's atmosphere, located above the photosphere and below the corona. 16. Areas of higher gravity that exist over lunar maria. 20. The combining of the nuclei of lighter elements to form a heavier element. 22. The force of attraction between any two objects with mass; the strength of the attraction is proportional to their masses and inversely proportional to the distance between them. 23. A state of matter consisting of charged particles - positively charged ions, and negatively charged electrons. 24. A rocky or ice fragment that travels through space. 26. Extensive dark areas on the moon that represent great basins and level plains. 27. The increasing of the visible amount of the moon's illuminated surface, from new moon to full moon.

Down 2. Dark areas on the sun's photosphere that result from variations in the sun's magnetic field. 3. Tiny rock fragments no larger than sand grains that travel through space. 4. The eclipse that occurs when the moon passes between the sun and the Earth and the moon's shadow strikes Earth's surface. 7. A grayish brown mixture of small rock pieces and fine particles that covers the moon. 8. A model of the solar system that has Earth at the center. 10. The area of partial shadow surrounding the darkest part of the shadow of the Earth or moon. 11. A bright streak of shattered rock and dust that radiates from a lunar crater. 14. A constant stream of electrically charged particles that is blown out from the sun in all directions. 15. A model of the solar system that has the sun at its center. 17. A glow in the night sky produced in the upper atmosphere by particles from the solar wind interacting with the Earth's magnetic field. 18. The darkest part of the shadow cast by the moon or by Earth. 19. A bowl-shaped depression on the surface of a moon or a planet, usually caused by the impact of a meteorite. 21. The decreasing of the visible amount of the moon's illuminated surface, from full moon to new moon. 25. A trenchlike valley running through the bedrock of lunar maria, believed to have formed after the cave-in of the roof of a tunnel that had transported lava.