stars, galaxies, or celestial bodies

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Across
  1. 1. The time after sunset or before sunrise when the sky is not fully dark. Astronomical twilight ends after sunset (and begins before sunrise) when the Sun is 18° below the horizon.
  2. 4. A telescope’s main light-gathering lens or mirror.
  3. 6. The edge of a celestial object’s visible disk.
  4. 7. The point in the sky that’s directly overhead.
  5. 10. The two times each year, near March 20th and September 22nd, when the Sun is directly overhead at noon as seen from Earth’s equator. On an equinox date, day and night are of equal length.
  6. 11. The distance that light (moving at about 186,000 miles per second) travels in one year, or about 6 trillion miles.
  7. 12. When the Moon or other body appears more than half, but not fully, illuminated (from gibbus, Latin for “hump”).
  8. 13. A small telescope used to aim your main scope at an object in the sky. Finderscopes have low magnifications, wide fields of view, and (usually) crosshairs marking the center of the field.
Down
  1. 2. The angle between the plane of an orbit and a reference plane. For example, NASA satellites typically have orbits inclined 28° to Earth’s equator.
  2. 3. An increase in meteor activity at certain times of the year due to Earth passing through a stream of particles along a comet’s orbit around the Sun.
  3. 5. A star whose brightness changes over the course of days, weeks, months, or years.
  4. 8. The imaginary north-south line that passes directly overhead (through the zenith).
  5. 9. The fraction of the Moon or other body that we see illuminated by sunlight.