SPACE

6. How much matter something contains.
7. Forms after a star has run out of hydrogen fuel for nuclear fusion, and has begun the process of dying.
11. The complete range of all types of radiation that has both electric and magnetic fields and travels in waves.
15. Formed when a massive star runs out of fuel and collapses.
16. The force by which a planet or other body draws objects toward its center.
18. The explosion of a star.
20. Gaseous cloud from which, in the so-called nebular hypothesis of the origin of the solar system, the Sun and planets formed by condensation.
21. Very bright, distant and active supermassive black holes that are millions to billions of times the mass of the Sun.
22. A group of stars that appears to form a pattern or picture.
23. Small, rocky objects that orbit the Sun.
24. The stellar core left behind after a dying star has exhausted its nuclear fuel and expelled its outer layers to form a planetary nebula.
25. Graph in which the absolute magnitudes (intrinsic brightness) of stars are plotted against their spectral types (temperatures).

1. Brightest star in the night sky.
2. How bright an object appears in the sky from Earth.
3. The angle between the Earth at one time of year, and the Earth six months later, as measured from a nearby star.
4. Pair of stars in orbit around their common center of gravity.
5. The force by which a planet or other body draws objects toward its center.
8. A dense central bulge lies at the center of a rotating disc, which features a spiral structure that originates at the bulge.
9. Looks like a star but its core is not yet hot enough for fusion to take place.
10. A measure of its resistance to a change in the state of its motion.
12. The apparent magnitude an object would have if it were located at a distance of 10 parsecs.
13. A streak of light in the sky caused by a meteoroid crashing through Earth's atmosphere.
14. Rotating neutron stars observed to have pulses of radiation at very regular intervals that typically range from milliseconds to seconds.
17. Two light nuclei merge to form a single heavier nucleus.
19. Formed when a massive star runs out of fuel and collapses.