The big bang theory

2. the simplest, lightest, and most abundant chemical element in the universe.
4. the scientific study of everything in the universe outside Earth's atmosphere, including stars, planets, comets, and galaxies.
5. a groundbreaking American astronomer who proved that other galaxies exist outside our own and discovered that the universe is expanding.
10. influential American avant-garde theater director, playwright, and visual artist
13. the "afterglow" or leftover heat from the Big Bang, filling all of space as a faint, uniform microwave signal
16. a massive, gravitationally bound system consisting of stars, stellar remnants, gas, dust, and dark matter.
17. a very light, colorless, and odorless gas that is commonly used to make balloons float.
18. German-born theoretical physicist recognized as one of the most influential scientists in history

1. German-born American physicist and radio astronomer
3. famous British astronomer and mathematician who explained how elements (like carbon) are created inside stars.
6. The electromagnetic (EM) spectrum is the entire range of all types of light radiation, both visible and invisible, organized by wavelength or frequency
7. everything that exists, encompassing all space, time, matter, and energy.
8. is the segment of the electromagnetic spectrum that the human eye can view
9. the leading explanation for how the universe began
11. an instrument that splits light (or other radiation) into a spectrum—like a rainbow—and records it.
12. the ability to do work or cause change
14. the stretching of light waves from an object (like a star or galaxy) moving away from us, making the light appear redder.
15. the displacement of the spectrum to shorter wavelengths in the light coming from distant celestial objects moving toward the observer