# Apologia Physical Science 1st ed.: Module 16

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Definitions and important stuff to know for module 16 (entitled 'An Introduction to Astrophysics') of the first edition of Apologia's 'Exploring Creation with Physical Science', by Dr. Jay Wile. When studying any of my sets, it may be helpful to ignore stuff in parentheses. I have annotated a few extra things, and you don't necessarily need to know my notes to ace the test. Happy studying! -maxacademy

### What are the four layers of the sun, from inside to outside?

core, radiative zone, convection zone, photosphere

### nuclear fusion

the process by which two or more small nuclei fuse to make a bigger nucleus

### nuclear fission

the process by which a large nucleus is split into two smaller nuclei

### critical mass

the amount of isotope necessary to cause a chain reaction

### star magnitude

the brightness of a star on a scale of -8 to +17. The smaller the number, the brighter the star.

### Name the special letters on the Hertzsprung-Russell diagram, in order from hottest temperature to coolest temperature.

O(h), B(e), A, F(ine), G(irl), K(iss), M(e)

### Name the three different types of novas, in order from longest to shortest lifespan.

pulsating variables, novas, supernovas

### What are the two methods astronomers use for measuring distance from Earth to a star?

parallax method (uses geometry), apparent magnitude method (uses Cepheid variables)

### Between the parallax method and apparent magnitude method, which has the most accuracy? And which can be used to measure long distances?

The parallax method is more accurate (because it is purely based on math).
The apparent magnitude method can be used to measure long distances (though it just makes assumptions and is not as accurate as the parallax method).

### light year

the distance light travels in one year (about 587,849,981,000,000,000,000 miles!)

### galaxy

a massive ensemble of hundreds of millions of stars, all interacting through the gravitational force, orbiting around a common centre

### What are the three types of galaxies (in no particular order)? What type of galaxy is the Milky Way?

spiral, lenticular, elliptical.

The Milky Way is a spiral galaxy.

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