Unit 6: Astronomy Lecture Notes

Vocabulary flashcards covering the key concepts of Unit 6 Astronomy including planetary motion, stellar evolution, and light physics.

Light-year (ly)

An astronomical unit of distance representing the total distance that light travels in one year.

Astronomical Unit (AU)

A unit of measurement equal to the average distance between the Earth and the Sun, approximately $1.496 \times 10^8\,km$.

Terrestrial Planets

The group of four planets consisting of Mercury, Venus, Earth, and Mars.

Jupiter

The largest planet in the solar system, composed primarily of hydrogen and helium.

Parallax Angle

A measurement, often in arcseconds, used to determine the distance to a star based on its apparent shift against background objects.

Angular Size

The angle that an object subtends at the eye of the observer, used in conjunction with distance to calculate the physical radius of a planet or moon.

Kepler’s First Law

The Law of Orbits, stating that all planets move in elliptical orbits with the Sun at one focus.

Kepler’s Second Law

The Law of Areas, stating that a line connecting a planet to the Sun sweeps out equal areas in equal time intervals.

Kepler’s Third Law

The Law of Periods, stating that the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit ($P^2 \propto a^3$).

Newton’s Law of Universal Gravitation

States that the gravitational force is directly proportional to the mass of the objects and decreases as the distance between the objects increases.

Protostar

An early stage of stellar evolution where nuclear fusion is not yet occurring because internal temperatures and pressures have not reached the required threshold.

Red Giant Phase

The stage of stellar evolution the Sun will enter when it exhausts its hydrogen fuel, leading to expansion.

Upper Right HR Diagram Stars

Gigantic, luminous, and cool stars (Giants and Supergiants) that are relatively uncommon compared to other star types.

Photon Energy ($E$)

The energy of a single particle of light, calculated using the formula $E = hf$, where $h$ is Planck's constant and $f$ is frequency.

Frequency ($f$)

The number of wave cycles that pass a point per unit time, measured in Hertz ($Hz$); for light, it is calculated as $f = \frac{c}{\lambda}$.

Wavelength ($\lambda$)

The distance between successive crests of a wave, typically measured in meters ($m$) for light calculations.