The Universe and the Stars

Astronomical Unit (AU)

The average distance from the Earth to the Sun, roughly 150 million kilometers.

When do astronomers use Astronomical Units (AU)?

To measure distances inside our Solar System.

Light

Year (ly)

Is a light

year a unit of time or distance?

When do astronomers use light

years?

Who discovered the 3 fundamental Laws of Planetary Motion?

Johannes Kepler

How do planets orbit the Sun according to Kepler's First Law?

In ellipses, with the Sun sitting at exactly one focus.

Perihelion

The point in a planet's orbit where it is closest to the Sun and travels at its fastest speed.

Aphelion

The point in a planet's orbit where it is furthest from the Sun and travels at its slowest speed.

What trend is established by Kepler's Third Law (Harmonic Law)?

The larger a planet's orbit, the longer it takes to complete a single revolution around the Sun.

What are the 2 types of planets in our solar system?

Terrestrial (Rocky) and Jovian (Gas and Ice Giants)

What are the characteristics of terrestrial planets?

They are small, dense, rocky, metallic, have few

Which planets are classified as terrestrial?

Mercury, Venus, Earth, and Mars.

What are the characteristics of Jovian planets?

They are massive, made of gas and ice, have many moons, possess ring systems, and sit outside the Asteroid Belt.

Which planets are classified as Jovian?

Jupiter, Saturn, Uranus, and Neptune.

the absolute rule that dictates a star's entire lifecycle

Mass is destiny. Its initial mass at birth.

What is hydrostatic equilibrium in a star?

The stable balance between the inward crush of gravity and the outward push of thermal radiation pressure from nuclear fusion.

What nuclear reaction occurs in the core of a main

sequence star?

What neighborhood on the H

R Diagram contains stable, healthy stars undergoing hydrogen fusion?

What are the five lifecycle stages of an average/low

mass star like our Sun?

What are the five lifecycle stages of a high

mass star?

What is a planetary nebula?

A glowing ring of gas shed by a dying, low

What do the vertical and horizontal axes of an H

R Diagram measure?

What is unique about the temperature scale on an H

R Diagram?

Why are stars in the Giant neighborhood of the H

R Diagram highly luminous despite being cool?

What is a White Dwarf?

A tiny, earth

What is a spiral galaxy?

A flat, spinning, pinwheel

What is a barred spiral galaxy?

A subtype of spiral galaxy where stars in the center form a linear bar, with spiral arms trailing off the ends.

What type of galaxy is the Milky Way?

A barred spiral galaxy.

What is an elliptical galaxy?

A smooth, football

What is an irregular galaxy?

A symmetrical splatter

What is escape velocity?

The minimum speed required to permanently escape the gravitational pull of a celestial body.

What is a black hole singularity?

An infinitely tiny point where a massive star's worth of matter is compressed, creating intense gravity.

What is the event horizon of a black hole?

The imaginary boundary where the escape velocity exactly equals the speed of light, making escape impossible.

What did Edwin Hubble discover about the universe by observing distant galaxies?

The fabric of space is actively stretching and expanding every second.

What is cosmological redshift?

The stretching of light waves toward longer, redder wavelengths as a galaxy moves away from the observer.

What is cosmological blueshift?

The compressing of light waves toward shorter, bluer wavelengths as an object moves toward the observer.

What is normal (baryonic) matter?

Ordinary matter made of atoms that makes up stars, planets, and humans, accounting for only about 5% of the universe.

What is dark matter?

An invisible form of matter that does not interact with light but exerts a gravitational pull that holds fast

What is dark energy?

An invisible force permeating space that acts as "anti

What is the functional difference between dark matter and dark energy?

Dark matter pulls structures together via gravity, while dark energy pushes the universe apart.