Astrophysics & Deep Space Astronomy Essentials

The boundary surrounding a black hole where the gravitational pull is so strong that the escape velocity exceeds the speed of light. Nothing, not even light, can escape it.

Venus has a runaway greenhouse effect caused by a thick atmosphere of 96% carbon dioxide ($\text{CO}_2$) that traps heat. Mercury has virtually no atmosphere to trap heat.

Meteoroid: In space. Meteor: Burning up in Earth's atmosphere (shooting star). Meteorite: A fragment that successfully hits Earth's ground.

The vertical stretching and horizontal compression of an object falling into a black hole, caused by extreme differences in gravitational pull (tidal forces) on its near and far sides.

It measures distance, not time. It is the distance light travels in one Julian year—approximately 9.46 trillion kilometers (5.88 trillion miles).

The leftover thermal radiation or "echo" from the Big Bang, representing the oldest observable light in the universe (from ~380,000 years after its birth).

Any planet that orbits a star outside of our own solar system.

The orbital region around a star where temperatures are just right for liquid water to exist on a planet's surface—neither too hot nor too cold.

A giant interstellar cloud of dust, hydrogen, helium, and other ionized gases where new stars are often born.

A hypothetical form of matter that does not emit, absorb, or reflect light, making it invisible. It is detected only by its gravitational effects on visible matter.

A mysterious, unknown force that permeates all of space and is causing the expansion of the universe to accelerate over time.

The colossal, powerful explosion of a star that occurs during its last evolutionary stages, often triggered by gravitational collapse.

The distance light travels in one minute—about 18 million kilometers. For context, the Sun is roughly 8.3 light-minutes away from Earth.

A donut-shaped region of icy bodies and dwarf planets (like Pluto) located beyond the orbit of Neptune.

A theoretical, immense spherical shell of icy debris surrounding our solar system, thought to be the source of long-period comets.

The collapsed, incredibly dense core of a massive star that went supernova. A single teaspoon of its material would weigh billions of tons on Earth.

A highly magnetized, rapidly rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles, appearing to "pulse" like a lighthouse.

The unit of measurement used to describe the expansion rate of the universe.

A unit of length roughly equal to the average distance from the Earth to the Sun, which is about 150 million kilometers (93 million miles).

An extremely luminous galactic core powered by a supermassive black hole actively feeding on gas and dust, releasing massive amounts of energy.

When an object's orbital period matches its rotational period, causing the same side to always face the body it orbits (which is why we only ever see one side of the Moon).

The maximum mass ($\approx 1.4$ solar masses) that a stable white dwarf star can have before collapsing into a neutron star or black hole.