Modern Astronomy

What is the distance ladder?

A series of methods used to measure distances in space.

What is parallax?

Measuring nearby star distances using their apparent shift in position.

What is the period-luminosity relationship?

A Cepheid variable star's period reveals its luminosity, helping measure distance.

What is spectroscopic parallax?

Estimating a star's distance using its properties and the H-R diagram.

What does the H-R diagram show?

Stars arranged by luminosity and temperature.

What is the interstellar medium (ISM)?

Gas and dust found between stars.

What are molecular clouds?

Cold, shielded clouds made mostly of molecular hydrogen where stars form.

What radiation does hot ionized gas emit?

Ultraviolet radiation.

How can molecular clouds be observed?

Through infrared and radio emission and absorption.

Why are there dark patches in the Milky Way?

Interstellar dust blocks starlight.

What is a reflection nebula?

A dust cloud reflecting light from nearby stars.

What causes reddening?

Dust scatters blue light more strongly than red light.

What radiation does interstellar dust emit?

Infrared radiation.

What causes a molecular cloud to collapse?

Gravity overcomes gas pressure.

What happens as a molecular cloud contracts?

It spins faster and can break into smaller regions.

Why do stars form in clusters?

Star formation often happens in waves within large clouds.

What is a protostar?

A young star still forming from collapsing gas.

Which is larger and denser: a cloud or a protostar?

The cloud is larger, but the protostar is denser.

What powers a pre-main-sequence star?

Gravitational contraction instead of nuclear fusion.

What clears gas away from a young star?

Stellar winds.

Why do planets form around stars?

Leftover gas and dust form a spinning disk where planets develop.

What is the skater effect?

A contracting spinning object rotates faster.

What is the Doppler method for detecting planets?

Detecting a star's wobble through changes in its spectrum.

What is the transit method for detecting planets?

Detecting a planet when it passes in front of its star and dims its light.

What are selection effects in planet detection?

Some planets are easier to detect than others.

What is a rogue planet?

A planet that does not orbit a star.

What is the Drake Equation?

An equation estimating the number of communicating civilizations in our galaxy.

What does N represent in the Drake Equation?

The number of communicating civilizations.

What does R* represent in the Drake Equation?

The rate of star formation.

What does fp represent in the Drake Equation?

The fraction of stars with planets.

What does ne represent in the Drake Equation?

The average number of potentially habitable planets per planetary system.

What does fl represent in the Drake Equation?

The fraction of habitable planets where life develops.

What does fi represent in the Drake Equation?

The fraction of life-bearing planets where intelligent life develops.

What does fc represent in the Drake Equation?

The fraction of intelligent civilizations that communicate.

What does L represent in the Drake Equation?

How long civilizations remain detectable.

What is the main sequence?

The stage when stars fuse hydrogen into helium in their cores.

Why do stars leave the main sequence?

They run out of hydrogen in their cores.

Why do massive stars have shorter lifetimes?

They burn through their nuclear fuel faster.

What happens when a star becomes a giant?

Its size and luminosity increase greatly.

What does cluster evolution reveal?

Massive stars evolve faster than low-mass stars.

What determines how a star dies?

Its mass.

What happens during helium burning?

Helium fuses into carbon.

What is double-shell burning?

Hydrogen and helium fuse in separate shells around a star's core.

Which stars form planetary nebulae?

Low-mass stars, like the Sun, eject their outer layers.

What happens to the Sun at the end of its life?

It becomes a white dwarf, not a neutron star.

What are the sizes of white dwarfs and neutron stars?

White dwarfs are Earth-sized; neutron stars are city-sized.

What is a white dwarf made of?

Mostly carbon and oxygen, supported by electron pressure.

What is the Chandrasekhar mass limit?

About 1.4 solar masses, the maximum mass for a typical white dwarf.

How does a neutron star form?

A massive star's core collapses, combining protons and electrons into neutrons.

What is a neutron star made of?

Mostly neutrons packed extremely tightly together.

Why is neutron star material denser than white dwarf material?

Neutron stars compress more mass into much less space.

What is a pulsar?

A rotating neutron star whose radiation beams sweep past Earth like a lighthouse.

What is a Type II supernova?

A massive star's iron core collapses, causing an explosion.

What role do neutrinos play in a supernova?

They carry energy away and help power the explosion.

What triggers a Type Ia supernova?

Runaway nuclear burning in a white dwarf.

How does a solar-mass star eject its outer layers?

Late-stage instability and double-shell burning lead to mass loss.

What is an accretion disk?

A spinning disk of matter falling toward a compact object.

What is an event horizon?

The boundary beyond which nothing, including light, can escape.

What is a black hole singularity?

A theoretical point of infinite density at a black hole's center.

What are two ways a black hole can form?

A massive star's core collapses, or a neutron star gains enough mass to collapse.

What is gravitational lensing?

Gravity bending light from distant objects.

What are three pieces of evidence for black holes?

Orbiting stars, X-rays from accretion disks, and gravitational lensing.

What is a quasar?

An extremely bright active galactic nucleus powered by a feeding supermassive black hole.

Why is the sky blue?

Air molecules scatter blue light more strongly than red light.

Why are sunsets red?

Sunlight travels through more atmosphere, scattering away much of the blue light.