Astronomy: The Universe and Galaxies Lecture Flashcards

These vocabulary flashcards cover the fundamental aspects of the universe, galaxy types, cosmic history, and dark matter/energy based on the lecture notes.

The Universe

The sum of all time, space, matter, and energy.

Age of the Universe

$13.8$ billion years.

Age of the Milky Way galaxy

$10$ billion years.

Age of the solar system and Earth

$4.5$ billion years.

Star count in the Milky Way

Over $100$ billion, and perhaps as many as $400$ billion.

Galaxy count in the observable universe

About $100$-$200$ billion galaxies.

Galactic Year

The time it takes for our solar system to travel once around the Milky Way, approximately $225$-$250$ million years.

Cosmic Microwave Background (CMB)

Uniform photons left over from the Big Bang, discovered in 1964, that originate from all directions and all times.

WMAP satellite

The satellite used to create an all-sky map of the CMB from 9 years of observations.

CMB Temperature

The actual temperature is $2.725$ Kelvin, with variations between "hot" (red) and "cold" (blue) regions being only $0.0002$ Kelvin.

Cosmic Inflation

A period of rapid expansion occurring between $10^{-32}$ and $10^{-30}$ seconds after the Big Bang.

Recombination

Occurring at $380,000$ years, this is when ordinary matter particles decoupled from light and the Cosmic Microwave Background was released.

Hubble’s Law

The linear relationship between the recessional velocity and the distance to galaxies, expressed as $v = Hd$.

Redshift

A phenomenon in the spectra of galaxies observed by Hubble and Humason indicating that galaxies are moving away from Earth.

Galactic center

The part of a spiral galaxy that contains a supermassive black hole.

Galactic disk

The plane of the galaxy containing spiral arms, gas, dust, and new stars.

Galactic halo

A spherical distribution of old stars in globular clusters.

Spiral Galaxy Classification (Sa, Sb, Sc)

Classification based on the size of the central bulge and the tightness of spiral arms, ranging from Sa (large bulge, tight arms) to Sc (small bulge, loose arms).

Andromeda Galaxy (M31)

The Milky Way’s nearest large neighbor, classified as an Sa spiral galaxy.

Elliptical Galaxies

Galaxies with no disk or spiral arms and very little cool gas or dust, classified from E0 (spherical) to E7 (elongated).

Lenticular (S0 and SB0) galaxies

Galaxies with a disk and bulge but no spiral arms or interstellar gas, sitting between ellipticals and spirals in classification.

Irregular Galaxies

Galaxies with strange shapes often caused by galactic collisions or bursts of star formation, such as the Magellanic Clouds or The Antennae.

Dark Matter

A substance making up $27\%$ of the universe that pulls things together; it explains high rotation speeds in outer galaxies and gravitational lensing around seemingly empty space.

Dark Energy

A substance making up $68\%$ of the universe that pushes things apart and causes the expansion of the universe to accelerate.

Visible Matter

The matter that makes up only $5\%$ of the composition of the universe.

Milkomeda (Future Elliptical Galaxy)

The resulting galaxy formed about $7$ billion years from now after the collision of the Milky Way and Andromeda galaxies.