our universe & galaxies

millions or billions of star systems held together by gravity

galaxies

is a spiral galaxy (most common)

The Milky Way

Spiral galaxies

A galactic center with spiraling arms.

• Regular arms thicker towards center

• Barred arms thicker towards ends 

Moving nebulas helps create more stars.

Elliptical Galaxies

Stars concentrate in the center w/o arms as a sphere or lens. Most are smaller; perhaps older galaxies or post-collision structures. 

Less moving nebulas leads to less star creation. 

Irregular Galaxies

A small and uneven spread of stars, with no clustered center. Possibly post-collision leftovers. Examples with & without black holes.

Limited to no new star creation. 

active galaxies

Black holes are massive. Their gravitational pull can hold many stars in orbit. 

 Scientists today think most galaxies have       
    supermassive black holes at their center. 

Constellations

Group(s) of stars that appear to form a pattern in the night sky

Used for navigation and telling time, seasons, religious practices, etc.

Astronomical Unit

The mean average distance between Earth & the Sun

Light-year

Distance light travels over 1 year, about 9.5 trillion km

Parsec

Also known as a parallax second, equal to 3.258 light years

Size

ranges smaller than Earth to x2000 larger than the Sun

Mass

 indirectly observed w/ gravity

Density

varies, larger stars generally less dense

Luminosity

A star’s estimated energy output per second

Nebula

Gravity collapses interstellar gases into smaller and more condensed clumps. 

Masses 20 times bigger than Jupiter will undergo nuclear fusion - the birth of a star.

When a low mass star’s uses up its Hydrogen the core condenses. The outer layer then expands into a-

Red Giant. 

Planetary Nebula

As the Giant Star continues to expand, it loses its outer atmosphere. 

The gasses scatter up to 1 lightyear across before fading over 10,000 years.

White Dwarf

A white dwarf is hotter, but is small with low luminosity as it cools over billions of years.

Protostars with at least 8 times the Sun’s mass can become

Supergiants.

Supernova

Iron (Fe) takes in rather than releases energy. Gravity collapses the core, exploding EM radiation & matter.

Neutron Star l

A massive star’s collapsed core remains after the supernova.

Electrons, neutrons, & protons fuse together. Some neutron stars pulse radiation along its poles as a-

Pulsar

Black Hole

Even more massive stellar cores can collapse into a single point while cycling energy. No matter or energy can escape past the event horizon.