Understanding Stars and the Universe: Key Concepts

Hertzsprung-Russell diagram (H-R Diagram)

A plot of temperature versus color.

Blue star

Hotter and larger than our Sun.

Main-sequence star stability

Expected to be stable for approximately 10 billion years.

Red star

Colder and smaller than our Sun.

Balance for a main sequence star

Achieved when gravitational collapse matches gas pressure.

Red shifts in spectral lines

Indicate that the universe is expanding.

Cool stars evolution

False; cool stars evolve much more slowly than hot stars.

Dark Energy and Dark Matter

False; they are not similar in that they both appear to be slowing the expansion of the universe.

Hubble's law

States that galaxies are receding from us at a speed that is proportional to their distance.

Classification of our Sun on H-R Diagram

Classified as a yellow dwarf.

Milky Way galaxy

True; our galaxy is called the Milky Way.

Galaxy absorption

True; our galaxy is currently absorbing other galaxies.

Formation of protostar

Nuclear fusion does not occur prior to the formation of the protostar.

Stars life span as giants

False; stars do not spend most of their life span as giants.

Stars life span as main-sequence stars

True; stars spend most of their life span as main-sequence stars.

Milky Way classification

False; the Milky Way is classified as a spiral galaxy.

Class of the Sun

The Sun belongs to the main-sequence star class.

Sun classification

True; the Sun is considered an average star.

Protosun

Means 'the Sun in the making.'

Formation of solar system

True; the bodies of our solar system began forming about 5 billion years ago.

Star's color index

A quick way of determining its temperature.

Type O and B stars

They are hotter and younger compared to type K and M stars.

Stars with masses comparable to our Sun's

Are white dwarfs.

Main sequence stars fusion

True; main sequence stars are fusing hydrogen into helium in their cores.

Star's total life on main sequence

True; about 90% of the star's total life is spent on the main sequence.

Recurrent nova

A recurrent nova could eventually build up to a Type I supernova.

Horizontal branch star

A star is on the horizontal branch of the H-R diagram if it is burning both hydrogen and helium.

Galactic Year

The Galactic Year is the time for our solar system to orbit the Galaxy; it is about 225 million years.

Galactic Center distance

Our Sun lies about 30,000 light-years out from the Galactic Center.

Milky Way galaxy type

Detailed measurements suggest our Milky Way is a barred spiral galaxy.

Densest stars

The densest stars known to exist are neutron stars.

Expanding universe theory

The discovery that the universe appears to be expanding led to a widely accepted theory called the Big Bang.

First elements after Big Bang

The first elements to form after 'Big Bang' were helium and hydrogen.

Hottest main-sequence stars

The hottest main-sequence stars are also the most massive.

Star brightness measure

The measure of a star's brightness is called its magnitude.

Most dense objects

The most dense objects known are black holes.

Dominant factor in star life

The dominant factor in the life of a star is gravity.

Main factor after nuclear fuel

The main factor that determines what will happen to a star after it consumes all of its nuclear fuel is mass.

Hubble's major contribution

Hubble's major contribution to Cosmology was identifying numerous new galaxies outside the Milky Way.

Coolest surface temperature stars

Red stars have the coolest surface temperature.

Highest surface temperature stars

Blue stars have the highest surface temperature.

Least massive main-sequence stars

Red main-sequence stars are the least massive.

Most massive main-sequence stars

Blue main-sequence stars are the most massive.

Big Bang Theory events

About 13.7 billion years ago, our universe started with a huge explosion.

Largest size objects

Galactic clusters have the largest size.

Stars within 16 light years

Most stars within 16 light years are Main sequence red dwarf and yellow stars.

Brightest stars type

Of the 100 brightest stars, red dwarfs are the most common.

TOI 700d star type

TOI 700d is an exoplanet within its star's habitable zone; its star is a Red Dwarf.