Space Physics: Quick Reference

Earth rotates around itself once every 24 hours, creating day and night.
Earth orbits the Sun in approximately 365 days, causing seasons due to the tilt of its axis.
The Moon orbits the Earth in about one month, resulting in different phases of the Moon as it reflects sunlight.
Main phases of the Moon: New Moon, First Quarter, Full Moon, and Third Quarter.
Orbital speed is calculated as $v = \frac{2 \pi r}{T}$ , where $r$ is the radius and $T$ is the orbital period.

The solar system includes a star (Sun), eight planets, minor planets (Pluto, asteroids), moons, and comets.
Planets in order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Planets near the Sun are small and rocky; planets far from the Sun are large and gassy.

Nebula: Cloud of dust and gas.
Gravity pulls mass to the center, forming a protostar.
A stable star is formed when the inward force of gravity equals the outward force of heat.
The remaining mass spins in an accretion disk.
Gravity clumps dust and gas into protoplanets and planets.

Solar winds push lighter elements away, causing closer planets to be rocky and further planets to be gassy.
Gravity depends on mass; greater mass results in a stronger gravitational field.
Orbits can be circular or elliptical; comets have highly elliptical orbits.
As a comet moves away from the Sun, its speed decreases and potential energy increases, and vice versa.
Orbital distance affects gravitational pull and orbital time; density indicates the material composition of a planet.
Temperature ranges and the presence of an atmosphere also affect a planet's characteristics.

Stars are made of hydrogen and helium and emit infrared, visible light, and ultraviolet radiation.
Nuclear fusion of hydrogen to helium occurs within stars.
A star is stable when the inward force of gravity equals the outward force of heat.
Galaxies are made up of billions of stars; our galaxy is the Milky Way, which is 100,000 light-years in diameter.
A light-year is the distance light travels in one year.

Evidence for the expanding universe: distant stars' brightness decreases, redshift, and cosmic microwave background radiation (CMBR).
Redshift is the increase in wavelength of electromagnetic radiation from receding galaxies.
CMBR is radiation detectable everywhere in space, produced shortly after the universe was formed.
Hubble constant (H0) relates the speed and distance of galaxies: $H_0 = \frac{V}{D}$ , where V is velocity and D is distance.
The age of the universe can be estimated using the Hubble constant: $Age = \frac{1}{H_0}$