Space Physics: Stars, Galaxies, Solar System

Space Physics

• Space physics is the study of planets, moons, stars, galaxies and the universe

Learning Objectives: Stars, Galaxies and the Universe

• Galaxies consist of many billions of stars.
• The Sun is a medium-sized star within the Milky Way galaxy composed mainly of hydrogen and helium.
• The Sun emits energy in the infrared, visible, and UV regions of the electromagnetic spectrum.
• Stars in the Milky Way are much farther from Earth than the Sun.
• The Milky Way is among billions of galaxies in the Universe, with a diameter of roughly 100,000 light-years.
• Astronomical distances are measured in light-years, where one light-year is the distance light travels in a vacuum in one year.
• One light-year is equivalent to 9.5 x 10^15 meters.

Learning Objectives: Solar System

• The Solar System includes one start, the Sun.
• The Solar System includes eight named planets in order from the Sun.
• The Solar System includes minor planets, including dwarf planets like Pluto, and asteroids in the asteroid belt.
• The Solar System includes moons which orbit the planets, comets and natural satellites.
• The Solar System includes smaller solar system bodies, including comets and natural satellites.
• The four planets nearest the Sun are rocky and small.
• The four planets farthest from the Sun are gaseous and large
• Planetary data such as orbital distance, orbital duration, and surface temperature can be analyzed and interpreted.
• You can calculate the time it takes light to travel a significant distance within the Solar System.

Learning Objectives: Earth

• Earth is a planet that rotates on a tilted axis, completing one rotation in approximately 24 hours, explaining the apparent daily motion of the Sun and the day/night cycle.
• Earth orbits the Sun once in roughly 365 days.
• It takes approximately one month for the Moon to orbit the Earth, explaining the periodic nature of the Moon's cycle of phases.

Ranking of Entities (Smallest to Largest)

• The order from smallest to largest is: Planet, Dwarf Planet, Star, Solar System, Galaxy, and Universe.

Definitions

• Universe encompasses all space, matter, and energy, including time.
• Galaxy refers to a collection of stars and their solar systems grouped together.
• Milky Way is the galaxy containing the Sun and Solar System.
• Star is a celestial body made of gas that emits its own light.
• Solar system includes the Sun, planets, and other orbiting bodies.
• Planet is a large body made of rock or gas that does not emit light but orbits a star within a solar system.
• Exoplanet orbits a star other than the Sun.
• Dwarf planet refers to a lump of rock smaller than a planet, orbiting the Sun, nearly spherical, with other objects around it.
• Moon is a rocky body orbiting a planet, also known as a natural satellite.
• Comet consists of dust particles frozen in ice, orbiting the Sun.
• Asteroid is a lump of rock that may be part of a planet, moon, or left over from solar system formation, and orbits the Sun.
• Asteroid belt consists of a large number of asteroids between Mars and Jupiter.
• Meteor is a piece of rock or dust that creates a streak of light as it enters the Earth's atmosphere and burns up.
• Meteorite is a stony or metallic object fallen to Earth from outer space without burning up.
• Constellation is a collection of stars forming a pattern in the sky.
• Orbit is the regular, repeating (elliptical) path an object takes around another in space.

The Universe

• The Universe includes everything: all space, matter, energy, and even time.
• Much of the observable matter in the Universe is made up of hydrogen atoms.
• The Universe contains at least 100 billion galaxies.
• The Universe is about 13.8 billion years old, based on the ages of the oldest stars and the expansion rate of the universe.

Origin of the Universe

• The Big Bang Theory describes the origin of the Universe.
• About 13.8 billion years ago, all the matter in the Universe emerged from a tiny, single point due to a violent explosion.
• The explosion caused the Universe to expand rapidly.
• Within a tiny fraction of a second, gravity and all other forces formed, and matter (atoms) appeared.

Galaxies

• A Galaxy is a huge collection of gas, dust, billions of stars, and their solar systems, all held together by gravity.
• Earth is located in the Milky Way galaxy.

The Milky Way

• The Milky Way is a barred spiral galaxy.
• It appears as a milky band of light in the night sky.
• It contains at least 100 billion stars, including the Sun.
• The Milky Way has a diameter of 100,000 light-years, due to its stars forming a large disk.
• The Solar System is roughly 25,000 light-years away from the center of the Milky Way.
• The Sun revolves around the center of the Milky Way, taking about 250 million years to complete one revolution.

Light Year

• One light year is equal to 9,500,000,000,000,000 meters, or 9.5 trillion km.

Scientific Notation

• Scientific notation is used to express very large (or very small) numbers concisely.
• Written as the product of a number between 1 and 10 with a power of 10.
• Example is 1,000 = 1 x 10^3
• One light year = 9,500,000,000,000,000 m = 9.5 x 10^15 m!

Solar System

• A solar system is a star (e.g., the Sun) and the planets and other bodies that orbit around it.

Stars

• A star is a body in space made of gas that gives out its own light.

The Sun

• The Sun is the largest object in the Solar System, containing 99.8% of the system's mass, located at the center.
• The Sun is composed of 91% hydrogen and 9% helium atoms.
• The Sun radiates most of its energy in the infrared, visible, and UV regions of the electromagnetic spectrum.
• The Sun's gravity holds the Solar System together.

Stars Other Than the Sun

• The closest star to Earth other than the Sun is Proxima Centauri.
• Proxima Centauri is 4.37 light years away from Earth.

Planets

• A planet is a large body made of rock or gas that does not emit light but orbits a star in a solar system.
• The order of the planets in the Solar System are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Dwarf Planets

• A dwarf planet is a lump of rock smaller than a planet, that has nearly spherical, orbits the Sun, but has other objects around it.
• Examples of dwarf planets include Eris, Makemake, Ceres, Pluto and Haumea.

Moons

• A moon is a rocky body orbiting a planet, also known as a natural satellite.

Orbits

• An orbit is a regular, repeating path that one object takes around another in space.
• Planetary orbits are elliptical.
• All planets orbit on the same orbital plane.

Asteroids, Comets and Meteors

• Asteroid is a lump of rock that is a part of a planet or a moon, or left over from when the Solar System was formed, that is in orbit around the Sun.
• Comet is a body in space made of dust particles frozen in ice, which orbit the Sun
• Meteor is a meteoroid that makes a streak of light in the night sky as it enters the Earth's atmosphere and burns up
• Meteoroid is a piece of rock, metallic fragment or dust coming from an asteroid, comet or planet that orbits the Sun
• Meteorite is a meteoroid that has fallen to Earth from outer space without burning up

The Asteroid Belt

• Asteroids are numerous between Mars and Jupiter and are remnants from the early formation of the Solar System.
• Orbits of asteroids can be changed by Jupiter's massive gravity.
• Mars can also knock asteroids out of the belt.

Visibility of Objects in the Sky

• We see planets and other objects in the sky because light is reflected off them into our eyes.
• Five planets can be seen with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn.
• Objects such as stars, planets, the Moon, comets, meteors, and manmade satellites can be seen without a telescope.

Day and Night

• Earth rotates on its axis every 23 hours and 56 minutes.
• The Earth's axis is tilted 23.5 degrees.
• Day occurs on the side of Earth that faces the Sun.
• Night occurs on the side of Earth that is away from the Sun.

Moon Phases

• Like Earth, the Sun shines on one half of the Moon and not the other.
• The amount of the illuminated half that we can see changes as the Moon travels through its orbit
• The phases of the Moon are New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent.
• The lunar cycle is 29.53 days.

Lunar Eclipse

• A lunar eclipse occurs around the time of a full moon.
• The Sun, Earth, and Moon are lined up, causing the Moon to be in the Earth's shadow.
• A lunar eclipse has umbra and penumbra

Frequency of Lunar Eclipses

• The Moon goes around Earth monthly, but it does not always enter Earth's shadow.
• The Moon's path around Earth is tilted compared to Earth's orbit around the Sun, thus the Moon can be behind Earth but still shone by sunlight.