Solar System

The Solar System

  • The story of Turtle Island (which in the textbook says is earth, but our Indigenous advisor says it’s North America) and Sky World (the heavens) is an example of a creation story which explains the existence of earth

  • The solar system is the sun and the objects within its gravitational influence, such as planets, moons, comets, and asteroids

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Nebular Theory

  • A nebula is a cloud of dust and gases in space

  • Astronomers have observed these to be areas where stars are forming, and so they are called “stellar nurseries”

  • The sun formed and it probably wasn’t the only star that formed in our solar system

  • The Sun’s solar wind pushed on the Nebula’s gases and dust

  • The dust and gas left became a thin disk (due to gravity) from which small bodies began to form, later becoming planets, moons, asteroids, and comets

  • 4.6 billion years ago, the sun formed in a nebula, it is the heart of our solar system

  • A star is defined as a body of plasma that is undergoing nuclear reactions and radiates energy

  • Our sun is of medium size compared to other stars and is 73% hydrogen (mass), 25% helium (mass), and the other heavier elements including carbon, oxygen, and iron

  • The sun will shine for another 5 billion years

  • We learned how the sun works when we figured out atomic energy

  • Via nuclear fusion, four hydrogen nuclei are converted into one helium nucleus and lots of energy

  • Stars radiate energy in many forms, including visible and UV light

The Planets

  • After the sun, the next largest astronomical bodies are planets

  • A planet is an astronomical object that orbits one or more stars and is capable of forming into a spherical shape under its own gravity

  • Planets do not create or radiate its own energy like a star does, they only reflect light from stars

  • There are 2 kinds of planets: rocky planets and gas giants

  • The planets in closest to farthest order from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Measuring Distances in Our Solar System

  • It is not practical to measure the distance to your house in cm, or to measure the solar system in km

  • Instead we use the average distance from earth to the sun, 150 million km, and call it one astronomical unit (1 AU)

    • Mercury is 0.39 AU from the sun (less than 1 AU because it is closer to the sun than earth)

    • Mars is 1.52 AU from the sun (more than 1 AU because it is farther from the sun than earth)

Measuring Bigger Distances

  • Outside our solar system, the distances to other celestial objects is so far that AU aren’t practical or useful

  • The distance light travels in a year is called a light-year (Ly) and is 63000 AU or 9 trillion km

  • Light can go around earth 7 times in 1 second, from the sun to earth is 8 minutes, and from the sun to Neptune is about 5 hours

Asteroid Belt

  • Asteroids are metallic, rocky bodies from pebble-sized to 1000 km in diameter and they don’t have an atmosphere (although most are less than 1 km)

  • They orbit the sun in the asteroid belt at a distance of about 3 AU

  • Albedo is how reflective something is

    • High albedo stars are easier to find

  • Analysis of asteroids is one way we’ve determined the age of the solar system

  • Earth and asteroids formed at about the same time, but the asteroids haven’t changed as much as earth has, so they are like fossils showing us what the early solar system had for materials

Dwarf Planets

  • Dwarf planets are roughly spherical and they may have an unusual orbit, possibly orbiting in a zone with many other objects

    • They are believed to have been created when the solar system formed

  • Dwarf planets that are still forming are called protoplanets

  • By watching this process, we can learn how planets form

Comets

  • Comets are made of ice and dust and are so often described as “dirty snowballs”

  • The most distant region of the solar system is the Oort Cloud, about 50,000 AU from the sun

    • This is about 20% of the distance to the sun’s nearest neighbor

  • The Oort Cloud is billions of fragments of ice and dust which orbit the sun and is a major source of comets

  • When interactions cause comets to leave the Oort Cloud, they may end up in an elliptical orbit which brings them near the sun. The sun heats the comet, causing the ice to break away and forming a tail that is millions of km long. The long tail reflects sunlight, making it easier to see from earth.

  • If a comet is visible from earth, it will slowly pass across the sky over several days

  • Its brightness depends on how close to the sun it gets, how close it is to the earth, its albedo, and how much material comes off creating a tail

  • Astronomers have been recording the appearance of comets since 2000 BCE

  • We regularly find new comets

    • In March 2020, a new comet was discovered and named Neowise and was visible to the naked eye in July 2020

Big Collisions

  • Asteroids and comets can have trajectories through the solar system which can cross paths with other objects (including earth)

  • Astronomers created the Torino Scale to communicate the possibility of such a collision, 0 meaning little to no risk of impact and 10 being an impact that could cause global climactic change

Small Collisions

  • Meteoroids are small rock/metal drifting through the solar system with no fixed path. Once it enters earth’s atmosphere it becomes a meteor despite nothing else about it having changed

  • Meteors are small rocks that enters earths atmosphere and streak brightly through the sky for a few seconds. We usually see them at altitudes between 80 and 120 km. They are often called shooting stars, although they aren’t stars. They are bright because the heat causes the surface of the meteor to vaporize

  • Meteorites are when meteors reach earth’s surface

Meteor Showers

  • Meteors are constantly happening at a rate of about 2-7 per night, but they are often hard to spot

    • meteor showers are when there is many meteors per hour or even several per minute

  • The Perseid meteor shower is one of the best known and is every year from mid-July to 2nd week of August

  • Meteor showers are due to comets. As the comet travels, the debris they leave behind are in predictable locations, and sometimes earth’s path goes through this locations.

  • All meteor showers are due to comets, although sometimes we haven’t yet identified the comet responsible, but we know to look for one

Meteor Storms

  • Meteor storms are particularly intense meteor showers, they produce at least 1000 meteors/hour

Meteorites

  • Scientists can classify meteorites based on what they are made of

  • From these efforts we found out that some came from the earth’s moon, Mars, and 1/16 of meteorites come from 4-Vesta (the second largest asteroid)

  • Vesta is currently one of only 7 identified solar system bodies we have physical samples of

    • Others are from earth, meteorites from Mars, meteorites from the moon, and samples returned from the moon, the Comet Wild 2, and the asteroids 25143 Itokawa and 162173 Ryugu

Observing the Night Sky

  • Without a telescope you can see Mercury, Venus, Mars, Jupiter, Saturn, the occasional comet, meteors, stars, constellations, satellites, the moon, the Andromeda Galaxy (supposedly), and the sun

  • The pupils of your eyes dilate to allow you to see better in various conditions, it is best to have your eyes adjusted to the darkness to do astronomy at night

  • If you want to look at a screen or a flashlight without ruining your night vision, use red lights