Solar System Astronomy Chapter 1

requirements of being a planet?

(1) orbits a star (2) is large enough for its own gravity to make it round (3) has cleared most other objects from its orbital

How fast do we spin around earth's axis?

1000 km/hr

how fast does our solar system orbit the center of the milky way galaxy?

800,000 km/ hr

What speed does light travel?

@ the speed of light which is 300,000 kilmoeters per second, meaning a light second is about 300,000 kilometers

The Local Group

A group of 40 galaxies--the milky way is one of th elargest

ecliptic plane

Earth's orbital path defines a flat plane that we call the ecliptic plane. Earth's axis is tilted by 23.5 from a line perpendicular to the ecliptic plane. This axis tilt happens to be oriented so that the axis points almost directly at a star called Polaris, or the North Star.

Big BanG

Galaxies must have been closer together in the past, and if we go back far enough we must reach the point at which expansion began aka the big bang

What is happening to our universe?

IT'S EXPANDING! space is growing between galaxies.

galactic rotation

Our solar system, located about 27,000 light years from the galactic centers, completes one orbit of the galaxy in about 230 milllion years.

chemical progression of the universe

The early universe contained only the simplest chemical elements: hydrogen and helium (and a trace of lithium.) Evidence shows that other elements (carbon, nitrogen, oxygen, iron) were manufactured by stars--through nuclear fusion and other nuclear reactions.

solar system

The sun and all the material that orbits it. Including planets, dwarf planets, and solar system bodies. Although the term solar system technically refers only to our own solar system, it is often applied to other star systems as well.

galactic movement

Virtually every galaxy outside the Local Group is moving away from us (found by Hubble Space telescope) and the more distant the galaxy, the faster it appears to be moving

cluster (or group) of galaxies

a collection of galaxies bound together by gravity--small collections (up to a few dozen galaxies) are generally called groups, while larger collections are called clusters.

superclusters

a gigantic region of space in which many groups and clusters of galaxies are packed more closely together than elsewhere in the universe

galaxy

a great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common center

comet

a relatively small and ice rich object that orbits a star

asteroid

a relatively small and rocky object that orbits a star

star system

a star (sometimes more than one star) and any planets and other materials that orbit it

small solar system body

an asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet

dwarf planet

an object that meets the first two criteria of being a planet but has not cleared its orbital past (ex. pluto)

moon

an object that orbits a planet.

AU

astronomical unit--the average distance between Eartha and the Sun, which is about 150 million kilometers. More technically, 1 AU is the length of the semimajor axis of Earth's obit.

copernican revolution

earth is not the center of the universe but rather just one planet orbiting the sun

earth's rotation

earth rotates from west to east--counterclockwise as viewed from the North Pole

star

large, glowing ball of gas that generates heat and light through nuclear fusion in its core. Our sun is a star.

planet

moderately large object that orbits a star and shines primarily by reflecting light from its star.

How fast does our planet orbit the sun?

more than 100,000 km/hr

Milky Way Galaxy

our solar system belongs to the huge, disk-shaped collection of stars. The milky way is a relatively large galaxy, containing more than 100 billion stars. Our solar system is located a little over halfway from the galactic center to the edge of the galactic disk, one of the largest in the local group. The Milky Way is only one of roughly 100 billion galaxies in the observable universe.

Voyage scale model

shows the sun and the planets, and the distances between them, at one ten-billionth of their actual sizes and distances. The model Sun is about the size of a large grapefruit, Jupiter is about the size of the ball point in a pen. On this scale, the palm of your hand can cover the entire region of the universe in which humans have so far traveled.

stellar lives

stars go through life cycles--a star is born when gravity compresses the material in a cloud to the point at which the center becomes dense enough and hot enough to generate energy by nuclear fusion. The stars "lives" as long as it can shine with the energy from fusion, and dies when it exhausts its usable fuel.

light year

the distance that light can travel in 1 year, which is about 9.46 trillion kilometers. The light year is a unit of distance, not of time.

relationship between time and distance in space

the farther away we look in distance, the further back we look in time

expansion (of the universe)

the increase in the average distance between galaxies as time progresses

galactic recycling

the most massive stars die in titanic explosions called supernovae. The returned matter mixes with other matter floated between the stars in the galaxy, eventually becoming part of new clouds of gas and dust from which new generations of stars can be born.

orbit (revolution)

the orbital motion of one object around another due to gravity. For example, earth orbits the sun once a year.

observable universe

the portion of the entire universe that can be seen from earth, at least in principle. The observable universe is probably only a tiny portion of the entire universe. The distance of 14 billion light years marks the boundary (or horizon) of our observable universe.

nuclear fusion

the process by which light weight atomic nuclei smash together and stick (or fuse) to make heavier nuclei

rotation

the spinning of an object around its axis. Earth rotates once each day around its axis, which is an imaginary line connecting the North and South poles.

universe (or cosmos)

the sum of all matter and energy--that is, all galaxies and everything between them

how fast does our solar system move among the stars of the local solar neighborhood?

typical speeds of 70,000 km/hr

satelitte

used more generally to refer to any object orbiting another object

dopplar shifts

we measure the speeds of galaxies by spreading their light into spectra and observing what we call dopplar shifts