ASTR 1210 - Chapter 1: A Modern View of the Universe

Where is our solar system located in relation to our galaxy?

~Halfway from the galactic center to the edge of the galactic disk

How does the size of the Milky Way Galaxy compare to other galaxies in the local group?

One of the two largest galaxies

How are galaxies and galaxy clusters arranged on a large scale?

in giant chains and sheets with huge voids between them

What is the supercluster of our local group?

Laniakea, Hawai’ian for “immense heaven”

What are the astronomical distance measurements?

Astronomical units (AU) and Light years (LY)

How long does it take light to reach Earth from the moon? The sun?

1 second, 8 minutes

What is the significance of astronomical distance on time?

Because it takes light a set amount of time to reach Earth, astronomical objects that are positioned x light years away are viewed in a delay. Ex) We see Sirius as it was 8 years ago, because it is 8 light years away from us; We see Orion Nebula as it was 1350 years ago, because it is 1350 light years away from us.

“The farther away we look in distance, the further back we look in time”

What are the current criteria for an object to be considered a planet?

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

What is the difference between a planet and a dwarf planet?

An object that meets the first two criteria but has not cleared its orbital path, like Pluto, is designated a dwarf planet.

What is the measured age of the universe?

14B Years

How does the measured age of the universe create limitations for viewing space?

14B light years is the maximum distance that the observable universe can theoretically be viewed

What is the nearest star system to our own?

Alpha Centauri, 4.4 light years away

JWST

James Webb Space Telescope

Cosmic Address

Key levels of structure in our universe. Universe → Local Supercluster → Local Group → Milky Way Galaxy → Solar System → Earth

Solar System (aka Star System)

A star and all of the objects that orbit it (asteroids, comets.. etc)

Milky Way Galaxy

Galaxy

A great island of stars in space, all held together by gravity and orbiting a common center

Local Group

Galaxy Clusters

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.

Astronomical Unit

Earth’s average distance from the sun (150M Km

Light Year

Distance light travels in 1 year (10T Km

Speed of Light

300,000 km per second

Light Second

300,000 km

star

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

planet

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

exoplanet

(or extrasolar planet) A planet orbiting a star other than our Sun.

moon (or satellite)

An object that orbits a planet. The term satellite is also used more generally to refer to any object orbiting another object.

Asteroid

A relatively small and rocky object that orbits a star.

comet

A relatively small and ice-rich object that orbits a star.

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.

World

In the context of astronomy, any planet, dwarf planet, moon, or small body that we could imagine visiting.

universe (or cosmos)

The sum total of all matter and energy—that is, all galaxies and everything between them.

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.

Rotation

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

orbit (or revolution)

The orbital motion of one object around another due to gravity. For example, Earth orbits the Sun once each year.

expansion (of the universe)

The increase in the average distance between galaxies as time progresses.

Voyage Scale Model Solar System

Shows size and distances of the solar system at one ten-billionth of its actual size

Order of magnitude estimate

Estimates good to about the nearest power of 10

Describe the events of the universe from the big bang, expansion, and the age of the universe?

Describe expansion of the universe?

While the universe as a whole expands, individual galaxies and clusters do not expand

How is a star born?

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

What separates life and death of a star?

A star lives as long as it can shine with energy from fusion and dies when it exhausts its usable fuel

What happens to stars after they die?

Returned matter mixes with other matter floating in space, eventually becoming part of new clouds of gas and dust

What are the chemical elements of the early universe?

Hydrogen, Helium, Lithium

What elements are we primarily made of?

Carbon, Nitrogen, Oxygen, Iron

Where did other elements of the universe come from?

Manufactured by stars through nuclear fusion and nuclear reactions accompanying explosions that end stellar lives and merging of dead stars

Created inside stars that lived and died before our planet/sun

Big Bang

The point at which expansion of the universe begins

Nuclear fusion

The process in which lightweight atomic nuclei smash together and stick to make heavier nuclei

Supernovae

Titanic explosion that accompanies the death of a massive star

How often does the Earth rotate?

Once a day

In what direction does the earth rotate?

West to East (Counterclockwise as viewed from the north pole)

Describe the relationship between rotation speed and location on Earth?

Closer to the equator the faster the speed of rotation

How often does the Earth orbit the sun?

Once a year

What is the speed of Earth’s orbit around the sun?

100K Km per hour

In what direction is Earth’s axis pointed?

towards Polaris

What is the average earth-sun distance?

1 AU

What is the tilt of Earth’s axis?

23 ½ Degrees from a line perpendicular to the ecliptic plane

In what direction does the Earth orbit the Sun?

Counterclockwise as viewed from above the North Pole

Why does Earth orbit the Sun and rotate in the direction that it does?

Strong evidence indicates that the Earth and the other planets were born in a spinning disk of gas that surrounded our Sun as it formed and earth rotates and orbits in the same direction that the disk was spinning

What are the two major components of the motion of the solar system in the Milky Way?

1) Stars in the local solar neighborhood move randomly relative to one another at about 70k Km/Hr; 2) the galaxy’s rotation carries us at about 800k Km/Hr

What is revealed by studying the galaxy’s rotation?

Mass distribution of the galaxy based on the different speeds of stars at different distances from the galactic center

Where does most of the mass of a galaxy lie?

In the surrounding halo that encompasses the disk, made of dark matter

What are Edwin Hubble’s two facts of the outside of the Local Group?

1) Virtually every galaxy outside the local group is moving away from us; 2) The more distant the galaxy, the faster it appears to be racing away → Why? The entire universe is expanding

Describe the raisin cake analogy?

The fact that the cake is expanding during baking means that all the raisins are moving away from the Local Raisin, with more distant raisins moving away faster

How does the speed of expansion relate to the age of the universe?

The faster the rate of expansion, the more quickly the galaxies reached their current positions, and therefore the younger the universe must be.

How are the distances between galaxies measured?

The speeds of the galaxies are measured by spreading their light into spectra and observing Doppler Shifts

Summarize the motions of the universe

We spin around Earth’s axis at 1000km/hr, Earth orbits the Sun at 100,000km/hr, the Solar System moves among the stars of the local solar neighborhood at 70,000km/hr and orbits the center of the Milky Way at 800,000km/hr

Axis

Imaginary line connecting the North Pole to the South Pole

Ecliptic Plane

The plane of Earth’s orbit around the Sun

Axis Tilt

The amount by which a planet’s axis is tilted with respect to a line perpendicular to the ecliptic plane.

Dark Matter

Matter that we infer to exist from its gravitational effects but from which we have not detected any light; dark matter apparently dominates the total mass of the universe

Dark energy

Name sometimes given to energy that could be causing the expansion of the universe to accelerate