Astronomy Exam #3 Study Guide

Understand the different levels of organization of the cosmos: solar system, galaxy, universe

Our Solar System consists of the Sun, orbiting planets including Earth, along with numerous moons, asteroids, comet material, rocks, and dust. Our Sun is just one star among the hundreds of billions of stars in our Milky Way Galaxy. If we shrink the Sun down to smaller than a grain of sand we can imagine our Solar System to be small enough to fit onto the palm of your hand. Pluto would orbit about an inch from the middle of your palm. On that scale with our Solar system in your hand, the Milky Way Galaxy, with its 200-400 billion stars would span North America. Galaxies come in many sizes. The Milky Way is big but some galaxies like our neighbor Andromeda is much larger. The Universe is all of the galaxies-billions of them. Our telescopes allow us to study galaxies beyond our own in exquisite detail. Our Earth orbits the Sun in our Solar System. Our Sun is one star among the billions in the Milky Way Galaxy. Our Milky Way Galaxy is one among the billions of galaxies in our Universe.

Understand the concept of lookback time.

The amount of time since the light we see from a distant object was emitted. If an object has a lookback time of 400 million years we are seeing it as it looked 400 million years ago.

How old do we believe the universe to be? How about our Sun? The Earth?

1. 13.8 billion years old (14 billion years old) 2. 4.6 Billion years old 3. 4.54 billion years old

What is Olbers' Paradox? How do we resolve it?

1. A paradox pointing out that if the universe were infinite in both age and size with stars found throughout the universe, then the sky would not be dark at night. 2. To resolve Olbers' Paradox we use Hubble's Law that shows that the more distant a galaxy higher is its red-shift. So the visible light from galaxies that are too far away would be red-shifted to invisible wavelengths. So stars beyond a certain depth of space would go invisible resolving the Olber's Paradox.

What are standard candles?

An object for which we have some means of knowing its true luminosity, so that we can use its apparent brightness to determine its distance with the luminosity-distance formula.

What are the different parts of our galaxy? What are the differences between them?

1. Galactive Disk, Nucleus, Bulge, Spiral arms, Globular clusters, Halo 2. Parts of Galaxy + Galactic disk: Most of the Milky Way's more than 200 billion stars are located here. The disk itself is broken up into these parts: Nucleus, Bulge, and Spiral arms. + Nucleus: Center of the disk + Bulge: Area around the nucleus including the immediate areas above and below the plane of the disk. + Spiral arms: These extend outward from the center. Our solar system is located in one of the spiral arms of the Milky Way. + Globular clusters: A few 100ed of these are scattered above and below the disk. The stars here are much older than those in the galactic disk. They are spherically shaped clusters of up to a million or more stars. They are found primarily in the halos of galaxies and contain very old stars. + Halo: The spherical region surrounding the disk of a spiral galaxy. A large, dim, region that surrounds the entire galaxy... It's made of hot gas and possibly dark matter.

What is Hubble's Law? How does it lead to the idea of the Big Bang? How does the Hubble Constant connect to our estimated age of the universe?

1. It's a mathematical expression of the idea that more distant galaxies move away from us faster by using the formula v=Ho * d. V is a galaxy's speed away from us, d is the distance, and Ho is Hubble's constant. 2. Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang. It also states that the universe is expanding outward. 3. The inverse of Hubble's constant tells us how long it would have taken the universe to reach its present size if the expansion rate had never changed.

What is the cosmic background radiation? What does it tell us about the early universe?

1. It's electromagnetic radiation coming from every direction in the universe, considered the remnant of the Big Bang and corresponding to the black-body radiation of 3K. It's also known as Cosmic Microwave Background. 2. The Big Bang predicts that the radiation that began to stream across the universe at the end of the era of nuclei should still be present today. Sure enough, we find that the universe is filled with a cosmic microwave background. The Big Bang predicts that some of the original hydrogen in the universe should have fused into helium during the era of nucleosynthesis. Scientists concluded that if the Big Bang had really occurred this radiation should be permeating the entire universe and should be detectable with a microwave antenna.

What is our galaxy called? How big is it? How many stars does it have? What type is it?

1. Milky Way Galaxy 2. 100,000 light-years 3. 400 Billion stars 4. Barred Sprial galaxy

How do we calculate the masses of galaxies? How does this connect to dark matter?

1. Mr= r * v^2 /G or Mr= r* v^2 2. Since gravitational lensing is sensitive to all matter in a galaxy, including dark matter, it tells us about the total mass in a gravity. By subtracting the mass in stars and gas, it's possible to measure the properties of the dark matter in galaxies.

How do they differ in shape, types of stars, and interstellar material?

1. Spiral galaxies have a thin disk and a central bulge. The bulge merges smoothly into nearly invisible halo that can extend to a radius of more than 100,000 lys. The galaxy's halo is considerably more difficult to see than its bulge and disk because halo stars are generally dim and spread over a large volume of space. Disk stars orbit in the same plane and include stars of all ages and masses, while halo stars have randomly oriented orbits and are all old and low in mass. The Milky Way's bulge stars exhibit a mixture of disk and halo. Other Spiral galaxies share these characteristics but in spiral galaxies with large bulges the orbits of bulge stars have more in common with the orbits of halo stars than with those of disk stars. are easily identified by observing three components common to all spiral galaxies. A spiral galaxy has a disk, a bulge, and a halo. The center of the galaxy is like a nucleus containing a sphere shaped bulge that houses old stars and is devoid of dust and gas. The circular shape of the galaxy comprises the disk. The arms of the spiral galaxy originate in the disk and are where new stars will form in a galaxy. The sun in our galaxy is located in one arm and its stars are created in this portion of the galaxy, which contains the most gas in the galaxy where it has rich blue stars. The halo isa spherical shaped collection of old stars and clusters known as globular clusters that's found in the outer edge of the galaxy. When a spiral galaxy has no arms, it's termed lenticular. Lenticular galaxies occur with barred spirals and are classified as SB0. Spiral galaxies are the most common galaxy of the universe, comprising about 77% of all known galaxies 2. Elliptical galaxies differ from spiral galaxies primarily in that they have only a halo component and lack a significant disk component. Their axes look much like the bulge and halo of a spiral galaxy without a disk. Elliptical galaxies come in a wide range of sizes. Relatively rare giant elliptical galaxies are among the most massive galaxies in the universe, while small dwarf elliptical galaxies are much more common. They usually contain very little dust or cool gas. They have little or no ongoing star formation. They look red or yellow in color because they lack the hoty, young, blue stars found on the disks of spiral galaxies. However large elliptical galaxies sometimes contain substantial amounts of very hot gas that emits x-rays much like the gas in the hot bubbles created by supernovae and powerful stellar winds in the Milky Way. They are round and diskless like elliptical galaxies but they are particularly small and much less bright. Because of these distinct differences they are a special subtype known as dwarf spheroidal galaxies. can be recognized by their elongated spherical shape and their lack of nucleus or bulge at the center. Although there's no nucleus, the galaxy is still brighter in the center and becomes less bright toward the outer edges of the galaxy. Stars, gases and other materials are spread throughout the elliptical galaxy. An elliptical galaxy can be nearly round, long, or cigar shaped. A great deal of mass in an elliptical galaxy is due to the presence of a central black hole. They have very little activity and contain mostly old stars of low mass because there aren't the gasses and dust needed to form new stars. 3. Irregular galaxies are composed of gasses, dust, stars, nebulous formations, neutron stars, black holes, and other elements common to all galaxies. They are named so because they have no definite shape but like all galaxies, they are in constant motion, moving outward and away from the center of our universe. Irregular galaxies are divided into two classifications Im and IO. Im galaxies occur most often among irregular galaxies and may show a trace of the spiral galaxy arms. IO galaxies are random and can be chaotic in nature. Approximately 20% of our galaxies are classified as irregular. 4. Barred Spiral Galaxy shares the same features and functions as regular spiral galaxies but they also have a bar of bright stars that lie along the center of the bulge, and extend into the disk. The bright bulge has very little activity here and contains mostly older red stars. The bar and arms have lots of activity including star formation. While the classification for barred spirals is the same as for regular spiral galaxies, the bar must be considered as well. Short bars correlate to tiger galaxies and will be included in the designation SBa. SBb has longer bars and SBc is the longest. Most astronomers now agree that the Milky Way is a barred spiral galaxy.

What are the methods we use to determine distances to: 1. The nearest stars 2. Nearby galaxies 3. Farthest galaxies

1. The method to determine nearest stars is called trigonometric parallax or parallax. We do this by observing how their positions appear to change as Earth orbits the Sun. 2. The method to determine nearby galaxies by using Cepheids. 3. The method to determine the farthest galaxies by using Hubble's law

How far away are each of the following: 1. near-Earth orbit 2. The Moon 3. Other planets 4. Other stars 5. Other galaxies

1. near-Earth orbit 26,560 kilometers (16503.6mi) and 20,200 kilometers (12551.6mi) above the surface 2. 238,855 miles 3. the Sun 92,955,828 mi, Mars 225 million km or 140 million miles, Venus 162 million miles or 261 million km, Saturn 1.2 billion km or 890,704,128 miles, Jupiter 483.77 million miles, Neptune 4.4 billion km or 2.80 billion miles, Pluto 5.05 km or 3.1 billion mi. 4. Polaris 433.79 light years, Alpha Centauri 4.37 light years 5. Andromeda 2,537,497 light years

What are the different types of galaxies?

The three different types of galaxies are: Spiral galaxies, Elliptical galaxies, and Irregular galaxies. + Spiral galaxies such as our Milky Way look like flat white disks with yellowish bulges at their centers. The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms. + Elliptical galaxies are redder, more rounded, and often elongated like a football. They contain very little cool gas and dust, though they often contain very hot, ionized gas. + Irregular galaxies appear neither disklike nor rounded.