Download Tour of the Universe

Solar System A collection of planets, moons, asteroids, comets, and other rocky objects travelling in elliptical orbits around the Sun under the influence of its gravity. The Sun and the planets ● Star; from a giant cloud of molecular hydrogen gas that gravitated together forming clumps of matter that collapsed and heated up. ● A gas disc around the young, spinning Sun evolved into the planets. Planets were formed about 4.6x10^9 years ago. The high temperature close to the Sun provide the compounds with high condensation temperature to remain solid, that hold the particles that make up these planets together: Mercury, Venus, Earth and Mars. ● The planets that are farther away from the Sun are formed from cores of rock and metals and an abundance of ice. These planets include Jupiter, Saturn, Uranus and Neptune. These planets are called “Gas Giants” or “jovian”. ● Pluto is a dwarf planet. ● The planets move in an elliptical orbit. ● Beyond Neptune is the Kuiper belt which is a large asteroid belt. Source of short period comets and contains dwarf planets. ● The Kuiper belt is set to be the next frontier of exploration in our solar system. ● 6 of the planets have moons orbiting them. Them bigger ones have more moons than the smaller ones. ● Earth's moon was formed 4.5 billion years ago from material ejected when a collision occurred between a Mars­size object and the Earth. Asteroids ● Rocky objects orbiting the Sun­ with millions of them contained in solar orbit in the asteroid belt situated between Mars and Jupiter. ● Those smaller than 300km are irregularly shaped because their gravity is not strong enough to make them into spheres. ● Some are so big that they could be considered minor planets. Ex: Ceres. Comets ● Irregular objects a few km big made up of frozen gas, rock, and dust.Takes thousands of years to orbit the sun. ● When close to the sun, the gases evaporate and create a tail that always points away from the sun. Stars (Types and Groups) ● Stars are formed when the gravity causes the gas to condense in a nebula. The atoms lose the potential energy that they had and it turns into kinetic energy. Group of stars Binary ● It is thought that around 50% of the stars nearest to the Sun are part of a star system comprising two or more stars. ● Binary stars consist of two stars that rotate about a common centre of mass. ● Careful measurement of the motion of the stars in a binary system allows their masses to be estimated. Stellar Cluster ● A group of stars that are positioned closely enough to be held together by gravity. ● They range from a few dozen stars to a million stars. ● All the stars were formed at the same time in the same nebula. ● OPEN CLUSTERS consist of up to several hundred stars that are younger than 10 billion years old and may still contain some gas and dust. ● They are located within our galaxy, the Milky Way, and also lay within a single plane. ● GLOBULAR CLUSTERS contain many more stars and are older than 11 billion years old, so they contain little gas and dust. ● Globular Clusters are essentially spherically shaped. Constellations ● Patterns formed by the stars that are in the same general direction when viewed from Earth ● Some ancient societies used them for religious reasons. ● Today they are used for telescopic study. ● Some of the stars are much closer to Earth than others. Because of proper motion, they will look different in ten thousand years. ● These stars are not held together by gravity. ● Proper motion­ ​
the part of the apparent motion of a fixed star that is due to its actual movement in space relative to the sun. Nebulae Nebulae​
are regions of intergalactic clouds of dust and gas. Since all stars are “born” out of nebulae, these regions are known as ​
stellar nurseries​
. Origins Nebulae have two different origins: ● The first origin occurred in the “matter era” around 380,000 years after the Big Bang. Dust and gas clouds were formed when nuclei captured electrons electrostatically and produced the hydrogen atoms that gravitated together. ● The second origin of nebulae is from the matter that ejected from a supernova explosion. ● Other nebulae can form in the final, ​
red giant​
(a dying star that engulfs surrounding planets), stage of a low mass star like the Sun. Types of Nebulae ● Emission Nebulae​
­ Clouds of high temperature gas. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation as they fall back into lower energy states. Emission nebulae are usually the sites of recent and ongoing star formation. ● Reflection Nebulae​
­ Cloud of dust which are reflecting the light of a nearby star or stars. Reflection nebulae are also usually sites of star formation. Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae. ● Dark Nebulae​
­ Clouds of dust which are blocking light from whatever is behind them. Very physically similar to reflection nebulae but look differently because of the geometry of the light source, and the cloud. Often seen in conjunction with reflection and emission nebulae. ● Planetary Nebulae​
­ Shells of gas thrown out by some stars near the end of their lives. Although they share a similar name, they have nothing to do with planets. The name was invented because they often look like little planets in small telescopes. Galaxies Galaxies​
are creations of stars, gas, and dust held together by gravity and contain billions of stars. Well Known Galaxies The Milky Way and Andromeda are a few examples of well known galaxies. The Milky Way contains about 3 x 10^11 stars and, probably, at least as many planets. Clusters Some galaxies are isolated, but most are in groups known as ​
clusters​
that have anything from a few dozen to a few thousand galaxies within them. The Milky Way is a part of a cluster of about 30 galaxies called the “​
Local Group​
” which includes Andromeda and Triangulum. Types of Clusters ● Regular clusters ​
consist of a concentrated core and are spherical in shape. ● Irregular clusters ​
also exist, with no apparent shape and a lower concentration of galaxies. ● Superclusters​
are even larger structures that form a network of sheets and filaments. About 90% of all galaxies are found within superclusters. Types of Galaxies The Milky Way and Andromeda are members of ​
spiral galaxies​
, which are the most common type of galaxies. Spiral galaxies have a disc­shape with spiral arms that are spread out from a central galactic bulge that is the most dense collection of stars within a galaxy. The spiral arms contain many young blue stars and a large amount of dust and gas. It is speculated that at the center of a galactic bulge, there is a black hole. Other galaxies are elliptical in shape and are ovoid and spherical. These galaxies contain much less gas and dust than spiral galaxies and are thought to have been formed from collisions between spiral galaxies. Irregular galaxies are shapeless and appear to have been stretched by the presence of other larger galaxies. Universe Astrophysics D.3 The Big Bang Theory ­about 13.7 billion years ago, the universe was smaller than the size of an atom ­at that instance, the entire universe exploded (Big Bang) ­during this expansion, time and space came into existence ­the initial temperature was 1032 K ­after one second, the temperature dropped to 1010 K ­the universe has continued to cool to 2.7 K ­the universe has continued to expand The Expansion of the Universe ­as galaxies move apart, the space between them becomes stretched ­the space through which the electromagnetic radiation travels is expanding and it stretches out the wavelength of the light ­the further away the source of the light, the more space becomes stretched Age of the Universe ­the age of the universe can be estimated using Hubble’s law ­Hubble’s law: v = H od Where v= velocity of recession (km/s) d= distance of the galaxy from Earth H o = the constant of proportionality between the recessional velocity of galaxies and their distance from Earth (about 70 km s−1 M pc−1 ) ­Reminder: pc is parsec, the most commonly used unit of distance in astrophysics ­Assuming that Hubble’s law has held true for all galaxies at all times, the light from the most distant star has taken the age of the universe to travel to us. ­If the light was emitted immediately after the Big Bang, then the space between the galaxy and the Earth must have expanded at slightly less than the speed of light for the light to have just reached us. ­this makes the recessional speed of the galaxy almost that of the speed of light, c. ­the distance that light has travelled from the galaxy = c x T, where T is the age of the universe. Derivation of the age of the Universe Current Topics Recently, the Hubble Telescope captured this image of the “Bubble Nebula” named so because of its spherical shape and blue color. A “Dark Dwarf Galaxy” was recently discovered that is almost entirely made up of dark matter. The most distant galaxy that we are currently aware of is z8 GND 5296. This galaxy is 3.4 billion light years away. http://phys.org/news/2015­01­universe.html Last Sunday, on April 17, Jupiter could be seen to the left of the moon. http://www.space.com/32594­moon­and­jupiter­pair­off­sunday.html