The Structure of the Universe All held together by gravitational forces

Measuring Distance in Space 1 light year = 9.5 x km or 9.5 trillion Light speed is 3.0 x 10 8 m/s and light year is the distance traveled by light in 1 year Astronomers use light years to measure distance since other units are so large. For example the nearest galaxy is the Andromeda galaxy, which is located at a distance of 21 quintillion km (21,000,000,000,000,000,000 km) away. Such a large figure is difficult to comprehend, when expressed in lightyears, the distance is 2.2 million lightyears, which is much easier to read. If you could travel at speed of light you could make 7.5 full rotations around the earth in 1 second

A lightyear in perspective…. How far away are other stars and galaxies when they are light years away? Pluto at the farthest reaches of our solar system is only light years away. Light from the sun would take 5.5 hours to reach Pluto, although most of it would be pretty diffused at that point. Our closest star cluster, Alpha Centauri, is 4.3 light years away. This means that the light emitted from these 3 stars would take 4.3 years to reach us.

We are seeing the past?? I can take the distance to the Andromeda Galaxy and divide by the speed of light Time = distance / speed That means it takes 2,218,226 years for the light from Andromeda galaxy stars to reach my eyes….so the stars I see in the sky may already have died out. We are seeing what used to be millions or billions of years ago…We see the past.

Nebula PlanetsStars Other solar bodies Solar systemsStar ClustersGalaxiesGalaxy Clusters Galaxy Superclusters The UniverseQuasars

Nebula A massive cloud of gas, dust and heat The birthplace of stars and planets Stars A very large burning ball of gas Stars do nuclear fusion (two small atoms fused to form larger atoms) and produce lots of energy Planets “cool bodies”, no nuclear fusion, no emission of light Planet means “wanderer” in Greek b/c wandered in sky among the stars Small Solar System Bodies Comets-frozen balls of gas only visible when near the sun Asteroids-small irregular objects of rock and ice Meteors = “shooting star” caused by asteroid coming into our atmosphere Meteorite – if outerspace rock makes it to Earth’s surface

Solar Systems An ordered group of objects orbiting a star (like our sun) Star Clusters 10,000 to several million gravitationally bound stars (2 types) Globular clusters are dense spherical shapes Open clusters are less dense (only 100 stars or so like Orion Nebula)

This image to the left is an example of a galaxy cluster The galaxies of HCG 87, about four hundred million light-years distant. The large edge-on spiral, the fuzzy elliptical galaxy immediately to its right, and the spiral near the top of the image are members of the group, while the small spiral galaxy exactly in the middle is a more distant background galaxy. Credit: NASA/ESA.HCG 87NASAESA Galaxy A giant mass of 100’s of billions of stars, nebulae, and interstellar gas and dust (3 types) Spiral (and bright) – like ours…THE Milky Way Galaxy or Andromeda Gal. Elliptical – most common and are dimmer Irregular – small and faint

Galaxy Clusters large groups of galaxies, often several hundred, with diameter of 10 million light years or moregalaxies We are part of “The Local Group” Cluster Quasars (special galaxy) QUAsi-StellAr Radio source Thought to be blasts of extreme amounts of energy emitted from supermassive blackhole center of a galaxy The brightest and most distant, thus oldest, objects in sky

Galaxy SuperClusters Probably the largest objects in the universe We are in the Virgo supercluster The Universe Defined as everything that physically exists (including dark matter which is not visible) Made of over 100 billion galaxies, and “born” from the big bang about 14 billions years ago

Dark matter the hypothetical matter that we can not see, yet is thought to account for the vast majority of the mass in the observable universe The observed phenomena which imply the presence of dark matter include the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster.