ASTR 101 September 3 Appearance is deceiving Earth is not the center of the universe Solar System consists of sun planets their moons and countless smaller objects including rocky asteroids and icy comments Sun is a star Milky Way Galaxy huge disk shape collection of stars Galaxy great island of stars in space containing from a few hundred million to a trillion or more stars Galaxy Cluster groups of galaxies with more than a few dozen members o Milky way is in a cluster of 40 called a local group Space clusters region in which galaxies and galaxy clusters are tightly packed Universe sum total of all matter and energy encompassing the super clusters and voids and everything within them AU astronomical unit Earth s average distance from the sun about 150 million kilometers o Used to describe distance within our solar system ly light year distance light can travel in a year about 1 trillion kilometers o This distance can be found by multiplying the speed of light by seconds per year o Used to describe distances of stars and galaxies o Because light takes time to travel you see some planets stars in the past thus the farther distance of the star the farther in the past we look Observable universe is the portion of the entire universe that we can observe 14 billion light years makes the boundaries o Most likely only a tiny piece of the actual universe Remember a solar system is a single star system and a galaxy is a billion star system The number of stars in our observable universe is equal to the number of grains of sand on all the beaches on Earth September 5 Science is difficult to define because not all science works the same way Hypothesis educated guess allows you to make simple predictions Make observation ask a question suggest a hypothesis make prediction perform a test experiment or additional observations o If test does not support hypothesis revise hypothesis or make a new o If test supports hypothesis make additional predictions and test them one Three Basic Hallmarks of Science 1 Seeks explanation for observed phenomena 2 Progresses through creation and testing of models of nature that explains the observation as simply as possible 3 Makes testable predictions about natural phenomena When a powerful yet simple model makes predictions that survive repeated and varied testing scientists elevate its status theory Science ultimately provides a means of bringing people to agreement topics that can bring subjected to scientific study Constellation a region of the sky with ell defined borders familiar patterns of stars help us locate them o Collectively the constellations fill the celestial sphere o Celestial sphere is a useful illusion because it allows us to map the sky as seen from earth North celestial pole NCP directly over earths north pole South celestial pole SCP directly over earths south pole Celestial equator projection of Earths equator into space makes a complete circle around celestial sphere Ecliptic yearly path of the sun around celestial sphere The suns annual path in relation to constellations NOT daily path in the local sky o The earth rotates from West to East making the celestial sphere to APPEAR to rotate from east to west Latitude describes the angle your zenith makes with the equator and determines the angle at which your horizon slices through the celestial pole Ones latitude determines the portion of the celestial sky you see and the stars you ll see As we orbit the sun over the course of the year the sun appears to move against the background of constellations on the celestial sphere Sun gradually moves east but we can t tell because the sun and stars aren t out at the same time The suns apparent location along the ecliptic determines which constellations we see at night September 10 Common Misconception the moon is above the horizon as often in daytime as at night but its light is often drowned out by sunlight o First quarter moon is easy to spot in the late afternoon as it rises through the eastern sky o Third quarter moon is visible in the morning as it heads toward the western horizon Waxing increasing Wanning decreasing Before and after new moon crescent Before and after full moon gibbous Moon has synchronous rotation thus we only see one side of the moon Throughout astronomy angular measurements are used to describe the location of objects in the sky o Angular distance angle that appears to separate objects in the sky o For precise astronomical measurements we divide every 60 degrees into acrminutes and subdivide every acrminute into 60 arcseconds Seasons are caused by the tilt of the earth s axis which in turn causes the sun path and the intensity of sunlight to vary during the year Boundary between Earth and Sky horizons Point directly overhead zenith Meridian is an imaginary half circle stretching form the horizon due south through the zenith to the horizon in the north sky One can pinpoint the position of any object in the sky by stating its direction along the horizon and its altitude above the horizon The sun will only reach the zenith for locations within the tropics and between 23 5 degrees N and 23 5 degrees S Season Changes o Earths axis remains pointed to the North Star at all times o The orientation of the axis relative to the Sun changes over the course of each orbit o N Hemi is tipped toward the sun in June and away in December o N Hemi sun at higher angle in June thus higher concentrated rays which makes it warmer as well as the sun follows a longer higher path thus longer days o distance from sun has no effect on seasons Summer June Solstice moment when the N hemisphere is tipped most directly toward the Sun and receives the most direct sunlight Winter Dec Solstice N hemisphere receives the least direct sunlight Spring March Equinox moment when the N Hemi goes from being tipped slightly away from the sun to slightly toward Fall Sept Equinox N Hemi starts to be tipped away from the sun The sun reaches its highest point each day when it crosses the meridian at noon however unless you live in the tropics the sun is never directly overhead September 12 Moon and Earth cast shadows in sunlight called eclipses o Lunar occurs when Earth lies directly between Sun and Moon so o Solar when the moon lies directly between Sun and Earth so the Earth s shadow falls on the Moon moons shadow falls on the Earth People living within the area covered by moon s shadow will see the Sun blocked Due to the inclination of its orbit the moon spends most