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Welcome! PH104 Descriptive Astronomy MWF 1:00 – 1:50 pm Weniger 151 Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Today’s Slides • • • • • • • Course Intro Some Logistics What IS astronomy? The Planetary Neighborhood Some New Units of Measure The Night Sky Textbook units covered: 1, 2, and 5 PH104 Descriptive Astronomy • Instructor Info – – – – Jim Ketter. Feel free to call me Jim. Office: WNGR 315 Office Hours: MW 9:00-9:50 You are welcome to stop by at other times or make an appointment if you need to see me at other times. – Email: [email protected] • Lab Instructors: Kristin Dexter, Jake Goodwin, Jeff Holmes, Tim Surber Contact information is posted on the PH104 website: www.physics.oregonstate.edu/ph104 PH104 Descriptive Astronomy • Most course information will be located at the course website: www.physics.oregonstate.edu/ph104 • Syllabus and schedule will not be handed out on paper. • Overview of website info… • Exam grades (only) will be posted on Blackboard. • Course counts as a baccalaureate core laboratory course. • Course Grade (details in syllabus) depends on: – Labs and Prelabs (Lab Manual online) – In-class participation (via Qwizdom) – Exams (2 Midterms and a Comprehensive Final) PH104 Descriptive Astronomy • Labs – All labs are held in WNGR 206. – You are scheduled in one 2-hour lab per week on either Tuesday or Thursday. – Completion of lab is mandatory for passing this course. • Exams – There will be two midterm exams, one in week 4 and the second in week 8. There is also a final, comprehensive exam (covers whole term). PH104 Descriptive Astronomy • Labs and Prelabs – Prelabs must be turned in at the start of your scheduled lab (as you enter lab.) – Both Prelabs and Labs are in the lab manual. – Lab exercises will be completed and checked off during the scheduled lab section. – Do not move around to different labs without discussing with me and the TA. – 7 of 8 labs must be completed in order to pass the course. – There are no make-up labs. Don’t miss lab. PH104 Descriptive Astronomy • Labs and Prelabs continued – You must score 70% or better on a prelab in order for it to be considered a passing grade. – You must satisfactorily complete 70% or more of a lab in order for it to be considered a passing grade. The TA will make this assessment during the lab. – You must successfully complete (pass) 7 of the 8 prelabs and 7 of the 8 labs in order to pass the course, regardless of your other scores. PH104 Descriptive Astronomy • In-class Participation – Class participation will be augmented via the Qwizdom “clicker” system. – Participation requires purchase of Qwizdom unit. • Night Viewing – There will be opportunities for some night sky viewing using telescopes atop beautiful Weniger Hall. – Attendance is optional but is the one place in the course where extra credit points are available. – Depends on weather. Sessions will be announced. PH104 Descriptive Astronomy • What Astronomy isn’t. – It is not astrology. Might have been once but… – It isn’t memorizing names of stars and constellations. – It isn’t laying around looking at the sky all night. • What Astronomy is. – – – – It’s a start at looking at the amazing universe we live in. It’s a look at how we know the things we know. It’s a look at the nature of science. It’s a look at the historical development of our understanding of the universe around us. The Earth • The Earth is a planet, a body in orbit around a star (The Sun) • Radius: 6371 km (3909 miles) • Mass: around 6 billion trillion tons • Actual value: 5,970,000,000,000,000,000,000,000 kg • Too many zeros! Use 5.97 1024 kg, instead! Metric System •Easier to use (everything is a factor of 10!) •More in Unit 3… The Moon • The Moon is a satellite, a body orbiting a planet – Rocky world, littered with craters • Bombarded by meteors • Where are the Earth’s craters? – Smaller than the Earth • Less than 1/80 the mass • ¼ the diameter of Earth – Small, so cooled quickly! – Cold, airless and lifeless The Planets Why are they so different? How did they get this way? ←Oops! Pluto! • Wide variety of planets in our Solar System: – – – – Rocky, hot and airless worlds. Gas giants and ringed wonders. Cold planets of blue methane. Tiny icy bodies. At relative size (NOT distance) The Sun • The Sun is a star, a huge ball of gas held together by gravity and generating light through thermonuclear reactions. • Source of all energy in the Solar System, on our planet. (Except…) • 100x wider than the Earth, 1,000,000x larger, and 300,000x as massive! • Old, yet still young… – 4 billion years old. – Will last another 5 or 6 billion years. The Solar System • • • • Planets, asteroids, comets and dust all held together by the Sun’s gravity. Everything goes around the Sun on elliptical paths called orbits. All orbits lie in (nearly) the same plane, like peas rolling around on a saucer. Too big to describe using meters – we need something more convenient. A convenient measure – the Astronomical Unit • It is convenient to measure planetary distances using the Astronomical Unit, or AU. • 1 AU = average distance between the Earth and the Sun. • 1 AU ~ 150 million km ~ 93 million miles. Some approximate, average orbital radii sizes: • Mercury: 0.4 AU • Mars: 1.5 AU • Saturn: 10 AU • Pluto: 40 AU A New Measure of Distance • Stars in our Milky Way galaxy are very far apart! – Nearest star is 40 trillion km away – too large to imagine! – This is hundreds of thousands of AU. Whoa! Still too big. – Light travels 10 trillion km in one year, so we’ll use the light year (ly) as a common measure of distance in space. – It takes light 4.1 years to travel from Proxima Centauri to Earth, so the distance from here to that star is 4.1 ly. Getting to Know the Neighborhood • The Universe is “clumpy” – galaxies tend to cluster together because of gravity. Central region of the Virgo Cluster – Our immediate neighborhood is called the Local Group, a cluster of around 3 dozen galaxies, 3 million light years across. – The Local Group is part of the Virgo Cluster, a collection of smaller clusters of galaxies. – Superclusters: still larger collections of galactic clusters. – The Universe – simply everything! Outward to the Universe! A hundred years ago, our galaxy was believed to be the entire universe. 50 years ago, they believe there might be dozens or hundreds of galaxies out there. Today, we know there are (at least) billions of galaxies within our universe! The Celestial Sphere I • A useful model of the sky is called the Celestial Sphere. • It is not real – it is simply a tool for understanding and visualizing our sky. • It was “reality” for the ancients. • Stars in the universe are located at various distances from Earth, but can be imagined as lying on a sphere, with the Earth at its center. • This sphere appears to rotate around the Earth, giving the impression that stars rise and set. The Celestial Sphere II • Important Terms – Zenith: The point directly overhead on the celestial sphere (CS). – Nadir: The point opposite the zenith on the celestial sphere. – North or south celestial pole: The point around which the stars appear to rotate. – Celestial Equator: An extension of the Earth’s equator expanded out to the surface of the CS. – Horizon: The lower edge of the visible CS. Constellations and Asterisms • • • The human brain is very good at recognizing • patterns. People thousands of years ago identified and named patterns of stars on the celestial sphere. The names of these patterns have their origins in mythology from different societies • from all over the globe. Sometimes hard/impossible to see. Requires an active imagination sometimes! These areas are called constellations. – 88 internationally recognized constellations, covering the entire sky. – Star names frequently include the name of the constellation in which they are located. Just some pattern of stars is not a constellation – these are called asterisms. – Big Dipper (of Ursa Major) – The Teapot (of Sagittarius) Skywatching • Under dark skies, you can see thousands of stars. There are some stars and constellations, however, that you can only see from northern or southern latitudes. • Constellations that never set (but simply circle around the Celestial poles) are called circumpolar constellations. • Skywatchers at our latitude in the southern hemisphere never see our circumpolar stars (here in the North). And vice versa… Finding Our Way Around • Finding your way around the celestial sphere is similar to finding your way around on Earth. – The CS is divided by lines of declination (running East-West) and lines of right ascension (running North-South). – Comparable to lines of latitude and longitude, respectively. – Stars can be located on the CS using their coordinates in this system, e.g., a star might be found at 4h RA, 40 degrees declination (similar again to latitude and longitude.)