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3.4 Nature of Science What are some hallmarks of science? How do you know you can believe a scientific result? What is the difference between a scientific theory and an “everyday theory”? Hypothesis Everyday meaning- a guess or assumption of almost any type Scientific meaning- a model that has been proposed to explain some observations, but that has not yet been rigorously confirmed. Model Everyday meaning- something you build, like a model airplane Scientific meaning- a representation of nature, sometimes using mathematics or computer simulations, that is intended to explain or predict observed phenomena. Example- A model of planetary motion can be used to calculate exactly where planets appear in our sky Theory Everyday meaning- speculation Scientific meaning- a particularly powerful model that has been so extensively tested and verified that we have extremely high confidence in its validity. Example- Einstein’s theory of relativity successfully explains a broad range of natural phenomena and has passed a great many tests of its validity. Law Everyday meaning- a rule created and enforced by the government Scientific meaning- a causal relationship between quantities that is Universal. It is usually expressed as an equation. Example- Newtons Law of Gravitation describes the force between two objects with mass (not moving close to the speed of light) Uncertainty Everyday meaning- ignorance Scientific meaning- a range of possible values around some central value Example- The measured age of our solar system is 4.55 billion years with an uncertainty of 0.02 billion years Astronomy vs. Astrology Astronomy is a science focused on learning about how stars, planets, and other celestial objects work. Astrology is a search for hidden influences on human lives based on the positions of planets and stars in the sky. *Astrological predictions are no more accurate than we should expect from pure chance* What are the differences between Astronomy and Astrology? What is the difference between the Solar System, the Milky Way Galaxy, and the Universe? What’s the difference between a planet and a star? What is a lightyear? Earth & Moon United of distance used for Earth and Moon is kilometers (km) 1 mile = 1.6 km The diameter of the Earth is 13,000 km The moon is smaller with only a diameter of 3,500 km The Earth rotates around its axis once everyday Solar System A central star or stars All the material that orbits the star (sun) *planets, their moons, asteroids, comets, etc..* Astronomical Unit (AU)- a unit of distance and a separation because the Earth and the Sun. Average distance between the Earth and the Sun 150 million km is the distance between the Earth and the Sun Earth orbits the Sun (revolves) once every year This motion causes different constellations at night Our solar system has larger, gaseous planets further out A “belt” of Pluto like objects at the edge Planets A moderately large, spherical object that obits a star Shines by reflected light May be rocky, icy, or gaseous in composition Our Sun is a Star A large, glowing ball of hot gas (plasma) that generates heat and light by nuclear fusion in its core, turning hydrogen into helium. Next closest star is Alpha Centauri A Galaxy is a collection of stars Our solar system is located in the outskirts of the Milky Way Galaxy From the sun to the outside of the Milky Way, it measures as 28,000 light years away. The milky way contains more than 200 billion stars Light year (ly) The distance light can travel in one year Unit of distance, not time Similar to saying, “Philly is two hours away.” *We think that the universe is 14 billion light years away* 1 light year = 9.5 trillion km = 60,000 AU Nearest star to our Solar System is Alpha Centauri -4.5 ly away Our sun and the other nearby stars have random motions, and orbits the galaxy every230 million years. Example to help remember- Ants on one horse of a carousel Ants = stars Carousel = Galaxy *Andromeda Galaxy and Milky Way are 2.5 million light years away* *They are on a collision course that will occur in a couple of billion years from now* GALAXIES IN GROUPS ORBIT EACH OTHER Galaxies are moving away from each other Observations: All galaxies outside our Local Group are moving away from us The more distant the galaxy, the faster it is racing away Conclusion: We live in an EXPANDING universe Galaxies are not getting larger The universe itself is expanding Galaxies are simply riding along as the fabric of space expands Earth’s orbit is nearly perfectly circular We experience no temperature change based on our distance from the sun This is because the Earths Rotational Axis is Tilted in respect to the sun Summer Solstice: Suns highest path Sun rises and sets at most extreme north of east and west Equinoxes: North & South are equal Sun rises precisely due east and sets precisely due west Winter Solstice: Suns Lowest Path