Astronomy100 Final- Scientific Method – 2o The universe functions logically All actions have an effect, cause and effecto Every location in the universe obeys the same physical principleso A scientific must be able to be tested by any scientisto An astronomer has a hypothesiso Astronomer makes observations to gather evidenceo If evidence supports, it may be correct. If it disproves it, it is wrongo If hypothesis is tested many times and all evidence supports it, the astronomers begin to rely on it and call it a theory- How do we know the Earth rotates? Part 1 – 3 o Patterns out of stars in order to make sense of the sky – constellationso Entire sky is split up into constellationso Astronomers use constellations as reference points to communicate what part of the sky they are observingo Picture the sky as an upside down bowl, with stars on ito Earth is surrounded by an imaginary sphere called the celestial sphere Imagine that the stars and sun are attached to the sphere Over the course of one night/day, we see the stars and sun move, so we can imagine the sphere is rotatingo The stars and the sun generally rise in the east and set in the west over 1 night/dayo Some stars are always above the horizon and always visible – circumpolar stars Appear to circle around the north staro Some stars are never visible and always below the horizon- How do we know the Earth rotates? Part 2 – 4 o A pendulum always swings in the same plane (back and forth in the same direction) o Motion of pendulums ahs been tested extensively with experiments sothat scientists fully understand ito If a pendulum is set up on a spinning object, the pendulum will keep swinging in the same direction, even though its support is spinningo The pendulum might appear to be changing direction, but its because the support is spinningo A Foucault pendulum is designed to swing for a long time and is usually used to show that the Earth is rotating When it starts, it will gradually appear to change direction It isn’t changing direction, the Earth’s surface is rotating underneath it- How do we know the Moon orbits the Earth? – 5o Each day the moon rises about 50 minutes than the day beforeo Each day the phase of the moon changes a little bito Phases of the moon New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent, new The phases of the moon repeat about once a month The phases of the moon are caused by the position of the moonin space and our point of view from earth The half of the moon facing the sun is always lit up The moon is usually in a location where it cannot be in the Earth’s shadow The moon’s orbit is slightly tilted, so the moon usually passes above or below the earth’s shadow The phases of the moon are not caused by the earth’s shadow When the moon does pass through the earth’s shadow, we observe a lunar eclipse Sometimes the Earth passes through the Moon’s shadow and we see a solar eclipse- How do we know the Earth orbits the Sun? – 6 o As we observed the planetarium program, we see different stars and constellations in the sky at different times of the year: seasonal starso The fact that we see seasonal stars does not prove the earth orbits the suno Apparent shift in position is called parallaxo Stellar parallax is the apparent shift in the position of nearby stars caused by the Earth orbiting the Suno As the earth orbits the sun, nearby stars change position slightly over 1 year- How do we know other planets orbit the Sun? – 7 o Over the course of a day/night each planet rises and sets along with the starso If we observe the planets over weeks and months, we can see that they move compared to the starso Most of the time, the planets move eastward compared to the stars: prograde motiono The planets all move along a path called the ecliptic which passes through the zodiac constellationso The planets rise and set each day because the earth is rotatingo The planets move eastward because they are moving through spaceo The planets repeat their motion following the ecliptic over years because they are orbiting the suno Because they all follow the same path though the sky, they must be orbiting the sun in the same plane- Why do the planets stay in orbit around the Sun? Part 1 – 8o In the 1600s, Isaac Newton was the first person to realize that the physical laws on the Earth must apply to everything in the universeo Mass: the amount of matter an object haso Velocity: an objects speed and direction of motiono Acceleration: a change in an object’s velocityo Force: anything that causes an object to accelerateo Newton experimented with the motion of objects and put the principles he learned into 3 laws An object moves at a constant velocity unless a net force acts tochange its speed or direction- If an object isn’t moving then it wont start moving by itself- If an object is moving, it will move with constant velocity (same speed and direction)- Describes the property of matter called inertia: the tendency of matter to not change velocity unless force acts on it Force= mass x acceleration, F=ma- If a force does act on an object, then the object will accelerate- The amount of acceleration an object has is proportional to the amount of force acting on ito a=F/m- The amount of acceleration an object has is inversely proportional to its mass For any force, there is always an equal and opposite reaction force- Equal in force and opposite in direction- Why do the planets stay in orbit around the Sun? Part 2 – 9 o The more matter an object has, the greater the gravitational force thatit exerts on other objectso The farther apart two objects are, the weaker the gravitational between them iso F=GM1M2/d^2 G = 7x10^-11 Nm^2/kg^2 M1 = mass of the first object M2 = mass of the second object D = distance between the centers of objects Newton = 1kgm/s^2o If more than 2 objects are involved, each object feels a net gravitational forceo The gravitational force between all the bits of material in a large object holds it togethero Large objects like moons, planets, and stars are held together by gravityo Groups of individual objects, such as those in our solar system or our galaxy, are held together by the gravitational force between all objectso Smaller objects, such as boulders, people, cars, trees, and so on are notheld together by the force of gravityo The gravitational force