2About Science Scientific Measurement Size of Earth Size of the Moon Distance to the MoonDistance to the SunSize of the SunMathematics – The Language of ScienceScientific Methods
3Scientific Observation and Measurement How do you know whether the earth is flat or round?Is there any evidence that we can see from here?Where would be the best place to find this evidence?Evidence:Best place – on a large body of water – large, flat, level surfaceActivity – watch a boat sail out over the horizonObservations – (Evidence for a curve surface)Boat disappears sailing out – bottom firstBoat reappears sailing in – top firstClimbing to a higher vantage point brings the boat back into view.
4Other Observations The Sun and moon are round so why not the earth? The shadow of the earth on the surface of the moon during an eclipse of the moon showed that the surface of the earth was round.When did people first figure out the earth was round?~500 B.C. – Pythagoreans gave the similar shape reasoning (Induction argument)~300 B.C. – Aristotle used the disappearing boat argument.Educated people knew the earth was round in the 3rd century B.C. but didn’t know how to measure it.
5Size of EarthEratosthenes (Egyptian director of the Library at Alexandria) – 1st known calculation of the size of the earth.~235 B.C. Eratosthenes performed a measurement in Alexandria, Egypt that allowed him to calculate the radius of the earth.Somehow, Eratosthenes came to know about the well in Aswan (where the big dam is located), south of Alexandria, where the sun shines straight down to the bottom of the well at noon on the summer solstice
6At the Summer Solstice the earth’s axis is tilted 230 toward the sun At the Summer Solstice the earth’s axis is tilted 230 toward the sun. This brings the sun directly overhead in Aswan at noon on this day.While not directly south of Alexandria is wasn’t far off. (This would effect Eratosthenes’ ability to synchronize “noon” in both locations.)Aswan, AswanLat. 24:06:55N ( )Long. 33:00:47E ( )Alexandria, EgyptLat. 31o 7' NorthLong. 29o 54' EastAswan (anciently Syene) was on the Tropic of Cancer
7Equatorial circumference 40,075 km Surface area 510,900,000 sq. km Earth’s DimensionsPolar radius 6,356.6 kmEquatorial radius 6,378.2 kmEquatorial circumference 40,075 kmSurface area 510,900,000 sq. kmCaitlin,The correct tilt angle is 23 degrees 27 minutes,which is approximately degrees.David R. CookAtmospheric Research SectionEnvironmental Research DivisionArgonne National Laboratory
8Do the math hereOn Jun 22 – summer soltice – “only day the sun shone down the well at noon”This synchronized the measurement in Alexandriad/H = Shadow / Height = 1/8Angle ~7.20 or 7.2/360 = 1/50 of circumferenceThe distance from Alexandira to AswanD= 5000 statia ( =800km)Therefore Circumference = 5000 (50) = 250,000 stadia ( =40,000 km) or within 5% of the presently accepted value.
9Size of the MoonThe info needed to complete the next series of calculationsEarth radius Moon radius Moon distance Distance to Sun Sun diameterSize of moonUse the size of shadows during eclipses of the sun and MoonSolar Eclipse –Moon between Sun and Earth (Moon shadow on Earth)Lunar Eclipse –Earth between Moon and Sun (Earth shadow on Moon)
10Gives Earth diameter as 3.5 times Moon’s diameter Moon’s shadow on earth tapers to a point.It tapers by one moon diam.Hence the earth’s shadow must taper by one moon diam.During a lunar eclipse the earth’s shadow on the moon is 2.5 moon diam.Therefore the earth real diam is 3.5 x moon diam.Aristarchus in around 240 B.C. measured moon’s diameter and distance from earth.Presently accepted value of diam is 3640 km which is within 5% of Aristarchus’ value.Gives Earth diameter as 3.5 times Moon’s diameter
11Distance to the MoonSimilar triangles give: Moon diam / Moon distance = 1/110Early Greeks knew this.However, they needed Aristarchus’ measurement of the moon’s diameter to complete the calculation.
12Calculate Earth –Sun distance Distance to the SunThe coin on the window trick doesn’t work with the sun. The method needs a radius or diameter.It’s also dangerous to look at the sunMoon and sun subtend the same angle. This is observed.Remember the moon’s shadow tapered to a point during the solar eclipse.Same apparent size.Moon exactly covers sunHalf-lit moon determined geometry.Earth-moon distance knownMeasure angle xCalculate Earth –Sun distance
13Size of the Sun This is another way to determine the 1/110 ratio. Pin hole camera – with lenses and film (or CCD) you have today’s modern cameras.Camera Obscura – Camera (Room) Obscura (Dark)
14Mathematics – The Language of Science Science and mathematics came together some four centuries ago.Physics is based on concepts and mathematics provides an efficient, unambiguous means of expressing the relationship between theses concepts.We will be emphasizing the understanding of the concepts of Physics.But we will use equations for their ability to summarize relationships.
15MathematicsIn some cases we will use simple mathematics to estimate relative sizes to further aid in understanding the concepts.There is no math prerequisite for this course – all the math we will need will be developed right here.Similar trianglesRatiosEstimation techniquesA little trig
16Scientific Method Hypothesis Experiment Confirmation A Theory must explain currently known phenomena.A Theory must make predictions that can be tested.Goals:Theory as simple as possibleFew or no adjustable constants
17Scientific MethodCONCEPT - an abstract or generic idea generalized from particular instances.FACT - something that has actual existence <space exploration is now a fact>. Or an actual occurrence <prove the fact of damage>HYPOTHESIS implies insufficient evidence to provide more than a tentative explanation <a hypothesis explaining the extinction of the dinosaurs>.LAW implies a statement of order and relation in nature that has been found to be invariable under the same conditions <the law of gravitation>.THEORY - a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena <wave theory of light>
18Scientific MethodAs soon as a theory is established scientists start to investigate how far it can be stretched:smaller dimensions,larger dimensions,larger and smaller masses.
19Scientific Method Disagreements with established theory Initially attempt to modify the theory to fit in the new resultsTry to add new concepts to theoryDiscoveries are not always that orderly but can benefit from luck, accidents and a prepared mind.X-Rays were discovered when leaks in shielding exposed some nearby photographic plates.Cosmic Background Radiation was discovered when trying to eliminate electrical noise in telephone transmission equipment.
20The Rest of the Stuff The Scientific Attitude Rightness – Wrongness Honesty in Science.PseudoscienceScience, Art and ReligionA little person opinion from the authorScience and TechnologyRisk AssessmentPhysics – The Basic ScienceSome boasting by Hewitt
21Science and Technology Risk AssessmentPhysics – The Basic ScienceSome boasting by Hewitt