Measuring the Earth's Basic Properties and Magnetic Field - Prof. Roger B. Culver, Study notes of Astronomy

Download Measuring the Earth's Basic Properties and Magnetic Field - Prof. Roger B. Culver and more Study notes Astronomy in PDF only on Docsity! March 23rd, 2012 Earth Basic properties 1/ Mass of the earth = 6 x 1024 kg 2/ Radius of the earth = 6,400km Eratosthenes ~200BC noticed that on the first day of summer: sunlight is perfectly perpendicular to Seyene and forms a 7 deegree angular with Alexandria => radius of the earth. Seyene – Alexandria = 500 stadia  500 stadia / 7 degree = circumference of the earth/360 degree  Circumference of the earth = ~ 250,000 stadia = 25,000 miles = 40,000km 3/ Density = mass per unit volume (measured in g/cm3 or kg/m3) Typical ice: 1.0 g/cm3 or 1,000kg/m3 Typical rock: 3.0 g/cm3 or 3,000 kg/m3 Typical metal: 8.0 g/cm3 or 8,000 kg/m3 Mean density = total mass/ total volume Assume that all objects are spherical in shape => volume of a sphere = 4 3 π R3 Mean density of the earth = ~5,500kg/m3 Earth is composition of rock and metal (denser than rock but lighter than metals). Mean density of surface material = 3,300kg/m3 (mostly made up of rocks). Mean density of surface < mean density => mean density of the rest must be higher => the inner part must be denser. 4/ Magnetic field: Earth also has magnetic field. Common metals: Fe and Ni (nickel). Seismology tsunamis (mostly because of earthquakes) nuclear weapons – became banned --> tested underground. primary waves (travel thru both solids and liquids) secondary waves (do not travel through liquids) the crust is very complicated. Crust can be split up into plates. Plate tectonics -> earthquakes. Axis of rotation is no longer the axis of the magnetic field. Liquid outer core -> magnetic field. Other planets have magnetic fields.