Powers-of-ten NotationNumbers in astronomy can be well… astronomically big (or small)This format is used to abbreviate numbers. For very large numbers this saves a lot of spaceFormat(+/-)a.bc x 10^(+/-)da is a digit from 1 to 9 bc ranges from 00 to 99 and the exponent d is any integerThe average distance between the Sun and the Earth is called:The Astronomical Unit=A.U.This is ~ equal to 150,000,000 kilometers (1.50 x 10^8 km)Or ~93,000,000 miles (9.30x10^7)For small numbers use a minus sing in front of the exponent0.0000000067 (6.70x10^-9)In this course, two decimal places in a result are usually all that are neededMetric SystemWhat do we mean by the size if an object?Distance across an objectFundamental unit of distanceMeter (about 1 yard)1 kilometer= 1,000 m ~0.6 mi.Asteroid CeresDiameter about 1,000 km x 0.6 miles ~600 miles1 km1 cm =1 centimeter ~0.4 inch1 mm = 1 millimeterFundamental unit of massKilogram ~ 2.2 poundsWhen we consider how much material an object contains we talk about its massThis is not the same as weightWeight depends on where the object is. An object on the surface of the Moon will have 1/6 the weight it has on the Earth, but will have the same mass.There are other Fundamental unitsDistance Scales and/ or Powers of Ten VideoHow Big is The UniverseWhen we make scale models we can envision just how truly vast it is!Chapter 1: Discovering the Night SkyIllusions in the night skyNight sky is filled with apparent patters of stars called “constellations”Stars aren’t at the same distance, they are millions of miles separate from each other in spaceStars are only close together in terms of angular separation not physical separation (distance)Constellations are named in honor of people, animals, objectsThere are 88 divisions in the night sky that have a constellation in each sectionNaming of StarsGiven names for the brightest stars: Vega, Regulus, BetelgeuseGreek-letter designations for the brightest and intermediately bright stars: alpha Lyrae, a Leonis, alpha OrionisCatalog numbers for the brightest stars, intermediately bright, and dimmer stars: (HR 7001, BD +122149, HD 39801)The Celestial Sphere (CS)On a clear night, an observer seems to be at the center of a vast dome or sphere with black or gray interior, which is sprinkled with stars, planets.Illusion caused by the inability to interpret the distances to points of light. Although not real, it is used by astronomers to locate objects in the skyCelestial Equator (CE)= Imaginary line on CS directly above Earth’s EquatorNorth Celestial Pole (NCP)= imaginary point directly above (at the Zenith) Earths North Pole (Polaris is quite near to it)South Celestial Pole (SCP)= Imaginary point directly above Earths South Pole (No bright star is near to it)The CS appears to rotate around the earth (going West) once in 24 hoursThis is the illusion that causes the Sun, Moon, planets, stars to appear to rise in the East and set in the WestThe actual cause is the Earth’s rotation toward the East. (Rotate= to spin on its axis)The annual apparent Eastward motion of the Sun along the inside of the CSCause: the earth revolves around the Sun. (Revolve= to orbit another object)Ecliptic= name of Sun’s annual path on the CS (this is also the name of plane of the Earth’s orbit around the Sun)This annual motion of the Earth also causes stars to rise ~4 minutes earlier each night. There is an annual “Parade of Constellations”The Constellations of the ZodiacThe sun appears to move through the zodiac constellations along the eclipticZodiac= the band of 12 or 13 constellations centered on the Ecliptic. The Sun spends ~1 month in eachThe bright planets can always be seen within the boundaries of the ZodiacThere orbits are nearly in the plane of the eclipticTo locate faint objects in the sky we use a coordinate or angle systemEquatorial CoordinatesDeclination (similar to latitude on earth)Right Ascension (like longitude on Earth)Daily PathsThe paths of the sun, moon, planets, stars, and etc. depends on latitudeThe North PoleAll objects move in paths parallel to the horizon. The altitude of the NCP is 90At equatorAll objects rise and set perpendicular to the horizon. The altitude of the NCP is 0At 37 NAll objects rise at an angle with respect to the eastern horizon and set at an angle on the western horizon. The Altitude of the NCP is 37You can measure the latitude by measuring the altitude of Polaris above your northern horizonYour latitude = Altitude of NCPCircumpolar StarsTheses are stars that never rise and never setAt the north and south poles the entire sky (1/2 of the CS) is circumpolar. At the Equator none of the sky is circumpolarAt Springfield’s latitude a small section of the northern sky is circumpolarSeasonsEarths rotational axis is tilted ~23.5 degrees with respect to the perpendicular to its orbit; this is what causes seasons on earthBecause of this tilt:Duration of daylight varies annuallyAt our latitude:Sun above horizon ~15 hrs- Summer~ 9 hrs- WinterAngle sunlight strikes surface variesAt our latitude:Suns altitude at noon ~77 degrees Summer~30 degrees WinterCurrent season in Southern Hemisphere is always opposite oursThe season have nothing to do with the changing distance between the Sun and the Earth, nor with any change in the Sun’s heat outputPhases of the MoonWhen the sun shines on any sphere there is always a sunlit hemisphere and an unlit hemisphereThus phases are caused as the moon orbits the earth and we see a changing portion of the sunlit sideThe phases of the moon have nothing to do with the Earth’s shadowThe other planets in our solar system go through phases as seen through a telescope from the earththe phases shapes of Mercury and Venus are quite obvious, but for outer planets the only phases are (slightly) gibbous and fullThe view of Earth from the Moon:SizeThe earth is four times bigger than the moonColorThe earth have the blues, greens, browns, and other colors we haveBrightnessThe earth would be much brighter than the moonPhasesThere would be phases of earth opposite of what we see the moon havePosition in the lunar skyDepending on where you are standing the earth would be above, below, or anywhere elseSynodic vs. SiderealSynodic:With respect the sunSiderealWith respect to a starFor the moons orbit of Earth:Synodic period ~29 ½ days (same as period of cycle of phases)Sidereal period ~27 1/3 daysThe moons rotation (spin) is synchronized to its revolution (orbit)TimeTime