February 1, 2011From the last LectureThe distances, sizes, time and temps in astronomy extend well outside your normal experience.Temps: astronomical objects can be much hotter and colder than normally experienced by you. Astronomers use the Kelvin temp scale to measure temps…a temp is so-many Kelvins or K.Distances and LightLast time we talked about light-travel as convenient measure for distance in astronomy.Distance= speed x time-travelingIn our case: Distance= speed-of-light x timeThe speed of light is a universal constant (186,000 miles per second or 3 x 10^5 km/second)Light travels very fast but it does take time to travel from one spot to anotherSo the light that you see now left the object a time in the past which is the light travel time to the objectDistance is a time-travel machine in astronomyUnitsSize: kilometers (km); meters (m); microns (10^-6Distance: meters (m); kilometers (km)Velocity:Distances: Astronomical Unit (AU = Eath-Sun distance)Light years; parsecs (pc;Kilo-parsecs (kpc = 10^3 pc);Mega-parsecs (Mpc = 10^6 pc)Mass: solar mass = mass relative to the mass of our sun1 solar mass = 1.99 x 10^30 kgScientific MethodHidden Assumptions in the Scientific Method:There exists an objective, knowable Universe that is the same for everyoneThe same physical laws apply throughout the UniverseThe same physical laws are equally valid at different times in the UniverseHallmarks of Science1) Science seeks explanations for observed phenomena that rely solely on natural causes2) Science prefers solutions which explain the observations in the simplest way that are consistent with the data3) A scientific model must make testable predictions about natural phenomena that can cause us to revise or abandon the model if the predictions do not agree with observationsMeasurement UncertaintyNo experiment or observation can measure a value with perfect accuracyKnowing this can be essential for hypothesis in scientific method.The Celestial SphereThe Celestial Sphere is based on how the sky looks from the surface of the EarthThe Earth is at the center and the sphere rotates around the EarthThe North and South Celestial poles are the projections of the Earth’s polesThe Celestial Equator is the projection of the Earth’s equatorThe path of the Sun on the Celestial Sphere is the eclipticThe Ecliptic is titled at an angle of 23.5 degrees relative to the Celestial EquatorThe Vernal Equinox is where the Sun crosses the Celestial Equator traveling northward – the beginning is spring in the northern hemisphere.The Autumnal Equinox is where the Sun crosses the equator traveling south – fall **QUESTION FOR TEST**The point when the sun is furthest north is the Summer Solstice – summer (23.5 north latitude)The point when the sun is furthest south is the Winter Solstice (23.5 south latitude)From the point on the standing on the Earth, the Sun’s path on the sky changes with the seasonsZenith = point directly over your headMeridian = great circle going from S to N through your zenithDefining the DayAre the Solar and Sidereal days the same? NO!The Earth makes one more rotation each year with respect to the stars than it does with respect to the sun. Sidereal day is shorterSolar Day = 24 hoursSidereal Day = 23 hours 56 minutesA year is 366 Sidereal days…this was stressedFebruary 3, 2011Motions of the Earth-Moon-Sun SystemMoon orbits the Earth with a period of 29.5 daysNew Moon: Sun-Moon near each other. Always during the day. Moon sets before or soon after the sunWaxing Crescent: Moon rises a little after the sun1st Quarter: Moon rises 6 hours after the Sun. Moon high in the sky when Sun setsFull Moon: Moon opposite Sun on sky. Moon rises when Sun sets.3rd Quarter: Moon rises 6 hours before SunWaning Crescent: Moon rises a little before SunEclipses of the Moon occur when the Moon moves into the shadow of the EarthMoon moves through the shadow in about three hoursEclipses occur when the Earth is exactly on the path of light from the Sun to the moonThe Moon’s orbit is tilted about 5 degrees relative to the plane of the Earth’s orbit about the SunEclipses only happen when the alignment is perfect.The eclipse is seen from all parts of the Earth that can see the Moon at the time of the eclipseMoon moves through the shadow in about three hoursEclipses occur when the Earth is exactly on the path of light from the Sun to the moonTotal lunar eclipses occur on intervals of 5 months to a few yearsSolar Eclipses happen when the Moon moves between the Earth and the Sun and blocks the light from the SunThe shadow of the Moon moves across the Earth as the Moon move in orbit about the EarthTotal eclipses happens only over a small area which moves across the Earth. Partial eclipse happens over a lagers area. Totality lasts a few minutes **TEST QUESTION, FULL MOON ECLIPSE SHIT**In total eclipses, the Moon sometimes covers the entire Sun; other times the edge of the Sun remains as a bright ring around the moon during the “total” eclipse. Why? The moons orbit is not a perfectly circular; therefore, the distance from moon to Earth is not always constant.We always see the same face of the moon as it orbits earth; rotation of moon is locked gravity to earth (face-locked)Why is it face-locked? The gravitational pull of the Earth raises “tides in the shape of the Moon which over hundreds of millions of years slowed down the rotation of Moon until it exactly matched its orbitFebruary 8, 2011The Geocentric ViewThe Earth is the center of the Universe and all bodies are as they appear relative to usThe stars are unchanging set of lights that revolve around the Earth – like in the Celestial SphereIt was also recognized that the Moon and some ‘stars’ moved against the background multitude of stars (the moving ‘stars’ we now know are planets)The observation of the movement of the Moon, Sun and “planets” produced the first complication in the Geocentric view – all celestial objects could not be on a single rotating sphereGeocentric ideas were developed in detail by the Greeks in 500-300 BCThe changing phases of the Moon gives the clue that the Moon was on a sphere closer then the Sun. The size of the Moon makes it a natural to be closer then the other objectsThe ordering of the planets reflected their observed speed on the skyAristotle believed that there were 55 concentric spheres to which the celestial objects were attached with Earth as centerAristarchus proposed that the Earth went around