HIST 2620 1nd Edition Lecture 3 Outline of Last Lecture I Review Chapter 1 II Scientific method III Hypothesis theory and law IV Scientific Models V Constellations VI Magnitude scale VII Celestial Sphere Outline of Current Lecture I Solar day vs Sidereal day II The Ecliptic III Seasons Current Lecture I II Solar day vs Sidereal day solar day exceeds sidereal day by about 4 minutes objects in the sky rise about 4 minutes earlier each night o If Sirius rises at 8pm tonight what time witll it rise tomorrow 4 minutes earlier o A month from now 4 minutes per day x 30 days is 120 minutes 6pm o 6 months from now 2 hr month so 8am Over the course of a year we don t see star in the sky because the sun is so much closer to us We see the stars that are on the oppositie side of the sun this is because of our orbital motion around the sun that gives us the yearly rotation of WHEN we see constellations The Ecliptic The sun Sun orbital plane If the sun appears to move around the earth every 24 hours but the sun moves around the background stars They move less than 24hrs 4 minutes These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III short The zodiac constellations are the ones that are along the path of the sun on the celestial sphere Geocentric model because its based on the stars o When the is behind then the opposite side includes the constellations that can be seen The sun The ecliptic is titled to the celestial equator You might notice that the earth is tilted at 23 5 degrees toward the sun in the celestial sphere the sun goes above and below the celestial equator o Earth isn t the only planet with a tilt Jupiter is moving with its rotation access in the ecliptic Venus s obliquity is 180 so it rotates in the opposite It s south would then be north etc If earth s rotation access were perpendicular the ecliptic celestial equator Because the sun would go around the equator and the ecliptic rather than above and below the equator Seasons Is it the campfire effect NO o When the earth is closer to the sun the surface is warmer When the earth is tilted toward the sun it is closer to the sun and the surface is warmer Earth is CLOSER to the sun during winter The Seasons are ACTUALLY caused ONLY by a varying angle of incidence of the sun s rays Heating by the sun THE MORE DIERECT THE MORE HEAT How do you end up tilted towards or away from the sun The tilt is always towards Polaris So the fact that the pole star stays constant means that the rotation axis in space means its fixed Seasons are the result of a varying angle of incidence This causes an equinox day night at some points This is when no part of the earth at the point is when the earth is not pointing towards or away from the sun In the Arctic circle never rotate into daylight at north pole while south pole never rotate into night How long is the sun above the horizon each day o Depends on how much of the path is on daytime nighttime path Tilted away long nights shorter days vice versa Sun up longer in summer shorter in winter It also changes WHERE the sun rises and sets Winter fall hemisphere is rotated away from the sun so it will appear to rise and set south of due east west o Equatorial regions always have the sun passing through their zenith on the equinox On a pole the sun was never very high above the ecliptic Times of total and complete darkness in winter and times of total and complete daylight in the summer due to the sun never rising above the ecliptic Questions o In the quatorial regions these areas almost always have the sun nearly overhead The poles in the same sense are always colder because the angle of the sunlight even if totally upright Even if we had the same amount of daylight night it s really about the ANGLE of the sun s rays ALWAYS more heating at the equator o If earth were totally upright how would the seasons be different With less angle less seasonal variations and more equal day nights IF EARTH WERE more angle 90 then the sun would bring more drastic seasons Uranus 84 years around the sun so is total darkness with extreme seasonal variations etc o When sun is furthest sepearation north or south of celestial equator Sun stand If we ploted the suns path the positon of the sun would changeover the year The figure 8 pattern greated is an analemma What causes the seasons o Sun is up for more hours and in the summer the angle of the sun is more direct Precession o The earth precesses wobbles like a top take 26 000 years to follow the circular pattern that the earth wobbles on So back in 33 000 the pole star was Thuman It processes because the tugging of the earth isn t always the same We have a large moon orbiting the moon actually stabilizes our precession This is also the reason why astrology is not followed because the position of the stars changes constantly In 12 000 years from now Vegas will be the pole o The timing when the sun crosses the celestial equator will have Orion in the summer Not a new idea that earth processes New star charts published each 7 years due to its changing axis o Another effect of precession causes a shift in the intersection point of the ecliptic and the celestial equator The yearly seasonal affects on the earth s climate If its tilting a slightly different direction then you will have different heating in seasons You are not pointing in the same direction so the timing of the seasons will also change to precession The Milankovitch Cycles refers to the reason for the Ice Age could be due to the changes in the eccentricity of the earth that varies with time All of these changes can be sued to product long seasonal cycles on earth Astronomical influence on earth s climates o Not too much of a difference bewrteen the predicted temps by the milankovitch theory But that doesn t mean its right just because of correlation BUT it is to be considered These variations cant be controlled Motion of the planets o The planets are orbiting the sun almost exactlt in the plane of the ecliptic Te speed wit hwhich they move around the sun is different Closer move faster around the sun than those that are farther away The moon is also moving the earth in the same sense that the earth is orbiting the sun These will be further discussed in chapeter 19 o All outer planets generally appear to move eastward along …