What time is it? Depends on where you are on the Earth! Time zones ensure that the noon is really noon, i.e. sun is at highest point To avoid confusion, use universal time (UT), the time at the meridian in Greenwich UT = EST + 5 hrs Daylight savings adds one hour in spring, so UT = EDT+ 4 hrs

The Time Zones Established to insure that sun is at highest point approximately at noon in the middle of the time zone

Daily and yearly motion intertwined Solar vs Siderial Day –Earth rotates in 23 h 56 m –also rotates around sun  needs 4 min. to “catch up” Consequence: stars rise 4 minutes earlier each night (or two hours per month, or 12 hours in ½ year)  After 1/2 year we see a completely different sky at night!

Carl Sagan Article: Baloney Detection Kit Occam's Razor Authorities do NOT carry a lot of weight Ask whether the hypothesis can be falsified Use MANY hypotheses to explain experimental facts There must be an independent confirmation of the facts Quantify!

Bacon: The subtlety of Nature is greater than the subtlety of argument. Often Nature is much weirder than we think (or are used to from our every day experiences) –At very large speeds (Relativity) –For very small objects (Quantum Mechanics) –For very dense objects (Black Holes) –Etc.

Fallacies of logic and rhetoric Ad hominem Non sequitur Appeal to ignorance Begging the question Observational selection  You may influence public opinion, but for scientific progress, all that matters is agreement with observations

Seasonal Motion Daily Rising and Setting: –Due to the rotation of the Earth around its axis –Period of rotation: 1 siderial day= 23 h 56 m 4.1 s –1 solar day (Noon to Noon) = 24 h –Stars rotate around the North Star – Polaris Seasonal Changes: –Monthly differences caused by Earth’s orbit around sun

The Zodiac throughout the Year Example: In Winter sun in Sagittarius, Gemini at night sky; in summer sun in Gemini, Sagittarius at night sky

Another Complication: Axis Tilt! The Earth’s rotation axis is tilted 23½ degrees with respect to the plane of its orbit around the sun (the ecliptic) It is fixed in space  sometimes we look “down” onto the ecliptic, sometimes “up” to it Path around sun Rotation axis

Activity: The Ecliptic Get out your activities book Form a group of 3-4 people Work on the questions Hand in a sheet of paper with the title of the activity and the names of the group members I’ll come around to help out !

The Seasons Change of seasons is a result of the tilt of the Earth’s rotation axis with respect to the plane of the ecliptic Sun, moon, planets run along the ecliptic

Animation TeacherTube video

Position of Ecliptic on the Celestial Sphere Earth axis is tilted w.r.t. ecliptic by 23 ½ degrees Equivalent: ecliptic is tilted by 23 ½ degrees w.r.t. equator!  Sun appears to be sometime above (e.g. summer solstice), sometimes below, and sometimes on the celestial equator

Zodiacal signs vs. Constellations -360/12=30, so each zodiacal sign is exactly 30 degrees “long” -0 degrees: Aries, 30 degrees: Taurus, 60 degrees: Gemini, 90 degrees: Cancer, etc. “Constellation” is a modern, well-defined term - Some constellations are big, some are small on the celestial sphere “Zodiacal sign” is the old way of dividing the year and the Sun’s path into 12 equal parts

Example The vernal equinox happens when the sun enters the zodiacal sign of Aries, but is actually located in the constellation of Pisces.