Solar vs. Sidereal Day.

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Presentation transcript:

Solar vs. Sidereal Day

An Earth Day Sidereal Day: 23 hr 56 min 4 sec Motion relative to background stars Mean Solar Day: 24 hours The average time between meridian crossings of the Sun Apparent Solar Day: varies The actual time between the meridian crossings

Earth Orbits Sun

The Ecliptic

Tilt of Spin Axis

Ecliptic: Path of the Sun

The Equinoxes and Solstices Tilt of the spin axis is related to the seasons Effect of tilt on climate is not instantaneous

Ecliptic on the Celestial Sphere

An Earth Year Based on the motion of the Sun on the sky or the motion of Earth around the Sun Julian Year: 365.25 mean solar days. Used in calendars before 1582. Gregorian Year: 365.2425 mean solar days. Used in calendars today.

An Earth Year Sidereal Year: 365.256363 mean solar days. Defined by the motion relative to stars. Anomalistic Year: 365.259635 mean solar days. Defined as perihelion to perihelion. Tropical year: 365.242190 mean solar days. Defined from equinox to equinox. Thus, related to the seasons.

Sun Changes Declination

The Arctic and Tropical Regions How are the arctic and tropical regions defined? Can you answer this without looking at your books? Have you ever been to these regions?

Back to the North Pole

Cold Arctic Regions

Land of the Midnight Sun

Back to the Equator

Tropical Heat In the Tropics, Sun is always close to zenith In the Tropics, the sun reaches the Zenith at some point in the year Lots of heating due to sunlight