Earth-Sun Relationships Insolation, Day-Night and Seasons
Cosmic Connections: • Earth, Solar System and Beyond • 2. The Sun and Solar Radiation: • Insolation, Solar Energy • Inclinations and Movements of Earth: • Day-Night, Length of Day, Seasons, Latitudinal Zones
1. COSMIC CONNECTIONS: EARTH, SOLAR SYSTEM AND BEYOND What is the Earth’s relationships with the Sun and other heavenly bodies? How do phenomena like day and night, seasonal variations, climatic variations, and certain atmospheric anomalies happen? • Earth is almost entirely dependent on the Sun for its existence! • Earth, together with seven other planets, form our Sun’s • Solar System • Our Solar System comprises all celestial bodies surrounding and orbiting the SUN, (star) due to the star’s dominant mass and gravitational attraction. • And our Sun is one of an estimated 400 billion stars that make up our Galaxy – the Milky Way Galaxy.
All the stars that you see on a clear night are part of our • Milky Way Galaxy • Galaxies are sprawling space systems composed of countless clusters of stars, dusts and gases • Billions of galaxies – so far apart that measured in light years • (1 light year = 6 trillion miles; speed of light is 186,000 mps) • The closest galaxy to ours is 75,000 light years away • Some of these distant systems are similar to our own Milky Way Galaxy, while others are quite different • These are, then, our planet’s – Cosmic Connections
Earth and the Solar System • All the planets revolve around the Sun in the same direction • All the planets lie in a common plane – the Plane of the Ecliptic, and the orbits of the planets are nearly circular • The Sun has a relatively slow rotation [What happened to Pluto?]
Inner planets are made of rocks and metals – Terrestrial Planets Outer planets are made of gases and ices – Gas Giants Our solar system also includes about 138 satellites (like our moon), numerous asteroids, as well as comets and meteors (“shooting stars” and meteorites) [Does our moon have any impact on our environment?]
2. THE SUN AND SOLAR RADIATION The Sun and Its Energy • The sun is a self-luminous sphere of gasses that emit radiant energy. • It is like a giant thermonuclear furnace with fusion reactions, and a core temperatures exceeding 27,000,000˚ F • At its luminous outer surface, the Photosphere, temperatures fall to 10 -11,000˚F – then the Chromosphere, and then the Corona • Charged particles (protons & electrons) from the corona flow along the sun’s magnetic field lines into space as Solar Wind – interacts with ions in earth’s outer atmosphere to produce the colorful light shows, the Auroras (Aurora Borealis and Aurora Australis) • Sunspots, caused by magnetic storms on the sun, are dark regions on the photosphere, 15000 C - 20000 C cooler than the surrounding, and they signify increased solar activity, peaking in 11- year cycles – the next peak is estimated to be in 2012 • (Remember the recent movie, “2012” ?)
Solar Flares (as well as other prominences and coronal mass ejections) occur in the region of sunspots, sending out energized, charged particles at great speeds toward the earth. . .
Insolation and Atmospheric Dynamics • Incoming solar radiation, or insolation, is the major source of energy both directly and indirectly for the entire solar system • The rate of a planet’s receipt of solar energy is called the solar constant • Energy is emitted by the sun in the form of electromagnetic energy, travelling in a spectrum of varying wavelengths, takingabout • 8.3 minutes to reach earth • This radiant energy is largely shortwave radiation, composed of Ultraviolet rays, X-rays and Gamma rays (9%); visible light (41%); various infrared wavelengths (49%); and microwave, television and radio wavelengths (1%) • Earth receives only 1/2,000,000,000 (one two billionth) of the sun’s radiation, but that’s what drives much of the atmospheric, physical and biological processes of the earth system
Spatial and Seasonal Variations in Insolation • over the surface of the earth depends largely on 3 factors: • Duration of daylight (varies by latitudes and seasons); • 12-hour days year-round at the equator, greater variability • toward the poles, with the poles experiencing essentially • one long 6-month long day, and a similarly long night • Angle of solar rays (which affects intensity); and • Caused by earth’s inclination, rotation, revolution • Earth’s atmosphere (some radiation is absorbed by clouds, some reflected back). • Unlike solar radiation, earth radiation is longwave • The first two factors above relate to the third aspect of Earth-Sun Relationships – Inclination and Movements of Earth – and their Implications
3. INCLINATION AND MOVEMENTS OF EARTH: • Day-Night, Length of Day, Seasons, Latitudinal Zones • Five Important Factors or Determinants: • SPHERICITY • ROTATION • AXIAL TILT – INCLINATION • AXIAL PARALLELISM • REVOLUTION 1. SPHERICITY Earth appears as an oblate spheroid to the Sun’s parallel rays; the geoid Effects of Earth’s Sphericity
2. ROTATION • The Earth rotates on its axis • One complete rotation (3600) takes • approximately 24 hours • Rotation is from West to East • Sun appears to ‘rise’ in East and ‘set’ in West
3. AXIAL TILT – INCLINATION and Plane of Ecliptic Earth’s axis is tilted about 23.5˚ from perpendicular to Plane of Ecliptic; 4. PARALLELISM Earth’s axis remains in a fixed alignment with Polaris directly overhead, throughout the year, as it revolves about the Sun
5. REVOLUTION • The Earth revolves around the Sun in one year (365.25636 days) • The Earth’s revolution is slightly elliptical, not circular – • Direction of revolution is counter-clockwise • Earth moves in a constant plane – Plane of the Ecliptic – in its revolution about the Sun – Earth’s Orbit The Orbit of the earth is an elliptical path along the Plane of Ecliptic Average orbital length = 940,416,480 km Closest approach to the Sun = 147 million km, Perihelion (January 3) Farthest distance from the Sun = 152 million km, Aphelion (July 4)
Implications and Effects: • Alternating Day and Night • – Circle of Illumination • Length of Day • – Variations due to: • Inclination of earth’s axis • Plane of Ecliptic, and Parallelism • Earth’s revolution around the sun, • which results in: • 2 Solstices (Summer, Winter) • 2 Equinoxes (Vernal, Autumnal) • [See: Figure 3.17 in Text, • and Read the Explanation ]
In the Northern Hemisphere, A: Summer Solstice* B: Autumnal Equinox C: Winter Solstice* D: Vernal Equinox *During the 2 Solstices, the situations are reversed in the Southern Hemisphere
Percentage of Insolation striking various latitudes during an equinox The Sun’s Rays in Summer (b) and Winter (c)
GALACTIC MOVEMENT: • Earth’s axis wobbles through (22˚-24.5˚) time and will not always maintain a constant angle • Earth’s orbit around the sun will also change from more circular to more elliptical (Milankovitch Cycles) • [Explains Cycle of Ice Ages?] • Why? • Effects of • Galactic Motion?