Cosmos Fundamentals: Universe Origins and Earth’s Movements
Origin of the Universe: The Big Bang Theory
Postulated by George Gamow in 1949, the Big Bang Theory describes the universe’s beginning as a massive explosion. This explosion resulted from the universe’s high density and temperature, exceeding a billion degrees Celsius, which led to the formation of the atom’s basic structure.
Theory of the Expanding Universe
The first four minutes after the Big Bang, termed “zero minutes,” saw a temperature drop leading to the union of atoms. Over the next 700,000 years, the temperature continued to fall, producing more complex chemical links. These allowed the formation of solid matter. The combustion of hydrogen, converting it into helium, created distinct links in the universe, releasing energy as radiation. This caused a gradual temperature loss due to the expansion of gases like hydrogen, forming stars. The distances between galaxies are greater now than in the past. In the 1960s, scientists discovered that celestial bodies still retain residual energy from the Big Bang.
Milky Way Galaxy
The Milky Way is a spiral galaxy with four arms: Crux-Centaurus, Perseus, Sagittarius, and Orion. It houses our solar system and was discovered by Democritus. In 1609, Galileo Galilei used his telescope to prove that this bright spot was composed of thousands of stars. It measures about 100,000 light years and contains over 200 billion stars. The Sun is 25,000 light years from the center. The brightest star is Alpha Centauri, a close binary or double star.
Constellations
Constellations are groupings of stars, with 88 recognized today. Ancient civilizations used them for guidance, creating imaginary lines and names referring to objects, figures, characters, or animals. During the year, Earth orbits the Sun along the zodiac, which contains twelve constellations.
Celestial Sphere
Viewing Earth from space, it appears as a vault called the celestial sphere containing the stars. The highest point of the celestial sphere is the zenith. The opposite point is the nadir. The horizon divides the sphere into the upper (visible) and lower (invisible) hemispheres. The celestial sphere has two celestial poles, projections of Earth’s geographic poles.
Norths
- Astronomical North: Located at Polaris (the Pole Star).
- True North: Where Polaris is projected onto Earth’s surface.
- Magnetic North: Affected by Earth’s magnetic field, located near Bathurst Island in Canada.
Cardinal Points
The directional system used by humans consists of four points: North, South, East, and West.
Ecliptic and Earth’s Axial Tilt
The ecliptic plane is the imaginary plane perpendicular to Earth’s orbital axis around the Sun. Eclipses occur when the Moon, Sun, and Earth intersect on this plane. Earth’s axis is the central axis perpendicular to the equatorial plane, defining the geographic North and South poles. The equator is inclined 23° 27′ to the ecliptic, making Earth’s axis tilted 66° 33′ relative to the ecliptic.
Shape of the Earth
While a sphere is the closest geometric approximation, Earth’s actual shape is an ellipsoid. However, this doesn’t account for surface features like mountains and ocean basins. Geodesy, the science of Earth’s shape and dimensions, uses the geoid, a physical model representing the planet’s actual shape, considering a constant gravity potential at mean sea level.
Earth’s Motions
- Rotation: Earth spins on its axis from west to east, defining the passage of time. A mean solar day averages 24 hours.
- Revolution: Earth orbits the Sun, completing one orbit in a year. The orbit is elliptical, with the Sun at one focus. Perihelion is the closest point to the Sun, and aphelion is the farthest.
- Precession: The Sun’s gravitational pull causes a slow shift in Earth’s axial tilt, completing a cycle in about 26,000 years (a Platonic year).
- Nutation: A slight wobble in Earth’s axial tilt, caused by the Moon’s gravitational influence.
Consequences of Rotation
The primary consequence is the cycle of day and night.
Consequences of Revolution
The main consequences are the seasons, resulting from Earth’s axial tilt and its orbit around the Sun, leading to solstices and equinoxes.