Motion in the Universe

MOTION OF OBJECTS IN THE SOLAR SYSTEM

Planets: Planets orbit the sun in elliptical paths known as orbits. This movement is governed by the gravitational pull of the sun.
Moons: Moons orbit the planets to which they are gravitationally bound. The time it takes for a moon to complete one orbit is called its orbital period.
Comets: They follow highly elliptical orbits around the sun. As they approach the sun, increased heat causes gas and dust to be released from the comet, forming a tail that always points away from the sun due to the solar wind.

ROTATION OF CELESTIAL BODIES

Earth’s Rotation: Earth rotates on its own axis once every 24 hours, causing day and night cycles. The direction of rotation is from west to east which results in the apparent movement of the sun and stars from east to west.
Other Planets: Planets also rotate on their own axis, but the duration and direction of rotation can vary. For instance, Venus rotates in the opposite direction to most other planets.
Stars: Stars rotate around their own axis. The speed of rotation can affect the star’s shape and its observed properties.

RED SHIFT IN THE UNIVERSE

Cosmological Red Shift: Observations of distant galaxies indicate that their light is shifted towards the red end of the spectrum. This is known as red shift and signals that the galaxies are moving away from us.
Expanding Universe: The observation of red shift in the light from distant galaxies is the key evidence for the Big Bang theory. The detection of red shift from all directions suggests that the universe is expanding uniformly.
Hubble’s Law: The astronomer Edwin Hubble discovered a direct relationship between the red shift of a galaxy and its distance from us. This relationship, known as Hubble’s Law, forms the basis of measurements of cosmic distances.

GRAVITATIONAL FORCES IN THE UNIVERSE

Gravity: Every object in the Universe exerts a gravitational force on every other object. The force is dependent on the masses of the objects and the distance between them.
Orbital Motion: Gravitational forces are responsible for the orbital motion of planets around stars and moons around planets. Newton’s laws of motion and gravitation can be used to describe and predict this motion.
Tides: The gravitational pull of the Moon and the Sun causes high and low tides on Earth. The gravitational force from the Moon is stronger, hence high tides align with the Moon’s position.

Mastery over these principles of motion in the universe is a crucial component of your astrophysics revision. Always ensure understanding of concepts, laws, and their application in different contexts.