[Physics Class Notes] on Planets Pdf for Exam

The word planet is derived from the word “planets” which means wanderer this name is given to them as they appear to wander in the night sky from east to west while stars also move from east to west but they seem to remain fixed relative to each other and the planet relative to them seem to move forward and backward. 

 

A planet is a celestial body that revolves around the sun in fixed orbits and planets do not have the light of their own but reflects the light of the sun they also do not twinkle like other stars as they are too close to us and till now the earth is the only known planet to harbor life and have the favorable condition.

 

Understanding the Planets

According to the widely accepted Big Bang theory, our Universe started with an explosion of a concentrated mass in space. Later the constellation of stars and planet systems emerged.

 

Our solar system is one of such many planetary systems. It consists of 8 planets in the order of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was discarded from the list in August 2006 by the International Astronomical Union (IAU). It is now recognized as a dwarf planet.

 

The Sun present at the center of the Solar system is the hinge point and source of energy for all planets.  The first four inner planets are termed terrestrial planets as they are constructed of solid mass and have hard surfaces. They are also known as telluric planets or Rocky planets. The four exterior planets are giant balls of gases and are termed Jovian planets. 

 

Mankind has had knowledge about planets since ancient ages but after the invention of telescopes, scientists discovered the presence of the lesser-known Uranus, Neptune, and Pluto.

 

Earth is the most distinct planet of all because of the life system it sustains. Being located at a very appropriate distance from the sun which maintains a convenient environment that is neither too hot nor too cold makes it possible.

 

Notes on Planets

Mercury 

It’s the nearest planet to the sun and is also the smallest planet in the solar system and takes around 88 days to complete one revolution (to be exact 88.97 days) which is the smallest time duration.

 

Its size is slightly larger than the size of the moon of earth. It does not have many moons and climatic conditions that are not favorable for any form of life as it is too near to the Sun. Its surface temperature ranges from 100 K at night to 700 K during the day (this high diurnal range of temperature is there because the planet has no atmosphere to retain and this is the highest among all planets).

 

It’s the second densest planet in our solar system with the smallest tilt in its axis among all the planets in the solar system.

 

Venus

When observed from the Earth, it’s the second brightest (after the observed moon) and takes 224.7 Earth days to complete one revolution and 243 Earth days for rotation on its axis (it takes the maximum time period among all planets to complete one rotation). It rotates in the opposite direction to all planets except Uranus (from West to East).

 

It’s also observed that one day on Venus is equal to one year on Earth. It’s also called Earth’s twin sister because of its similar size, shape, mass, and proximity to the sun and of its bulky composition. It’s not suitable for human settlement because it contains 96% carbon in the atmosphere. The surface temperature is very high (a mean temperature of 735K), making it the warmest planet in our solar system.

 

Earth

It’s the third planet from the Sun and is the only known planet to harbour life. The Earth’s age is around 4.5 billion years old. It takes 365.264 days to complete one revolution around the Sun and 24 hours to complete one rotation on its axis (and after every four complete revolutions [4 years] it takes a day longer 366 days to complete a revolution). It is covered by 71% of water and its crust is divided into different tectonic plates (lithosphere). Earth’s innermost part remains active and its inner core is solid while the outer core is liquid which generates Earth’s magnetic field.

Mars

It’s the fourth planet from the sun and also the second-smallest in the solar system. Its red colour also makes it known as the red planet (presence of iron oxide). It has two moons – Phobos and Deimos. Its gravity is 38% of the Earth’s gravity and takes 687 Earth’s day and one full Mars year (16,500 hours).

Jupiter

It’s the fifth planet from the Sun and the largest planet among all. It’s also one of the brightest things that can be seen in the sky with the naked eye.

 

Jupiter is a giant ball of gases with a one-thousand mass of the Sun and lacks a well-defined surface. 
 

Saturn

It’s the sixth planet from the Sun and the second-largest planet in the solar system. It’s a giant gas planet with an average radius that is nine times the radius of the earth. The inner core is made of iron and nickel. An electric current within the hydrogen layer gives rise to the magnetic field of Saturn which is a little less than the earth’s magnetic field.
 

Uranus

It’s the seventh planet from the Sun and has the fourth-largest planet by mass and third-largest by radius. It’s also referred to as ice giant and its primary component is similar to Jupiter and Saturn but it also has more ices such as methane, water, and ammonia and also traces of hydrocarbons. It rotates in the opposite direction from all the planets except venus( it rotates from west to east).
 

Neptune

It’s the eighth planet from the Sun. It’s the fourth-largest planet by diameter. The third most massive planet and is the densest giant planet – it’s slightly larger than Uranus and Neptune. It orbits the Sun every 164.8 years and is denser than Uranus and physically smaller than Uranus.

 

By the recent developments in more powerful telescopes and assisted by space exploration we have come to know about the presence of similar kinds of planets in other systems and constellations. With the unending effort of our Scientists and Astronomers, we may be surprised by the revelation of many mysteries that our Universe holds.