Autumn is one of the seasons in which the leaves of trees and plants turn pale. It is the transition between the summer and the winter seasons. In this season, the temperature gradually falls down and trees are seen shedding their leaves and flowers.

Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans, aquifers and groundwater). Harmful substances such as sewage, toxic chemicals, silt, etc. gets mixed with water, thereby polluting it.

During the day time, land gets heated faster than water. The hot air above land is replaced with cold air from sea. This phenomenon is known as sea breeze.

Increase in amount of carbon dioxide in air results in global warming and greenhouse effect.

Most of the radiations that Earth receives by the Sun is reflected back. Earth gets heated up by these reflected radiations and this heat is trapped by the atmosphere. This phenomenon is called green house effect and due to this heating there is an increase in the average temperature of the Earth's atmosphere. This is called global warming.

Greenhouse gases are the gases in the atmosphere that are capable of absorbing the infrared radiations from the earth, thereby trapping the heat in the atmosphere. This trapped heat is increasing the global temperature leading to global warming and this phenomenon is known as the greenhouse effect. Examples of greenhouse gases are methane, water vapour, carbon dioxide.

When the Earth rotates, half of the Earth will be exposed to the rays of the sun while the other half remains dark. It is daytime on the side facing the sun while its night time on the other side of the Earth. So, the Earth's rotation results in day and night.

.

The celestial bodies in the universe which generate light of their own are called stars.
Sun is the closest star to the Earth. It is made up of gases like hydrogen and helium. It is the primary source of light and energy of our solar system.

The Earth revolves in its orbits around the Sun. It takes approximately 365.5 days to complete one revolution around the Sun.