### Theory:

Inner or Terrestrial Planets:
 Mercury Venus Smallest and closest planet to the Sun Second planet from the Sun Airless and waterlessplanet. Earth’s Twin (almost the same size as the Earth) No atmosphere No atmosphere Experiences extremes of temperature Longest rotation period ($$243$$ days) No satellites No satellites Mercury can be viewed in the morning and evening with naked eye. Visible in the mornings and the evenings. Also called as the Morning Star and the Evening Star. Rotates from West to East. It rotates in the opposite direction to all other planets except Uranus, i.e. East to West. After the Moon, it is the brightest natural object in the night sky. Named after the Roman deity ‘Mercury’, the Messenger to the Gods. Named after the Roman Goddess of love and beauty.

• Mercury is only about as wide as the Atlantic Ocean.
• Venus has yellowish clouds made of sulphur and sulphuric acid cover the entire planet causing light to reflect off the surface.
Inner or Terrestrial Planets:
 Earth Mars Third Planet from Sun and fifth largest planet. Fourth planet from the Sun and second smallest planet in the solar system. Only planet known to support life. It also has polar ice. Atmosphere mainly made of: Nitrogen ($$78$$%) and Oxygen ($$21$$%) Thin atmosphere Rotation period: $$23$$hours, $$56$$minutes Satellite: Moon Satellites: Phobos and Deimos Also known as Blue planet’ or ‘Watery planet’ because three-fourth of the Earth is covered by water. Appears red, due to the presence ofiron oxide on its surfaceOften described as The Red Planet. Rotates from West to East Rotates from West to East The only planet in the solar system which is not named after any Greek or Roman deity. Named after the Roman God of war.

Polar diameter: $$12,714$$  km
Equatorial diameter: $$12,756$$  km
The Earth revolves around the Sun at a speed of about $$30$$  kmper second.
The distance between the Sun and the Earth is about $$150$$ million kilometres (or $$1$$$$Astronomical$$$$Unit$$).