An inferior planet is one that is a. smaller than Earth. b. larger than Earth. c. closer to the Sun than Earth is d. farther from the Sun than Earth is.

Planets in our Solar System follow elliptical paths around the Sun, known as orbits. The position of a planet's orbit plays a crucial role in different terminologies used in astronomy. For instance, the terms 'inferior planet' and 'superior planet' are determined based on a planet's orbit relative to Earth's orbit.

An 'inferior planet' refers to a planet whose orbit lies within Earth's orbit. Simply put, these planets are closer to the Sun than Earth. On the other hand, 'superior planets' have orbits that lie outside Earth's orbit, meaning they are farther from the Sun than Earth.

This distinction helps astronomers understand and predict the movement and visibility of different planets in the sky. Inferior planets can achieve positions called 'inferior conjunction' when they are between Earth and the Sun, and 'superior conjunction' when they are on the opposite side of the Sun from Earth.

Mercury is the closest planet to the Sun and one of the two inferior planets in our Solar System. It has a very short orbit around the Sun, taking about 88 Earth days to complete one revolution. Due to its proximity to the Sun, Mercury experiences extreme temperatures, ranging from very hot to extremely cold.

Unique Points about Mercury:

• Mercury does not have a significant atmosphere, which means it cannot retain heat.
• It has a rocky surface with many craters, similar to our Moon.
• Despite being one of the smallest planets, Mercury has a large iron core, making up a significant portion of its mass.

Observing Mercury from Earth can be tricky because it is often lost in the Sun's glare. The best times to observe Mercury are during its greatest elongations, the points in its orbit where it is farthest from the Sun in the sky.

Venus is the other inferior planet in our Solar System, orbiting the Sun at about 225 Earth days. It is often called Earth's 'sister planet' due to its similar size and composition. However, Venus has many unique features that distinguish it from Earth.

Key Characteristics of Venus:

• Venus has a thick, toxic atmosphere composed mainly of carbon dioxide, with clouds of sulfuric acid.
• The atmosphere creates a severe greenhouse effect, making Venus the hottest planet in our Solar System.
• Venus rotates on its axis in the opposite direction to most planets, including Earth. This means the Sun rises in the west and sets in the east on Venus.

Venus is second only to the Sun and Moon in terms of brightness in our sky, often seen during dawn or dusk and known as the 'Morning Star' or 'Evening Star.' Observing Venus helps us understand climate dynamics and atmospheric properties, which are vastly different from those of Earth.