GK (Solar System)

The average distance from Earth to the Moon is approximately 384,400 kilometers. This is a well-established astronomical measurement based on the Moon's elliptical orbit around Earth, varying slightly at perigee and apogee.

The Apollo 11 mission landed on the Moon on July 20, 1969 (UTC time), which was July 21, 1969 in some time zones including parts of the US. Neil Armstrong and Buzz Aldrin became the first humans to walk on the lunar surface.

A lunar eclipse occurs when Earth passes directly between the Sun and Moon, casting Earth's shadow on the Moon's surface. This celestial event can only happen during a full moon when the Sun, Earth, and Moon are aligned.

The Moon is Earth's only natural satellite. While Earth has thousands of artificial satellites (spacecraft, debris), the Moon is the sole natural body that permanently orbits our planet.

Mars is called the "Red Planet" because its surface appears reddish due to iron oxide (rust) prevalent in the soil and rock. This distinctive reddish-orange appearance has been observed since ancient times and makes Mars easily identifiable.

Venus is the only planet in our solar system that rotates backwards (retrograde rotation), meaning it spins in the opposite direction to most other planets. This unique rotation is thought to have been caused by a massive collision early in its history. Mars, Earth, and Saturn all have prograde rotation like most planets.

William Huggins, a pioneering astronomer, discovered water vapor in Mars' atmosphere in 1867 using spectroscopy. This was one of the first major discoveries using spectroscopic techniques in planetary astronomy. The other names listed are not associated with this discovery.

Titan, Saturn's largest moon, is the only satellite in our solar system proven to have a substantial atmosphere - primarily nitrogen with methane and other hydrocarbons. Its thick atmosphere is even denser than Earth's. No other moons have been confirmed to have significant atmospheres.

Venus is the brightest planet in Earth's sky due to its proximity and highly reflective cloud cover. It can shine at magnitude -4.6, making it visible even during daytime. Uranus, Pluto, and Mars are much dimmer and not as easily visible.

The Moon's mass is approximately 1/6th that of Earth, which is why astronauts weigh much less on the lunar surface. This ratio also explains why the Moon's gravity is about 16.6% of Earth's. The other fractions (1/4, 1/5, 1/8) are incorrect.

Jupiter is the largest planet in our solar system, with a mass more than twice that of all other planets combined and a diameter over 11 times Earth's. Saturn, while also a gas giant, is significantly smaller than Jupiter. Uranus and Earth are much smaller.

Johannes Kepler provided mathematical proof of the Copernican heliocentric model through his three laws of planetary motion. His laws showed that planets move in elliptical orbits around the Sun, not perfect circles as Copernicus originally proposed. The other names are not associated with this proof.

Ganymede, Jupiter's largest moon, is the largest satellite in our solar system - even bigger than the planet Mercury. It's one of the Galilean moons discovered by Galileo. Titan is the second-largest moon. The other options are fictional names.

Venus is the hottest planet due to its thick CO2 atmosphere creating an extreme greenhouse effect, with surface temperatures around 465°C. Though Mercury is closer to the Sun, Venus traps heat more effectively. Earth, Mars, and Uranus are much cooler.

Mercury is the lightest planet in our solar system, with a mass of only about 0.055 Earth masses. It's the smallest planet and the closest to the Sun. Mars, Jupiter, and Earth are all significantly more massive.

Jupiter is the most massive (heaviest) planet in our solar system, with a mass of about 318 Earth masses. Its enormous gravity and size make it the undisputed heavyweight. Mars and Earth are terrestrial planets with much less mass, while Pluto is a dwarf planet.

Mercury is the innermost planet in our solar system, orbiting at an average distance of about 58 million km from the sun. Its proximity to the sun gives it the shortest orbital period (88 days) and extreme temperature variations.

Neptune was discovered in 1846 through mathematical predictions. Urbain Le Verrier (France) and John Couch Adams (England) independently calculated the position of an unknown planet causing orbital irregularities in Uranus, leading to its discovery.

Galileo Galilei was the first to observe celestial satellites through a telescope in 1610 when he discovered Jupiter's four largest moons (now called the Galilean moons: Io, Europa, Ganymede, and Callisto). This revolutionized astronomy and supported the heliocentric model.

Mercury has the shortest orbital period of all planets at approximately 88 Earth days. This is because it's closest to the sun and therefore experiences the strongest gravitational pull, requiring it to move faster to maintain its orbit.