astronomy

Yuri Gagarin's spaceflight on April 12, 1961, lasted 108 minutes and orbited Earth once.

The Mir space station, operated by the Soviet Union and Russia, was inhabited from 1986 to 2001.

Apollo 17, in December 1972, was the last crewed mission to land on the Moon.

Apollo 13 launched April 11, 1970, and returned safely to Earth despite an in-flight oxygen tank explosion.

The Fermi paradox is the apparent contradiction between high estimates of the probability of extraterrestrial civilizations and the lack of evidence for them.

Pulsars are rapidly rotating neutron stars that emit beams of electromagnetic radiation observable as regular pulses.

Edwin Hubble's earlier 1924 discovery established that the Andromeda nebula was a separate galaxy beyond the Milky Way.

Johannes Kepler's three laws of planetary motion describe orbits as ellipses with the Sun at one focus, equal areas in equal times, and a relationship between period and orbital semi-major axis.

The Solar System has eight recognized planets following Pluto's reclassification in 2006.

Voyager 2, launched in 1977, is the only spacecraft to have visited Uranus (1986) and Neptune (1989).

The Galileo spacecraft orbited Jupiter from 1995 to 2003 and provided extensive data on the planet and its moons.

Valentina Tereshkova orbited Earth 48 times during her 1963 mission aboard Vostok 6.

The first artificial satellite, Sputnik 1, orbited Earth from October 1957 to early January 1958 before reentering the atmosphere.

The Space Shuttle program operated from 1981 to 2011 and conducted 135 missions.

The Vostok program of the Soviet Union conducted the first six crewed orbital spaceflights from 1961 to 1963.

The Drake equation estimates the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

Quasars are extremely luminous active galactic nuclei powered by accretion onto supermassive black holes.

White dwarfs are dense stellar remnants formed when stars of less than about 8 solar masses exhaust their nuclear fuel.

Cepheid variable stars have a known relationship between their luminosity and pulsation period, making them valuable as distance indicators.

Edwin Hubble showed in 1929 that distant galaxies are moving away from us, with their recession velocity proportional to distance.

Tycho Brahe made highly accurate astronomical observations in the late 16th century, providing data that Kepler used to formulate his laws.

Light from the Sun takes approximately 8 minutes and 20 seconds to reach Earth.

Jupiter is the largest planet in the Solar System with a mass about 318 times that of Earth.

The observable universe is approximately 93 billion light-years in diameter.

Pluto was reclassified from a planet to a dwarf planet by the IAU in August 2006.

Venus has the longest rotation period of any planet in the Solar System, lasting about 243 Earth days.

Neptune is the windiest planet, with measured winds exceeding 2,000 kilometers per hour.

The Sun's photospheric temperature is approximately 5,778 Kelvin.

The Milky Way galaxy contains an estimated 100 to 400 billion stars.

A light-year is the distance light travels in one Julian year, approximately 9.46 trillion kilometers.

The first exoplanet orbiting a Sun-like star, 51 Pegasi b, was discovered in 1995 by Mayor and Queloz.

The Chicxulub impactor that contributed to the extinction of non-avian dinosaurs struck Earth approximately 66 million years ago.

Sagittarius A*, the supermassive black hole at the center of the Milky Way, has a mass of about 4.3 million solar masses.

The Sun is approximately 4.6 billion years old.

The Big Bang occurred approximately 13.8 billion years ago, based on Planck satellite measurements.

Dark matter is inferred to make up about 27 percent of the universe's mass-energy content.

The Hertzsprung-Russell diagram plots stars by luminosity against effective temperature.

A solar eclipse occurs when the Moon passes between the Sun and Earth, partially or fully blocking the Sun.

Carl Sagan was an American astronomer and science communicator best known for the Cosmos television series.

One astronomical unit (the average Earth-Sun distance) is defined as exactly 149,597,870,700 meters.

The cosmic microwave background has a near-uniform temperature of approximately 2.725 Kelvin.

Proxima Centauri is the closest known star to the Sun at approximately 4.24 light-years away.

Earth's axial tilt is approximately 23.44 degrees relative to its orbital plane.

The Moon is gradually receding from Earth at about 3.8 centimeters per year.

Mercury is the smallest planet in the Solar System and the closest to the Sun.

Mars has two small moons named Phobos and Deimos.

Saturn's most prominent rings are composed primarily of water ice particles.

Uranus rotates on its side, with an axial tilt of about 98 degrees.

The Sun accounts for approximately 99.86 percent of the total mass of the Solar System.

Andromeda is the nearest large spiral galaxy to the Milky Way, at approximately 2.5 million light-years away.

Halley's Comet has an orbital period of approximately 76 years and last appeared in 1986.

The Hubble Space Telescope was launched into low Earth orbit on April 24, 1990.

The James Webb Space Telescope was launched on December 25, 2021.

Voyager 1, launched in 1977, became the first human-made object to enter interstellar space in August 2012.

A neutron star can have a mass roughly 1.4 to 2.3 times that of the Sun packed into a sphere about 20 kilometers across.

The first image of a black hole, Messier 87*, was released by the Event Horizon Telescope collaboration on April 10, 2019.

Mars has the largest known volcano in the Solar System, Olympus Mons, rising about 21.9 kilometers above its surrounding plains.

Earth is approximately 4.54 billion years old, based on radiometric dating of meteorites.

Dark energy accounts for approximately 68 percent of the universe's total mass-energy content.

Nicolaus Copernicus formulated the heliocentric model of the Solar System, published in 1543.

The International Space Station has been continuously occupied by humans since November 2, 2000.

The Mars rover Perseverance landed in Jezero Crater on February 18, 2021.

Curiosity, a Mars rover the size of a small car, has been exploring Gale Crater since August 2012.

The Cassini-Huygens mission orbited Saturn from 2004 to 2017 and deployed the Huygens probe to Titan in January 2005.

Pioneer 10, launched in 1972, was the first spacecraft to traverse the asteroid belt and to make direct observations of Jupiter.

New Horizons performed a flyby of Pluto on July 14, 2015, providing the first close-up images of the dwarf planet.

Comets are icy bodies that develop visible comae and tails when they approach the Sun.

Asteroids are rocky remnants from the formation of the Solar System, with most located in the asteroid belt between Mars and Jupiter.

Meteors are streaks of light caused by small meteoroids burning up as they enter Earth's atmosphere.

The Kuiper Belt is a region of the Solar System beyond Neptune containing many small icy bodies, including Pluto.

The Oort Cloud is a hypothetical spherical cloud of icy bodies surrounding the Solar System at great distances and is thought to be the source of long-period comets.

Galileo Galilei discovered the four largest moons of Jupiter, now known as the Galilean moons, in 1610.

Saturn has at least 146 confirmed moons, the most of any planet in the Solar System.

The Crab Nebula is a supernova remnant from a stellar explosion observed in 1054 CE.