Astronomy : Stars & Satellites (Moons)

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Some Important Stars

The nearest star to the Earth is the Sun, which is at a distance of 92,955,900 miles from the Earth. The distance of the Sun from the Earth is termed as 1 Astronomical Unit. Light from the Sun takes nearly 8 minutes to reach the Earth.

The nearest star to the Earth (other than the Sun) is Proxima Centauri, which was discovered in the year 1915. It is at a distance of nearly 4.2 light years from Earth. One light year is equal to the distance light travels in one year.

The largest star is Betelgeuse (Alpha Orionis).

The brightest star visible from the surface of the Earth is Sirius A (Alpha Canis Majoris), also known as the Dog Star. It has an apparent brightness magnitude of −1.46. It is nearly 8.65 light years away from the Earth and has a luminosity 26 times greater than that of the Sun. It is visible in the winter months of the northern hemisphere.

Some Important Natural Satellites (Moons)

The largest natural satellite of our solar system is Ganymede, one of Jupiter's 16 moons, with a diameter of 3270 miles (5262 km). Ganymede is also the heaviest natural satellite of our solar system with a mass nearly double that of our Moon.

The second largest natural satellite of our solar system is Titan, one of Saturn's moons, with an equatorial diameter of 3200 miles (5150 km).

The natural satellite that is closest to the parent planet is Phobos. It is one of the 2 satellites of Mars (the other is Deimos). It is at a distance of nearly 5800 miles from the center of Mars.

The natural satellite that is farthest from the parent planet is Sinope. It is the outermost of the 16 natural satellites of Jupiter and is at a staggering distance of 14 million miles from Jupiter.

The most distant natural satellite of our solar system is Charon, which is the only known moon of Pluto.

Natural Satellites (Moons) of Planets

A natural satellite revolving around a planet is called a moon. Note that moons are being continuously discovered in the outer solar system by astronomers with the aid of powerful telescopes and equipment. Thus, the number of moons for the Jovian planets (namely, Jupiter, Saturn, Uranus and Neptune) is not known with certainty.

The planets, Mercury and Venus, have no natural satellites (moons).

The Moon is Earth's only natural satellite. Although its diameter is about one-fourth that of the Earth, it appears large because it is our closest celestial neighbor. It revolves around the Earth at a distance of about 238600 miles (384000 km).

The two natural satellites (moons) of Mars are Phobos (about 7 miles or 11 km in diameter) and Deimos (about 4 miles or 6 km in diameter). They were discovered by Asaph Hall in 1877.

The four largest of the (16 or more) natural satellites (moons) of Jupiter are Io, Europa, Ganymede and Callisto. They are known as Galilean satellites because they were discovered by Galileo in 1610, soon after he invented the telescope.

The largest of the (18 or more) natural satellites (moons) orbiting Saturn is Titan. Titan was discovered by Dutch astronomer, Christiaan Huygens, and is the prime target of the Cassini-Huygens mission.

The largest of the (15 or more) natural satellites (moons) of Uranus is Titania.
Many of Uranus' natural satellites (moons) are named after Shakespearian characters as listed below :
Cordelia (from King Lear), Ophelia (from Hamlet), Bianca (from Othello and The Taming of the Shrew), Cressida (from Troilus and Cressida), Desdemona (from Othello), Juliet (from Romeo and Juliet), Portia (from The Merchant of Venice), Rosalind (from As You Like It), Belinda (from The Rape of the Lock by Alexander Pope), Puck (from A Midsummer Night's Dream), Miranda (from The Tempest), Ariel (also from The Tempest), Titania (from A Midsummer Night's Dream), and Oberon (also from A Midsummer Night's Dream).

The largest of the (8 or more) natural satellites (moons) of Neptune is Triton. Voyager 2 is the only spacecraft to pass Triton.

The only known moon orbiting Pluto is Charon. Charon and Pluto are 'tidally locked', which implies that the same side of Charon always faces Pluto and vice versa.