Astronomy and Cosmology

Sirius, also known as the Dog Star (Alpha Canis Majoris), is the brightest star in the night sky with an apparent magnitude of -1.46. It is approximately 8.6 light-years from Earth. Vega, Alpha Centauri A (actually a three-star system with Alpha Centauri A being similar to our Sun), and Capella are all bright but significantly dimmer than Sirius.

Lenticular galaxies are disk galaxies that have lost their spiral structure and appear lens-shaped. They have a central bulge and disk but no spiral arms, distinguishing them from both spiral and elliptical galaxies. The name literally means 'lens-shaped'.

The Hubble Space Telescope is the primary instrument used to observe and track movements of galaxies. Note option C has the correct spelling while option B does not.

The Sombrero Galaxy (M104) gets its name from its distinctive hat-like appearance when viewed from Earth, with a bright nucleus surrounded by a thick dust lane that resembles a Mexican sombrero's brim. It is located in the Virgo constellation, about 29 million light-years away.

The Large Magellanic Cloud (LMC) is named after the Portuguese explorer Ferdinand Magellan, whose crew documented these satellite galaxies during their circumnavigation voyage in the 16th century. The LMC is the largest satellite galaxy of the Milky Way.

Cygnus A was one of the first radio galaxies discovered (in the 1940s) and is one of the brightest radio sources in the sky. It is a powerful radio galaxy located in the Cygnus constellation, approximately 600 million light-years from Earth, and its discovery helped establish radio astronomy.

The Cigar Galaxy (Messier 82 or NGC 3034) is a starburst galaxy in the constellation Ursa Major that gets its name from its elongated, cylindrical shape resembling a cigar. It is located approximately 12 million light-years from Earth and is undergoing intense star formation activity.

The Canis Major Dwarf Galaxy is the closest known galaxy to the Milky Way, located approximately 25,000 light-years from our solar system. It was discovered in 2003 and is classified as a dwarf galaxy. Many people mistakenly think Andromeda is nearest, but Andromeda is about 2.5 million light-years away.

The Baby Boom Galaxy (M82) is recognized as the brightest galaxy in the infrared spectrum due to its intense star formation activity. It earns its name from the exceptionally high rate of star birth, producing stars at a rate hundreds of times faster than our Milky Way. Note that option B has a typo - it should be 'Andromeda'.

Messier 87 (M87), also known as Virgo A, is one of the most massive galaxies in the local universe, containing several trillion stars. It's a giant elliptical galaxy famous for hosting the first black hole ever directly imaged. While Andromeda is larger than the Milky Way, M87 is significantly more massive than both, with an estimated mass of about 2.4 trillion solar masses.

In stellar astronomy, blue dwarfs are young, hot stars that burn brightly with blue-white light, while red giants are older stars in a late stage of stellar evolution that have expanded and cooled, appearing red. The color indicates the star's temperature and evolutionary stage.

Sidereal time is measured relative to distant stars (fixed points far beyond our solar system). A sidereal day is about 23 hours 56 minutes and 4 seconds - Earth's actual rotation period. An ephemeris is a table of celestial positions. Caesium is used in atomic clocks. 'Timilithic' appears to be a made-up word.

The largest known galaxies can contain up to approximately 400 billion stars. Giant elliptical galaxies like M87 and IC 1101 are examples of such massive stellar systems. Smaller galaxies may have 100-300 billion stars, making 400 billion the upper limit among known galaxies.