Astronomy for GCSE






Astronomy... 2. Fundamentals

Here are some interesting points from the first chapter:
  • If we scale things down so the sun is only an inch away, the next nearest star [Proxima Centauri] would be four miles away.
Proxima Centauri [right, photographed by Hubble Space Telescope WFPC2] is part of the Alpha Centauri star system, the closest star system and planetary system to Earth's Solar System at 4.37 light-years from the Sun. It is a triple star system, the other two stars as Sun-like and form a binary.

Proxima Centauri has two known planets, Proxima b, an Earth-sized exoplanet in the habitable zone discovered in 2016; and proxima c, a super-Earth, which is possible surrounded by a huge ring system, discovered in 2019.

α Centauri is the designation given to Alpha Centauri by Johann Bayer in 1603.

Alpha Centauri C was discovered in 1915 by Robert T. A. Innes.

Alpha Centauri is listed in Ptolemy's star catalogue. In his time it was visible from Alexandria, Egypt, but due to precession it can no longer be seen from that latitude.

The binary nature of Alpha Centauri AB was recognised in 1689 by Jean Richaud.


[20 December 2020] "SETI Detected a Strange Radio Signal From Proxima Centauri"

  • The Moon's diameter = 3,500 km
  • The Moon's mean distance from Earth is 384,000 km
  • Saturn has seventeen 82 known satellites/moons.
Saturn has 82 known moons, 53 of which have formal names. In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40500 meters in Saturn's rings, which are not considered to be true moons.

Titan, the largest moon [seen in the bottom left of the above image], comprises more than 90% of the mass in orbit around Saturn, including the rings. Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own, along with a tenuous atmosphere.

  • The asteroids are below 1000 km across.
  • Meteors - grains of sand-size.
  • Meteorites - larger, crater-causing, more like asteroids.
  • Light-year = 9.46 million million km.
  • Pole star - 680 light-years away
  • 100,000 million stars in our galaxy.
  • Nebulae = patches of cloud and dust / Latin for "clouds".
  • Andromeda's [bared] spiral galaxy is over 2 million light-years away.
  • Apart from a few of the nearest systems, all galaxies are moving away from us; the universe is expanding.


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