Bob the Alien's Tour of the Solar System
Space A - Z A B C D E F G H I J K L M N O P Q R S T U V W XYZ
Space A to Z

X, Y, Z

Word Meaning
X-ray A type of electromagnetic radiation that the Sun produces. X-rays cannot be seen, but are very powerful and can penetrate solid objects.
Xena Dwarf planet Eris was discovered in January 2005 but until it received its official name in August 2006, it was informally referred to as Xena. Its name was inspired by the title character in the TV show, Xena: Warrior Princess.
Year The length of time it takes for an object, usually a planet, to complete an orbit of the Sun.
Yellow Dwarf star A yellow dwarf is a star like the Sun. It is a main sequence star, meaning that it has formed and is going through is usual day-to-day existence of making heat and light by converting hydrogen into helium. Yellow dwarf stars are actually usually white. The Sun only appears yellow due to filtering in Earth's atmosphere. Yellow dwarfs usually stay in their yellow dwarf-like state for about 10 billion years, before heating up and expanding to become a red giant, and eventually eventually becoming a small white dwarf. A yellow dwarf might also be known as a G-type main sequence star.
Ymir A moon of Saturn, discovered in 2000 by a team of astronomers led by Brett James Gladman at the Côte d'Azur Observatory. It has a diameter of about 18 kilometres (11 miles) and takes over 3 and a half Earth years to get around Saturn. It received its name in 2003, named after a creature in Norse mythology. Ymir was a giant and the ancestor of all of the frost giants, two of which (a son and a daughter) were born from his armpits. Lovely. Even better, his feet gave birth to another son, a six-headed monster.
Al-Zarkali, Abū Ishāq Ibrāhīm Full name Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Zarqālī, Al-Zarqālī, or Arzachel, was an Arab astronomer and astrologer who lived in what is now Spain during the 11th Century. He made several accurate measurements about the motions of the Sun, known planets and Moon. Back then, it was thought that Earth was at the centre of the solar system. A lot of his calculations held true until later astronomers realised that it was actually the Sun at the centre of the solar system. He has a crater named after him on the Moon.
Zenith Look up, straight up. The point in the sky directly above you is the zenith.
Zodiac The Zodiac is the part of the sky that contains the constellations that are situated along the ecliptic, the path that the Sun appears to take across the sky as a year passes (in reality, it is Earth's changing position throughout the year as it orbits the Sun that causes the Sun to move through the constellations). The constellations, or signs of the Zodiac, are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Saggitarius, Capricorn, Aquarius and Pisces. The constellation that the Sun was passing through when you were born is what determines your star sign.  Astrologers believe that a person's destiny is based on their star sign and the changing positions of the objects in the night sky. But astronomy and astrology don't mix too well, so we'll say no more about it. .
Zöllner, Johann Karl Friedirch German astrophysisist who made the first measurement of the apparent magnitude of the Sun, being only 0.1 out. He also studied optical illusions and the paranormal. He lived from 1834 to 1882. There is a crater on the Moon named after him.
Zwicky, Fritz Swiss astronomer who worked at the California Institute of Technology. He and his colleague Walter Baade came up with the term supernova to describe the explosion of a dying star and their resultant neutron stars. He "observed" dark matter and calalogued loads of galaxies. He lived from 1898 to 1974 and has both a crater on the Moon and an asteroid named after him.

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