| 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. |
