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The very thin gas and tiny specks of dust that lie between the stars.
A subset of heavy metallic elements, such as iron, chromium and nickel that are the endpoints of nuclear fusion reactions in massive stars.
Atoms with the same number of protons in their nuclei but different numbers of neutrons are called isotopes. Because they have the same number of protons, they have the same atomic number and are atoms of the same chemical element. But because of the different number of neutrons, they differ in mass number.
The region of the Solar System, beyond the orbit of Neptune, containing many icy-rocky bodies, including dwarf planets (such as Pluto) with relatively low inclination orbits. The Kuiper Belt is sometimes called the Edgeworth-Kuiper Belt and is a sub-set of trans-Neptunian objects.
The grouping of galaxies in the neighbourhood of our galaxy. It contains about 40 known galaxies including the Milky Way and all the other galaxies within about three or four million light years.
The supercluster of galaxies centred on the rich Virgo cluster of galaxies and including the Local Group as an outlying constituent.
The amount of power emitted by a luminous object such as a star or galaxy, in the form of light or other electromagnetic radiation. It is related to the observed brightness of an object by the relationship: luminosity is proportional to brightness multiplied by distance squared. Luminosity may be measured in the unit of watts.
An historical, logarithmic scale devised to represent the observed brightness of astronomical objects such as stars.
The portion of the lifetime of a star during which it produces energy via the fusion of hydrogen to helium in its core. A star will remain on the Main Seqeunce for the majority of its total lifetime.