Universe Guide

Glossary of Space Terms


Absolute Magnitude

This is the apparent magnitude a star would have if it was a mere 32.6 light years from Earth.


Antimatter is a grouping of anti-particles. An antiparticle is similar to a normal particle in size/mass but its charge and spin rotation is opposite to its normal particule. If a normal matter and anti-matter were to colide, they would obliterate each other. A lot of science fiction talk about anti-matter as being a source of energy when mixed with normal matter. In the Star Trek episode 'Alternative Factor' , Kirk visits an alternate universe which is based around the principles of anti-matter.


The point at which an item on a elliptical journey is furthest from the centre. Mainly talked about when the centre is the Sun. The oppostite is called a Perihelion.


It is a galaxy that has no identifiable shape such as a spiral galaxy or a elliptical galaxy. An example of an Irregular Galaxy is m82

Apparent Magnitude

This is how bright the star is as seen from Earth. The smaller the magnitude is, the brighter a star is in the night sky. A star of -3 is brighter than a star with a magnitude of 3. The faintest stars that can be seen without any aids is a 6.


Any body of rock that travels round the Sun between Mars and Jupiter. There are some exceptions to the rule where their path is either further out or nearer. For more information check out the dedicated page on Asteroids.


An astronaut is a term used for a Russian in space. The only difference between a cosmonaut, astronaut and a taikonaut is whose technology the person used to get into space.

Astronomical Unit (AU)

The average distance between the Earth and the Sun. This is equivalent to 149,598,000Km ( 92,956,000 miles ).


Fluctuating light that occurs when solar particles hit the atmosphere. They are seen mainly in the very northern hemisphere ( Aurora Borealis ) and the very southern hemisphere ( Aurora Australis )


Big Bang

The widely held view amongst many scientists as to how the Universe came into beginning. The theory says the universe began with an explosion. Another theory is the Solid State Theory which had been put forward by Sir Fred Hoyle. The term Big Bang was coined by Fred Hoyle as an insult to the theory but it cottoned on and became the accepted name for the theory.

Binary Star

Binary Stars are two stars that orbit round one another because of a mutual gravitational point. An example of a binary star is Algol .

Black Hole

Antimatter is a grouping of anti-particles. An antiparticle is similar to a normal particle in size/mass but its charge and spin rotation is opposite to its normal particule. If a normal matter and anti-matter were to colide, they would obliterate each other. A lot of science fiction talk about anti-matter as being a source of energy when mixed with normal matter. In the Star Trek episode 'Alternative Factor' , Kirk visits an alternate universe which is based around the principles of anti-matter.A Black Hole is the believe remnants of a collapsed star. Its gravity is so strong that not even light can escape from its pull. For more information, please check the dedicated black hole on the subject.

Blue Shift

Blue Shift is the opposite to Red Shift. When you look at the spectral value of a source of light, blue prominence will mean the object is moving towards the viewer.

Blue Star

These are the biggest stars in the Universe and the hottest too. They are over 16 times the Mass of our Sun and examples are Zeta Puppis and Zeta Orionis.



A comet is a ball of ice and water that travels through space on a path that will take it round the Sun. When it approaches the Sun, it lets off a vapour tail and some of these can be seen from the Earth. Its period can range from 3 years to over 40,000 years. For more information, check out the dedicated comets page.


A constellation is a group of close stars that represent a person ( e.,g. Hercules ), an animal ( e.g. Leo ) or an object ( e.g. Sextants ). For more information, visit my Constellations page for more information.


The corona is the outermost part of a Sun's atmosphere. It arches out from the main atmosphere. If you've ever seen the opening titles of Star Trek:Voyager, you will see the craft fly through a corona. It can't be seen from the Earth unless there is a solar eclipse.


A cosmonaut is a term used for a Russian in space. The only difference between a cosmonaut, astronaut and a taikonaut is whose technology the person used to get into space.


The results of either a meteorite smashing into a rocky surface leaving a hole. The other type is volcanic crater caused by the left overs of an eruption.


Dark Energy

Dark Energy like its "cousin" Dark Matter can't be detected directly but is known to have an effect on matter that can be detected.

Dark Matter

Dark Matter, you can't see it, you can't find it but you know its there because of its effect on the Matter that can be detected. It is widely said that it makes up the majority of matter in the Universe.


The Declination is equivalent to the latitude reading on Earth but is for space instead. Imagine Earth on a sheet of paper at the centre, the delination is how far to the up the page from planet the object would be. Declination is measured in degrees.



Measure of how much an ellipse deviates from a circle. The range of values start from 0 ( a perfect circle ) to 1 ( very elliptical )


When an object moves in front of another so as to block its view. In terms of space, there are two main ones, lunar and solar. In a Lunar Eclipse, the Earth blocks out the moon and is common. In a Solar Eclipse, the moon moves in between the Earth and the Sun. For more information, read Eclipses .

Escape Velocity

The escape velocity is the speed at which an item needs to be travelling in order to reak from the other objects with a stronger gravitational pull.

ExtraSolar Planet

An extra-solar planet or exoplanet for short is a planet that has been discovered round a distant star. An extrasolar planet can be either a gas giant like Saturn or a rocky planet like Mars. It might have an ecosystem like Earth. You can read more on my page on Extrasolar Planet.


Fission ( Nuclear )

Fission is the process of splitting atoms to release energy. It is the process that is used in nuclear power stations and atomic bombs around the world. Scientists are trying to move away from this technology in favour of Nuclear Fusion.

Fundamental Forces

Used to generically call the four fours that make up the Universe. At the beginning, they were altogether but then split up as the Universe began. The four forces are Gravity, Weak Nuclear, Strong Nuclear and Electromagnetic.

Fusion ( Nuclear )

Nuclear Fusion is the process of where atoms join together to make heavier items. It is at the core of how the Sun creates energy. The process converts Hydrogen into its slightly heavier Helium gas. It is currently the holy grail of international scientists who believe it will produce limitless energy forever.



Galaxy is a large collection of stars, clouds and gas amongst other things. They can come in many types, here are some of the more well know :- spiral ( Andromeda , Milky Way ), elliptical ( M87 ) and irregular ( M82 , Tadpole Galaxy ), Lenticular Galaxy ( NGC 3115 ) .

At the centre of most galaxies, ours included is believed to be a super black hole, other galaxies. At the centres of some galaxies, there is just a close group of stars.

Our galaxy is the Milky Way, the nearest neighbour is the Andromeda Galaxy and the further I know of is the Tadpole Galaxy. The Tadpole's shape is the result of two galaxies crashing into one another.

Gemini Program

The Gemini missions was N.A.S.A.'s attempt at putting a two man vehicle into space. It is named after the zodiac constellation Gemini which are the twins.


Gravity is an invisible force that attracts one object to another. The Earth has a gravity force keeping people on the ground. Other objects have a stronger force such as the Sun which keeps the planets orbitting round it. Due to its size, Jupiter has the power to pull the Sun off centre as it orbits. This principle is used to find gas giants cicling other stars. Earths gravity in comparisons is always 1. Weaker gravitational pulls have decimals values. As artificial gravity has not yet been discovered / invented, people will float when not secured down in a spaceship. Sir Isaac Newton first came up with the idea of Gravity when he saw an apple fall from a tree and wondered why,



The point of space where the stars solar winds and magnetic fields are affected by the interstellar winds.


The area of space where the star's solar winds and magnetic fields are confined by the interstellar winds. Could say they it is area which the solar winds and magnetic fields are effective.


A widely used scale for describing stars ranging from Supergiants to Dwarfs.


The most common gas in the universe, it makes up over 99% of the Sun's ingredients.


Irregular Galaxy

An irregular galaxy is a galaxy that has no defined form or shape. An example of one is M82 .


Jovian Planets

Another term for the Gas Planets, Jupiter, Saturn, Uranus and Neptune. All those planets have the same composition and are relatively close together in location to the Sun.


Kuiper Belt

An area of space that consists of lumps of rock that orbit the Sun. Similar to the asteroid belt between Mars and Jupiter. The most prominent object in this region is Pluto and Sedna. It is named after Gerard Kuiper who predicted its existance in 1951 but he wasn't the first to talk about this region of space. Irish astronomer Kenneth Edgeworth first suggested its existance. For more information, visit the dedicated kuiper belt page.


Lenticular Galaxy

In simpliest terms, it is like a convex lens where the middle bulges out. An example is ( NGC 3115 ) .


A light year is the distance light travels in a year. It is equivalent to 9,460 Billion Kilometers or 5,878 Billion Miles. It is a measurement of distance not time which some people might think.


Magnetic Field

A region of space that surrounds an object with a magnetic core. This magnetic field can protect the object from harmful rays from typically its local star. If Earth didn't have a magnetic field, then life would not have been able to survive on here. Mercury also has a weak magnetic field but Venus and Mars are not known to have such a field.

Mercury Programme

The Mercury missions were N.A.S.A's first missions to get people into space. The capsules consisted of one person which then led to the Gemini Missions which contains two people.


Classification devised by French Astronomer Charles Messier for far off objects. These Messier numbers have been given to galaxies, star clusters and nebulas. A large number of Messier's have proper names such as M32 is better known as the Andromeda Galaxy.


A meteorite is a meteor that didn't burn up in the upper atmosphere but landed on Earth. It might have created a crater if its large enough or made no physical impact. They usually consist of rock and iron. For more information, visit my dedicated Meteors page.


A meteor is when a rock/dust hits the upper atmosphere and burns up causing a streak of light. They can appear at any time ( sporadic ) or as part of a shower usually when the Earth passes the tail of a comet. For more information, check my dedicated meteors page.


A piece of rock/iron or anything travelling through space that isn't on a determind part like a comet or an asteroid. When it hits the atmosphere, it becomes a meteor and if its not burned up then it becomes a meteorite. For more information, visit my dedicated meteors page.

Milky Way

The name given to the galaxy that our solar system is in. It is spiral in formation with our solar system in the suburbs. The centre of our galaxy is toward the Sagittarius constellation.


A moon is any natural satellite orbiting a planet. Earth's moon is known imaginatively as 'The Moon'. Moons can either have been created from the planet it orbits as our one was. They could be asteroids that flew too close to planet and was caught by the planets gravity such as phobos and Deimos . Finally they could be formed in the same way as planets in their own way such as Titan or Europa but orbit a planet instead of the Sun. Most moons are dead, lumps of rock with no atmosphere. Titan on the other hand has an atmosphere and Europa has a hard surface with possible liquid underneath.



N.A.S.A. is the United States primary space exploration government body, it is a civiliian organisation but part of its work is top secret.


A Nebula is a large expanse of gas and dust. There are three types of these. Emission Nebula are extremely bright and can contain stars within. Reflection Nebula don't contain a star but its light is caused by a star nearby. Dark Nebula blocks all light from stars behind.

Neutron Star

The result of a supernova explosion. It consists of tightly packed neutrons and are quite small but have the same mass as our Sun.


Oort Cloud

A theorized cloud that exists over a light year from the Sun where comets are currently being held before being sent on their way to the Sun. Named after Jan-Hendrik Oort. The cloud is also known as Opik-Oort after Ernst Opik who said the cloud was just outside our solar system where the Kuiper Belt is. For more information, read my Oort Cloud page.


The path of one object around another. The Earth orbits the Sun, it moves round the Sun.

Orbit Eccentricity

The orbit eccentricity is the amount at which a circle or ellipsis deviates from a perfect circle. If the value is zero, it is a circular orbit, if the value is between 0 and 1, then the orbit is an elliptical. When the value is 1, it is a Parabola, greater than 1 is a Hyperbola which may look like a ellipse at one side but the end doesn't close.



The point at which an object that is orbitting Earth is at its closest. The opposite is Apogee .


The point at which an object is orbitting the Sun is at its closest. The opposite is Aphelion .


Pioneer is the name given to the American satiellite programme that aimed to send a satellite into space. The most famous of these is Pioneer 10 whose contact has been lost since 27th April 2002. Also means someone who progresses a field of science such as the Wright Brothers who pioneered flight.

Planetary Nebula

A star that is at its late stage of evolution with a bright shell of gas. A good example is the Ring Nebula ( M57 ). It can be viewed on the M57 page.


An object in space that orbits a Star. There is an ongoing discussion as to what a constitutes a planet. A planet can be rocky e.g. Earth or gaseous Jupiter. Pluto was deemed a planet when it was first discovered but since then other objects that are bigger than Pluto have been discovered beyond the orbit of Neptune such as Eris and Sedna. Eris and Sedna have not been given planet status.



Generic term used to describe a physical item that can interact with all the four fundamental forces ( Electromagnetism, Gravity, Strong Nuclear, Weak Nuclear ). Them and Leptons make up the basic components of matter. \r\nThere are six different types of Quarks ( Up, Down, Strange, Charm, Top and Bottom ). There are also anti-quarks which react in the opposite way.


The name comes from being a shortened version of QUASi-stellAR radio source. They are the active nucleus of a galaxy that is extremely bright and distant. They can appear almost star like when viewed.


Radio Galaxy

A Radio Galaxy is one that active galaxies that are very bright at radio wavelengths. An example of a Radio Galaxy is M87 .

Red Dwarf

On the Hertzsprung-Russell scale, the Red Dwarf is at the lower end of the scale, small, cool and not as bright.

Red Shift

The red end of a light spectrum that is proportionate to an object which is receeding.

Reflecting Telescope

Concave mirror are used to reflect light to a single point to form the image of an object.

Refracting Telescope

Refracting telescope is where the light is bended to a point to view the object.

Right Ascension

The Right Acension is equivalent to the Longitude reading on Earth but is for space instead. Imagine Earth on a sheet of paper at the centre, the right ascension is how far to the right of the planet the object would be. The Right Ascension is measured in Hours and Minutes.

Rotation Period

Also known as the Sidereel Rotation Period is the time it takes for an object to rotate once on its axis in comparison to the stars.



A satiellite is an object that travels round another object. A satiellite may be natural ( a planet, a moon ) or artificial ( a man-made satiellite )

Semi-Major Axis

The semi-major axis of an object is the distance from the centre of a ellipsis to the farthest edge.

Difference between semi-major and semi-minor axis

Semi-Minor Axis

The semi-major axis of an object is the distance from the centre of a ellipsis to the nearest edge.

Sidereal Orbital Period

The time taken by one object to complete an orbit round another object relative to the background stars.

Solar Wind

Electrons and protons moving at high speed from the Sun acting like a wind. It is hoped by some people that they can harness this power to produce spacecrafts that sail on the Solar Winds. The solar winds exist in heliosphere but when they reach the heliopause, their power becomes diminished.

Solid State Theory

A theory put forward by Sir Fred Hoyle to say the Universe has always been here and always will.

Soyuz Program

The Soyuz missions is Russia's current vehicle it uses to transport cosmonauts and astronauts into space.

Space Shuttle

The Space Shuttle were the main way for N.A.S.A. to get people and satiellites into space. During this time, there were two losses, the Space Shuttle Challenger and Columbia. The crafts were retired and put on display at muuseums round the United States. For more information on the shuttles, visit the Space Shuttle page.

Star Classifications

Stars are grouped into 7 main group, each identified by a letter ( O , B , A, F, G, K, M ). O are the biggest and blue where as G is the group that our Sun falls into. Most of the M Stars are small but supergiants such as Antares and Betelgeuse also fall into this group.


The explosion caused when a star explodes at the end of its life. The star will become at least a million times as bright as it was before the explosion. The star will then become a neutron star.



A taikonaut is a term used for a Chinese person in space. The only difference between a cosmonaut, astronaut and a taikonaut is whose technology the person used to get into space.


A tool that can be used to study the stars. They come in two main varieties, reflecting and refracting, both of which are explained elsewhere on the glossary page. Galileo Galilei is widely credited as being the inventor of the telescope in 1609.



A term used to descibe anything in the sky that can not be identified. People associate UFOs with crafts from outer space.


Van Allen Belt

In 1958, American astronomer James Van Allen discovered a zone in the upper atmosphere that contained particles ( electrons and protons ) trapped in the Earth's magnetic field.

Variable Star

A star that varies its brightness. There are three types of variables, they are pulsating ( expands and contracts its brightness in a periodic way ), eruptive ( expands and contracts abruptly ) and cataclysmic ( caused by one or more explosions ).

Voskhod Programme

The Voskhod missions were the Russian's attempt at putting a two man craft into space, it was a failure.

Vostok Programme

The Vostok missions were Russia's first attempt at putting a space man into space. Both Yuri Gagarin and Valentina Tereshkova used these craft to get into space.


White Dwarf Star

A high temperatured dwarf star that has ceased producing nuclear energy. It is around the size of Eath.



Part of the electromagnetic spectrum that is between Ultra-Violet and Gamma Rays. Black-Holes and Exploding Stars are detected by looking for X-Rays.


Yellow Star

A relatively cool star (5,000->6000 K) of which our Sun is an example. It is cool compared to Blue Stars which are over 33,000K. They are also known as G Class stars.



The point in the sky that is directly above the object in question, maybe a person or an observatory for example.

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