Also referred to as ether.
A hypothetical medium to allow transmission of light, similar to the way the air acts as a medium to allow transmission of sound.
Following the Michelson-Morley Experiment it is generally accepted that this aether does not exist.

The point when a planet, following its orbital path, is farthest from the Sun.

The space program that took man to the moon in 1969, more information can be found in Space-Uplink's Space Race section.

An Astronomical Unit is the mean distance between the Earth and the Sun, i.e. the Earth orbits at a distance of 1 AU from the Sun. It is equal to 149,597,870.691 kilometers.

Chromatic aberrations are caused by the lens in a refracting telescope failing to focus different wavelengths of light (i.e. the different colours of the spectrum that make up white light) onto the exact same focal plane (i.e. it focuses them at slightly different distances). It's effect is to create a purple blurring on the images.
Today this is overcome by either using a double lens or, in large telescopes, by using process of reflection (mirrors) rather than refraction (lenses)

This effects both light and sound. It is caused by a change in wavelength of the sound or light as a object moves relative to the observer.
If the object is moving towards the observer the wavelength is compressed, if it moving away the wavelength is stretched.
The apparent effect for light is the objects visible light is altered, the spectrum is shifted towards blue if an object approaches (blueshift) and towards red if the object recedes (redshift). The effect for sound is a change in the pitch.
The amount of change is determined by the relative velocity of the object.

The study of the behaviour of motion on the Earth's surface.

Einstein's famous equation known as the energy-mass relation. This basically states that mass and energy are interchangeable, with the amount of energy released in conversion been equal to the mass converted multiplied by the speed of light squared. In other words a small amount of mass converted releases a tremendous amount of energy. Nuclear fission, nuclear fusion and the antimatter annihilation all produce energy in this method, in increasing orders of amount of mass converted.

Simply the amount of energy available in a specific quantity of propellant.

This refers to the 4 largest moons around Jupiter. Galileo was the first to discover them in 1640 and are thus credited to him in name.
The four satellites are known as Io, Europa, Ganymede and Callisto.
Interestingly these same satellites were discovered independently by Marius, and it is he who is responsible for their individual names.

Vision of the universe that places the Earth at it's centre and proposes that the whole universe revolves around it.

Gruppa Isutcheniya Reakivnovo Dvisheniya, or Group for Investigation of Reactive Motion. This was the USSR rocket organisation.

This theory places the Sun at the centre of our solar system, with the Earth, along with the rest of the planets, revolving around it.
This theory is, of course, long proved correct.

High velocity flight, once passing around Mach 5, i.e. around 5500 km/h, the vehicle is termed hypersonic.

The state in which an atom is missing one or more of its electrons, and is therefore positively charged. In an ionised gas some or all of the atoms are ionised, as opposed to being electrically neutral as is the norm.

A fundamental law of motion, which states the momentum of a system or an object is constant and cannot change due to any internal interactions. Or in other words the momentum will remain unchanged unless acted upon by an external force.

A body's mass would be constant on both the Earth and the Moon (and anywhere else for that matter), however a body's weight on the Moon would only be 1/6 of its weight on the Earth.
Why? Weight is simply the gravitational force exerted on a body and therefore it is determined by the strength of the gravitational field at your location. So the reason for the body's weight being 6 times greater on the Earth than the Moon is that gravity is 6 times stronger on the Earth's surface.

This is a rocket with two or more engines lined along its length. When the first engine burns out it ignites the next engine, then releases itself from the rocket and falls away.
You cannot use too many stages due to the excess weight the first engine would have to carry.

The term used to refer to anything that astronomers could not classify, for example when distant galaxies were first observed as 'fuzzy patches of light' and it was not known as to what they were they were simply labelled nebulae.
In modern times the word has been used to describe large clouds of gas in space (they can be huge - 10's of light years across!).
There are many different forms of nebula and their formation is often based on some stage of a star's life - anywhere from the formation of the star (such as the great Orion Nebula which is a region of star formation in the Orion system) until the death of the star (Planetary nebulae are clouds of gas blown free from a dying star and the Crab Nebula is a remnant of a star gone supernova in the Taurus system).

The break-even point for nuclear fusion occurs when you harness as much energy from the reaction as you put in to achieve the reaction in the first place. Currently we are well below the break-even point, i.e. it takes much more energy to create the reaction than can be obtained from the reaction.

The Oort Cloud is a massive spherical cloud of rocks and dust that may surround our solar system. It is thought to exist between 50,000 to 100,000 A.U. from the Sun and may contain anywhere from billions to trillions of comets.
It has not been directly observed, its existance is inferred from the orbits of the long period comets.

The point when a planet, following its orbital path, is nearest to the Sun.

A jet (air-breathing) engine that has no moving parts. Instead the air is compressed in the engine by the current speed of the aircraft. This means that the engine has a relatively narrow operating range, the craft must be supersonic to gain a high enough compression, with the upper limit being between Mach 4 and 5

The normal direction of a planets motion as we see it from Earth is West to East against the background of the stars. Occasionally, however, the planets outside the Earth's orbit can be seen, over a number of nights, to slow, eventually to stop and then to reverse direction (i.e. East to West against the background) for a time! They will then appear to slow again, stop and resume their original direction.
This caused real problems for the geocentric theory, and Plotemy's attempts to explain the observed motion led to the theory becoming very complex.
The correct reason for this motion was first realised by Copernicus in his heliocentric theory, but it was not until Kepler produced his work that it was conclusively understood.
The correct theory is that as Earth's orbital velocity is greater than the planets outside it, so it will slowly catch up and overtake these planets. The effect of this as viewed from Earth is that their velocity across the sky will slow down as Earth closes in to 'overtake' it, as Earth is passing their path will seem to reverse for a short time and once passed the path will revert to its original course.

This is a Supersonic-combustion ramjet. Similar to the ramjet but provides correct compression at sustained hyersomic flight. Aircraft must be travelling over about Mach 4 for the scramjet to work. This engine should continue to accelerate all the way up to Mach 12-15.
The scramjet is not fully developed yet.

The semimajor axis is the distance from the centre of an ellipse to the most distant point on its perimeter.
Due to the Sun not being at the centre of a planet's elliptical orbit, but being offset, the semimajor axis defines a planet's average distance from the Sun.

A measurement for determining the relative performances of a rocket propellant that demonstrates how efficient the rocket is.
Specific impulse is basically equivalent to exhaust velocity, it is actually exhaust velocity divided by the constant g. As a result, specific impulse has units of seconds.
Physically, it is the number of seconds a rocket engine can produce one pound of thrust from one pound of fuel, so a specific impulse of 1,000,000 means that the engine gives 1,000,000 pounds of thrust, for one second, for every pound of fuel consumed.

The higher the specific impulse a rocket has, the less fuel it requires to produce a given amount of thrust.

Scanning Tunneling Microscopy (STM)
A type of scanning probe microscopy in which a very sharp tip is moved to within 1 nanometer of the sample. This starts a tiny tunneling current to flow between the sample and the tip, which is accurately measured to produce 3 dimensional topographs of the sample.

Atomic Force Microscopy (AFM)
This is very similar to the STM but here the tip actually physically rides over the sample and its tiny movements are recorded, again allowing a 3 dimensional topograph to be created.

Both of these techniques of microscopy are able to anaylse down to individual atoms and even move them with atomic precision, the limitation here is they may only move 1 atom at a time.

These are temporary areas of magnetic field concentration on the Sun's photosphere (the visible surface of the Sun). In these areas the magnetic concentration prevents the heat from the core of the Sun escaping to the surface, which results in the area being cooler. This is why these areas appear darker in the images.

Thrust is a measure of how much force an engine can push with, it is equal to the exhaust velocity x the propellant mass (mass exhausted by the rocket) every second.
More properly, we speak of a propulsion system's thrust-to-weight ratio (T/W). This gives the acceleration that the engine can produce in units of Earth gravities. E.g. 2g means an acceleration of 2 x 9.8 or 19.6m/s².

The German 'Society for Space Travel' that was to investigate rockets for use in space.