P1bL10 Searching Space

Key Words

Distance - How far it is from one object to another (really?)

Escape velocity - speed a rocket must travel to escape the gravity filed of a planet.

Gravity - a weak attractive force between all objects that have mass.

Hubble Telescope - A telescope orbiting the Earth, named after the astronomer Edwin Powell Hubble (1889 - 1953)

Mass - any object that is made out of material has mass.

Optical telescope - telescope that uses visible light.

Orbit - path of a satellite round a planet.

Orbital velocity - the speed at which a satellite has to travel to maintain a particular orbit.

Radio telescope - A radio receiver with a large parabolic reflecting disc

Reflecting optical telescope - a telescope which picks up the light with a concave mirror rather than a lens.

Grade E

Astronomers use telescopes to observe the night sky (you can't see much of space during the day).  The simplest optical telescope is a long tube with a lens at each end.  Binoculars are two of these simple telescopes mounted side-by-side.  While you can see a certain amount of space through binoculars, holding the things still is a pain.  You can, of course, buy a tripod. 

Astronomers have used big optical telescopes to view the night sky, but have run into all sorts of problems:

• Light pollution from nearby towns (a real problem in the UK);
• Cloudy skies;
• Distortion due to the atmosphere (which makes stars twinkle).

One answer is to build telescopes on the tops of high mountains:

• They are well away from cities;
• The air is thinner, so less prone to distortion;
• There are fewer clouds;
• It's cold, so the air is more stable.

Another answer is to take a telescope up in a high-flying aeroplane.  Steadiness depends on the skill of the pilot.

The Hubble Space Telescope is in orbit around the Earth.  Here there is no problem with atmospheric distortion and extremely clear images have been made.  Pictures show that there are even planets outside the Solar System.   

Satellites like the Hubble Space Telescope are held in orbit because of gravity.

Gravity is a force that always attracts (pulls).  It never repels (pushes away).  All objects that are made of any material have mass.  Therefore they feel the pull of gravity.  Gravity is a very weak force.  We can only feel it when the objects are very big, like stars and planets.

Gravity gets less the further you are away from big objects.  Double the distance, the gravity is four times less.

Nobody knows why objects have gravity.                                            

Grade C

The problem with lens telescopes is that even a wide lens does not allow enough light through to view really distant objects.  Also big lenses are quite hard to make and can distort colours and images.  The answer is to use a concave mirror to focus the rays into the eye-piece.  This is done with a reflecting telescope.

More light is captured and this gives much clearer pictures.  The largest mirror is about 4 m in diameter.

The space telescope is of this kind:

Note the lid to keep space debris from making the mirror dirty.  When the Hubble Space Telescope was first sent into orbit, the mirror was out of focus.  Repairs had to be made at vast cost.

When space probes are sent to far distant places in the Solar System (and beyond), they have to travel fast.  They don't have very much fuel on them, so they can't use their rocket motors very much.  However they use the gravity of the moon and the other planets to make them accelerate.  Although they are falling towards these planets, they are travelling so fast that they miss the planets.

Grade A

Objects in space emit radiation across the whole electromagnetic spectrum.  Scientists use a variety of instruments to detect the objects:

.