Definitions for Space

These are some very basic definitions for the Space Topic

Universe: Sum total of everything that exists.
Galaxy: A basic building block of the universe that includes stars, star clusters, clouds of gas, dust and interstellar molecules.
Solar System: Is one or more suns surrounded by orbiting planets. Our solar system is composed of the sun, 9 known planets and at least 44 moons, thousands of “minor planets” (asteroids) meteors and perhaps billions of comets.
Sun: Dominant member of a solar system accounts 99% of the mass of the solar system. The sun is a giant star it produces heat and light. A big ball of plasma
Star: Principle components of galaxies. Living stars emit radiation across the electromagnetic spectrum.  Peak depends on the heat of the surface.
Planet: A relatively large body rotating in an elliptical orbit around a sun.
Moon: A natural satellite of a planet i.e. rotates around a planet. Moons do not produce their own light.
Mass: Mass is a measure of the amount of matter in an object. It is measured in kilograms. Wherever you go your mass stays the same.
Weight: Weight is the force of gravity acting on an object pulling it towards the centre of the Earth or any other large mass. Weight is a force and so is measured in Newtons. The weight of an object varies depending on where you are (which planet etc and how far you are from it’s surface, the further away from the surface the smaller is your weight)..
gravitational field strength : gravitational field strength, g, is the weight per unit mass. It is measured in Newtons per kilogram. It is the force of gravity or pull on each kilogram of mass.
Inertia: Inertia is the property of an object which makes it hard to get an object to move, or to stop a moving object. Inertia varies with mass, so the bigger your mass the bigger your inertia..
Acceleration due to gravity: All objects will acceleration due to gravity. On the Earth, close to the surface objects accelerate at 9.8 ms-2 .
Light year: The distance light travels in a year equivalent to 9.46 .

Light does not travel at an infinite speed. It takes time to travel. It is so fast that we do not usually notice, although out in space the distances involved are so big that light takes a reasonable amount of time to reach us.

Light travels at: 3 × 108 ms -1

Given that it takes 8 minutes for light to get from the sun, how far is it away is it from the Earth?

8 × 60  = number of seconds in minutes  = 480s

Each second light travels 3 × 108m

d= v t

d= 3 × 108   × 480  = 1.44 ×1011m

How far does light travel in one year?

1 year  = 365days

365days  × 24 = 8760 hours

8760 ×60 × 60  = 31536000s in one year

Distance travelled in 1 year, d = v t

d = 3 × 108 × 31536000     = 9.46 × 1015 m in one year = one light year

The light year (ly) is the distance light travels in one year.

Light travels at 3 × 108 ms-1

Source Time taken for light

to reach us

Distance (m) Working
Moon 1.2 s 3.6 × 108 1.2 × 3 × 108
Sun 8 min 1.44 × 1011 480 × 3 × 108
Next nearest Star 4.3 y 4.07 × 1016 4.3 × 9.46 × 1015
Other side of galaxy 100 000 y 9.46 × 1020 100 000 × 9.46 × 1015
Andromeda galaxy 2 200 000 yr 2.08 × 1022 2 200 000 × 9.46 × 1015
Continuous Spectra

Many light sources produce a continuous spectrum containing all the wavelengths of visible light, e.g. an ordinary light bulb.

Line Spectra.

Some light sources emit only some wavelengths. They produce a line spectrum. Each line corresponds to a particular wavelength.

Each chemical element has its own line spectrum pattern(so it is like a finger print!)

Line spectra can be varied using a spectro-scope in the classroom.

Line spectra are used to tell us about the chemical composition of the stars.



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