Space Physics 7.1 – Signals from Space

The universe consists of many galaxies separated by empty space. Here is what makes up the universe in order of size. The Universe TermMeaning moonan object orbiting a planet (reflects light) planet an object orbiting a star (reflects light and produces no energy) starlarge ball of gases producing light & heat galaxylarge ball of matter emitting light universewhole of space that can be detected

Light Year A light year is a distance. It is the distance travelled by light in one year. Example Calculate the length of one light year. (5,878,625,373, miles)

Light Source Time Taken for Light to Reach Earth Moon1.2 s Sun8 minutes Nearest start after the Sun (Proxima Centauri) 4.3 years Other side of our galaxy 100,000 years Our nearest galaxy (Andromeda) 2,200,000 years It is difficult to comprehend such a large distance, so here are some times for light reaching Earth from various sources.

Astronomical Telescope objective lens eyepiece lens eye distant planet light-tight tube The objective lens collects light and forms an inverted image of the distant planet which is magnified by the eyepiece lens. A larger diameter objective lens collects more light, so brighter image is formed. long focal lengthshort focal length

Ray Diagrams A ray diagram shows what happens when light passes through a convex lens. The convex lens is represented by a vertical line. SymbolMeaning M O F I OM IM optical centre of lens object focal length of lens image object distance image distance

Rules 1.A ray parallel to the principal axis passes through the focus after refraction. 2.A ray passing through the centre of the lens continues straight on undeviated. Image Three facts should be stated about an image. Is it: 1.real or virtual 2.upright or inverted 3.magnified or diminished or same size

Example 1 (Camera) Example 2 ( Magnifying Lens ) F F 2FO IM principal axis F2FO MF principal axis I The image is real, inverted and diminished. The image is virtual, upright and magnified. object distance OM < F object distance OM > 2F

Magnifying An Image The object is closer to the lens than the focus. This produces a virtual image which is upright and magnified. F2FO MF principal axis I

F2FO MF principal axis I

The Visible Spectrum White light is made up from a range of colours. A prism will split white light into its component colours, by refraction of the white light. ColourWavelength (nm) Red Orange Yellow Green Blue Indigo Violet decreasing wavelength

The Electromagnetic Spectrum Visible light is just a small part of a whole range of radiation known as the electromagnetic spectrum. Each type of radiation in the electromagnetic spectrum travels at the speed of light. Each radiation in the electromagnetic spectrum has its own wavelength and frequency.

Radiation Detectors RadiationDetector low frequency long wavelength aerials microwavescurved reflector & receiver infraredblackened thermometer visible lighteye ultravioletfluorescent paint x-raysphotographic film gamma raysGM tube TV and radio high frequency short wavelength

Detecting Signals Energy is omitted from objects in space at many different wavelengths. To get a full picture of our universe information of all wavelengths is collected. This is done using many types of telescope.

Radio Telescope Large unpolished metal dishes collect and direct weak radio waves to an aerial at the focus. To see fine detail, the opening of the radio telescope should be as large as possible. This is hard to achieve with one telescope, so several are usually used, and computer software combines the information.

The 305-metre Arecibo dish in Puerto Rico is the world's most sensitive radio telescope.

Microwaves Astronomers can detect radiation from space that has a wavelength of several millimetres. This can give information on the temperature of stars and hence their age. As the star reactions change, so will its temperature. Microwave ovens at home use microwave radiation which has a wavelength of about 12cm. Infrared Radiation Infrared radiation arrives on Earth from objects in space. Objects at different temperatures give off different colours of light. The hotter an object is, the smaller the wavelength of emitted light.

Line Spectra White light sources produce a continuous spectrum emitting all colours of the rainbow. Other sources of light, for instance street lights, emit only particular wavelengths of light. Line spectra tell us about a stars chemical composition, as each element has its own line spectrum pattern.

Example 1