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Space Physics 7.1 – Signals from Space The Universe The universe consists of many galaxies separated by empty space. Here is what makes up the universe in order of size. Term Meaning moon an object orbiting a planet (reflects light) planet an object orbiting a star (reflects light and produces no energy) star large ball of gases producing light & heat galaxy large ball of matter emitting light universe whole 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. v 3 10 8 ms -1 t 1 year 60 60 24 365 31.536 10 6 s d? d vt 3 108 31.536 106 d 9.5 1015 m (5,878,625,373,183.61 miles) It is difficult to comprehend such a large distance, so here are some times for light reaching Earth from various sources. Light Source Time Taken for Light to Reach Earth Moon 1.2 s Sun 8 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 Astronomical Telescope long focal length short focal length eye distant planet objective lens light-tight tube eyepiece lens 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. Ray Diagrams A ray diagram shows what happens when light passes through a convex lens. The convex lens is represented by a vertical line. Symbol Meaning 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) M F O 2F F object distance OM > 2F I principal axis The image is real, inverted and diminished. Example 2 (Magnifying Lens) M I 2F F O F principal axis object distance OM < F The image is virtual, upright and magnified. Magnifying An Image The object is closer to the lens than the focus. This produces a virtual image which is upright and magnified. M I 2F F O F principal axis M I 2F F O F principal axis 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. Colour Wavelength (nm) Red Orange Yellow Green Blue Indigo Violet 700 decreasing wavelength 400 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. v 3 10 8 ms 1 Each radiation in the electromagnetic spectrum has its own wavelength and frequency. vfλ Radiation Detectors Radiation low frequency long wavelength high frequency short wavelength TV and radio Detector aerials microwaves curved reflector & receiver infrared blackened thermometer visible light eye ultraviolet fluorescent paint x-rays photographic film gamma rays GM tube 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