Observing the Universe (Edexcel GCSE Physics)

• Methods of observing the Universe have changed drastically over time
• Throughout history, astronomy has played an important role in human society
  • Not just because of mankind’s fascination with the heavens but also in navigation and agriculture

• Ancient astronomers split the night sky into constellations to help them remember the stars
  • They knew that some constellations only ever appeared in the northern skies, whilst others lay to the south

• They also aligned monuments with the position of certain stars or the position of the Sun on certain days of the year, and these helped them to keep track of the seasons
• One example is the Callanish Stones in the Isle of Lewis and Harris, Scotland
  • These are an arrangement of standing stones placed in a cruciform pattern with a central stone circle 13 metres (43 feet) in diameter
  • They were constructed specifically in line with the movements of the Sun and Moon, 5000 years ago

The Callanish stones were used to track the movements of the Sun and the Moon

Modern Telescopes

• The most important development in astronomy was the invention of the astronomical telescope in the early 17th century
• Early telescopes allowed astronomers to:
  • Observe the features of planets and moons for the first time
  • Develop more accurate models of the solar system, for example, the heliocentric model of the Solar System

• Modern telescopes provide much more data than the telescopes used hundreds of years ago, this is because:
  • They can detect more wavelengths/frequencies in the EM spectrum than just visible light
  • They can be positioned above the Earth’s atmosphere where less radiation is absorbed
  • They can detect weaker signals
  • They have a much greater magnification
  • They are much more powerful
  • Technology has improved so computers can process and improve the data

• Modern telescopes come in several shapes and sizes
  • These can range from smaller telescopes found in a classroom to giant radio telescopes, such as the Lovell Telescope based at the Jodrell Bank Observatory in Cheshire

Modern telescopes are a range of different sizes and can be on Earth on in space, depending on their use

Telescopes in Space

• The atmosphere can substantially restrict the quality of astronomical observations, such as:
  • Reflection of light from moisture in the atmosphere causing light pollution
  • Air currents distorting the path of starlight

• As well as this, not all electromagnetic radiation coming from space reaches the Earth’s surface
• The atmosphere absorbs certain wavelengths of electromagnetic waves restricting observations from astronomical objects that produce these, such as:
  • Near (short-wavelength) microwaves
  • Far (long-wavelength) infrared
  • Near (short-wavelength) ultraviolet
  • X-rays
  • Gamma rays

Some wavelengths of the electromagnetic spectrum are absorbed by the Earth's atmosphere

• To get around these problems, telescopes are often launched into space
  • The most famous of these is the Hubble Space Telescope (this detects UV, optical, and near-infrared)
  • Others include the Chandra X-ray telescope and the Spitzer infrared telescope

• The benefits of space telescopes are:
  • They lead to the discovery of objects not detectable by visible light
  • More information and data can be collected
  • Different EM waves can give different types of information about astronomical objects
  • They can produce much more detailed and magnified images
  • They produce clearer images which are unaffected by Earth’s atmosphere and light pollution

• The downsides of space telescopes are:
  • The telescopes are much harder to repair
  • They cannot be made too large since they need to fit into a rocket to be launched
  • They are much more expensive