Cambridge IGCSE Physics6.2 Stars and the universe Checklist

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What's on this checklist

Core

  • I know that the Sun is a medium-sized star, made mostly of hydrogen and helium, and that it radiates most of its energy in the infrared, visible light and ultraviolet regions of the electromagnetic spectrum.
  • I can state that:a)each galaxy is made up of many billions of starsb)the Sun is a star in the galaxy known as the Milky Wayc)the other stars in the Milky Way are much further from the Earth than the Sun isd)astronomical distances can be measured in light-years, one light-year being the distance light travels through (the vacuum of) space in one year
  • I know that the Milky Way is one of many billions of galaxies that make up the Universe, and that its diameter is approximately 100 000 light-years.
  • I can describe redshift as an increase in the observed wavelength of electromagnetic radiation emitted by receding stars and galaxies.
  • I know that light emitted by distant galaxies appears redshifted compared with light emitted on the Earth.
  • I know that the redshift in the light from distant galaxies is evidence that the Universe is expanding, and that it supports the Big Bang Theory.

Extended

  • I know that one light-year is equal to 9.5 × 10¹⁵ m.
  • I can describe the life cycle of a star:a)a star forms from interstellar clouds of gas and dust that contain hydrogenb)a protostar is an interstellar cloud that is collapsing and rising in temperature because of its internal gravitational attractionc)a protostar becomes a stable star when the inward force of gravitational attraction is balanced by an outward force caused by the high temperature in the centre of the stard)all stars eventually run out of hydrogen as fuel for the nuclear reactione)when most of the hydrogen in the centre of the star has been converted to helium, most stars expand to form red giants, and more massive stars expand to form red supergiantsf)a red giant from a less massive star forms a planetary nebula with a white dwarf star at its centreg)a red supergiant explodes as a supernova, forming a nebula containing hydrogen and new heavier elements, and leaving behind a neutron star or a black hole at its centreh)the nebula from a supernova may form new stars with orbiting planets
  • I know that microwave radiation of a specific frequency is observed at all points in space around us, and that it is called the cosmic microwave background radiation (CMBR).
  • I can explain that the CMBR was produced shortly after the Universe formed, and that, as the Universe expanded, this radiation was expanded into the microwave region of the electromagnetic spectrum.
  • I know that the speed v at which a galaxy is moving away from the Earth can be found from the change in wavelength of its starlight caused by redshift.
  • I know that the distance d of a far galaxy can be found from the brightness of a supernova in that galaxy.
  • I can define the Hubble constant H₀ as the ratio of the speed at which a galaxy is moving away from the Earth to its distance from the Earth, and I can recall and use the equation H₀ = v/d.
  • I know that the current estimate for H₀ is 2.2 × 10⁻¹⁸ per second.
  • I know that the equation 1/H₀ = d/v gives an estimate of the age of the Universe, and that this is evidence for the idea that all the matter in the Universe was once present at a single point.