As you’re no doubt aware, the universe is an incredibly complicated entity. This means there’s a lot for you to learn. But don’t fret; we’ve got everything you need to know right here. To help you out, we’ve arranged each of the below sections in no particular order, with headers so you can dip in and out of them quickly depending on what you need to know. Happy revising!
Spherical aberrations, should you want to know, occur due to the curvature of a lens or mirror and it is most pronounced with lenses (or mirrors) of large diameters. The effect can be minimised by making both lens surfaces contribute equally to the ray deviations.
The event horizon
The event horizon is the distance up to which nothing can escape from a black hole. Eerie or what? The phenomenon occurs when the gravitational field around a black hole is so high that nothing — including light — can escape. Unless of course, it is a certain distance away.
The lens equation
When using the lens equation, you should remember that where f is the focal length, u is the object distance and v is the image distance (i.e. distance from the lens). It’s also important to consider what sign each term has. For a divergent lens f is negative, and if the image appears on the same side of the lens as the object, then v is negative (in this case one would obtain a virtual image).
All you need to know about charge couple devices (CCDs)
The quantum efficiency of a typical CCD is ~75 per cent. This quantum efficiency is the ratio of the number of photons incident on the device to the number of photons detected. Photographic film usually has a quantum efficiency of ~5%.
A charge couple device is a microchip that converts a light signal into a digital format. They act as a replacement for photographic film, and are wafer thin chips divided into individual picture elements called pixels. There are a handful of advantages over traditional photographic film; namely, CCDs are more efficient, and they can detect wavelengths beyond those of visible light, etc.
An Airy disc is the name given to the effect of a light passing through a circular aperture, which is analogous to that of it passing through a double slit, in that an interference pattern is produced whereby the diffracted waves (of light) interfere with one another and produce a series of light and dark rings (or fringes for the double slit)
Wien’s Displacement Law
Wien’s Displacement Law demonstrates that the peak wavelength is inversely proportional to the temperature in Kelvin.
The Doppler Effect
The Doppler Effect is the shift in wavelength of light (or sound), due to relative movement of source or observer. In astronomy, if a star and the Earth are moving towards one another, the wavelengths are shortened (moved to the blue end of the spectrum), so they are blue shifted. When they are moving away from one another, the wavelengths are lengthened (towards the red end), so they are red shifted.
Hubble’s law is the name given to the statement in astronomy that galaxies move away from each other, and that the velocity with which they recede is proportional to their distance. To put a long story short, we can thank Hubble’s Law and scientists’ extrapolations for the Big Bang Theory. Go science!
As far as your exams are concerned, you should know that where v is the recession velocity in kilometres per second H is Hubble’s constant, which has a modern value of 73 kilometres per second per megaparsec. Edwin Hubble determined this relationship by plotting the recession velocities of galaxies against their distance. This is a linear relationship, showing that the further away the galaxy, the faster it is moving away. The Hubble constant is the gradient of this relationship.