P7 Keywords Flashcards
solar day
The average time it takes for the sun to cross the sky (24 hours on earth)
celestial sphere
an imaginary sphere with the earth at its centre and the stars fixed to the surface of the sphere
sidereal day
When a day is measured by the movement of the stars (earth day would be 23 hours 56 minutes)
retrograde motion
when plants appear to slow down and go into reverse instead of moving from east to west (similar path to sun and moon) as usual.
solar eclipse
when the moon is perfectly aligned to block the suns light from reaching Earth
lunar eclipse
when the Earth moves into the moons shadow
angular size
an angular measurement describing how large a sphere or circle appears from a given point of view. (the sun is 400x the diameter of the moon and is also 400x as far away meaning they coincidentally have the same angular size)
optical telescopes
Were the first telescopes and use visible light
aperture
a hole or an opening through which light travels, the size of the aperture is dependant on how clear far away images appear
converging lenses
is curved on both sides. This means the light rays coming out of it come together at a point – they converge.
principal axis
A horizontal line passing through he centre of the lens
refraction
When Light changes direction when it passes at an angle from one material to another.
When light speeds up as it passes from one material to another, the angle of refraction is bigger than the angle of incidence.
focal length
The distance from the centre of the lens to the focus
dioptres
A mathematical unit used to measure the power of a lens
eyepiece lens
The lens next to your eye, it is the smaller but stronger lens
objective lens
The lens next to the object, it is the larger but weaker lens
spectrometer
used to measure the amount of radiation received at different frequencies
angular magnification
the ratio of the angle subtended at the eye by the image formed by an optical instrument to the angle subtended at the eye by the object being viewed.
prism
a triangular block
dispersion
the splitting of white light into colours
grating
a set of narrow parallel lines on a shiny surface, when light shines on it, different colour emerge at different angles produce several spectra.
Diffraction
When the aperture of a telescope causes blurring to the image by the waves spreading.
(It can be stopped by having an aperture much large than the wavelength)
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
Parallax angle
The parallax angle is the angle between the Earth at one time of year, and the Earth six months later, as measured from a nearby star. Astronomers use this angle to find the distance from the Earth to that star.
parsec
a unit of distance used when measuring parallax angles
luminosity
A power output; it is the energy it gives out each second by radiating light and other types of electromagnetic radiation
nebula
a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.
globular cluster
a spherical collection of stars that orbits a galactic core as a satellite
comet
a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun.
asteroid
a small rocky body orbiting the sun. Large numbers of these, ranging in size, are usually found between the orbits of Mars and Jupiter
planetary nebula
a ring-shaped nebula formed by an expanding shell of gas round an ageing star
supernova
This is when fusion stops in a red super giant so the mass collapses and causes a huge explosion (supernova) that will either form a neutron star or black hole
neutron star
made after a small supernova, it is a star consisting entirely of neutrons mad when the protons and electrons essentially fuse together during the explosion
black hole
From the product of a large supernova it is a region of space having a gravitational field so intense that no matter or radiation can escape (vacuum)
supernova remnant
This is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion
