Astrophysics (13)

Question 1

Lens

Answer 1

can be used to refract light. Lenses are used to focus light and to produce images of various objects.

Question 2

The Universe

Answer 2

made up of billions of stars and galaxies. The distance between galaxies is measured in millions of light years. The Universe is about 13.8 billion years old.

Question 3

Converging lens

Answer 3

refracts rays of light to a point.

Question 4

Principal axis

Answer 4

the principal axis of a lens is an imaginary line that passes through the centre of a lens and through the centres of curvature of the faces of the lens.

Question 5

Focal point

Answer 5

the focal point of a lens is the point at which rays parallel to the principal axis of the lens are brought to a focus.

Question 6

Focal length

Answer 6

the focal length of a lens is the distance between the centre of the lens and the point at which rays parallel to the principle axis are brought to a focus.

Question 7

Collecting power

Answer 7

is a measure of the light intensity gathered by a telescope. This is proportional to the square of the telescope’s diameter.

Question 8

Brightness

Answer 8

the brightness of a star is a measure of how much visible light from the star reaches our eyes.

Question 9

Luminosity

Answer 9

the luminosity of a star is the energy it emits per second, in all wavelengths.

Question 10

Apparent magnitude

Answer 10

a star’s apparent magnitude is a measure of its brightness as it appears on the sky.

Question 11

Astronomical unit

Answer 11

the average distance from the Earth to the Sun (AU) = 1.5×〖10〗^11m (2sf).

Question 12

Light year (ly)

Answer 12

the distance travelled by light in one year = 9.46×〖10〗^15m.

Question 13

Parallax

Answer 13

nearby objects appear to move relative to far-away objects, when viewed from a different angle. If the measured parallax angle is smaller, then the distance to the star is further.

Question 14

Parsec (pc)

Answer 14

1pc = 3.26ly

Question 15

Absolute magnitude

Answer 15

a star’s absolute magnitude is the apparent magnitude the star would have if it were 10pc away.

Question 16

Black-body radiation

Answer 16

the type of electromagnetic radiation that is emitted by a black or non-reflective body, which is held at a constant uniform temperature.

Question 17

Absorption spectrum

Answer 17

this spectrum is seen as a series of dark lines in a continuous spectrum, when some elements absorb specific wavelengths of light.

Question 18

Main sequence star

Answer 18

a star in which hydrogen ‘burning’ takes place. This is the thermonuclear fusion of hydrogen nuclei into helium nuclei.

Question 19

Neutron star

Answer 19

a collapsed star made of neutrons. It has a very high density.

Question 20

Black hole

Answer 20

a highly condensed state of matter that has an escape velocity higher than the speed of light.

Question 21

Gamma-ray burst

Answer 21

a brief intense emission of gamma rays from a collapsing supergiant star.

Question 22

Schwarzschild radius

Answer 22

the radius of a black hole’s event horizon. Light cannot escape from inside a black hole’s event horizon.

Question 23

Standard candle

Answer 23

a star or supernova of known brightness that can be used to calculate galactic distances.

Question 24

The Doppler effect

Answer 24

the name given to the apparent change in the frequency, or wavelength, of a moving source of sound (or other type of wave).

Question 25

Cepheid variable

Answer 25

a bright star whose intensity varies over a matter of days. The period of the variation of intensity is linked directly to the absolute magnitude of the star.

Question 26

The Big Bang theory

Answer 26

the theory that the Universe originated about 13.8 billion years ago. All the matter we see in the Universe exploded at one point and has been travelling outwards ever since. In the first few seconds after the Big Bang, the Universe was extremely hot, with temperatures in excess of 1011K. As the Universe cooled, atoms of hydrogen and helium were formed. Over billions of years, the force of gravity acted on this matter to pull it together into the stars and galaxies that we see today.

Question 27

Quasar

Answer 27

a small, very distant object, which emits as much power as a large galaxy.

Question 28

Exoplanet

Answer 28

a planet outside our Solar System, in orbit around another star.