Exploring starlight

Question 1

what is absolute magnitude

Answer 1

true brightness of a star

absolute magnitude is defined at the stars apparent magnitude if the star was 10 PC away from us

Question 2

what information can be obtained from a stellar

spectrum

Answer 2

chemical composition
temperature
radial velocity
sunspot or starspot cycle
wave length
revolution of a star

Question 3

Understand how stars can be classified according to spectral type

Answer 3

classified by their spectra (the elements that they absorb) and their temperature.

Question 4

What is the name of the technique used by astronomers to study the chemical composition of a star?

Answer 4

spectroscopy

Question 5

What is the name of the diagonal band running from top left to bottom right on a H-R Diagram?

Answer 5

main sequence

Question 6

what is 1 degree in arcmins and 1 arcmin in arcseconds?

Answer 6

1 degree = 60 arcmins

1 arcmin = 60 arcseconds

Question 7

what is apparent magnitude?

Answer 7

brightness of stars as observed from Earth in the night sky

Question 8

how is a star’s colour and spectral type related

to its surface temperature

Answer 8

The surface temperature of a star determines the color of light it emits.

Question 9

Understand the inverse square relationship between distance and brightness/intensity

Answer 9

light intensity is proportional to 1/d^2

Question 10

define magnitude

Answer 10

how bright an object appears to the naked eye

Question 11

Understand the term parsec (pc)

Answer 11

distance from earth to a star that subtends a parallax angle of 1 arc second

Question 12

how can you work out parallax angles and distance

Answer 12

parallax angle = 1 / d
d = 1 / parallax angle
if tan parallax = 1 / d
parallax = 1 / d

Question 13

Understand how a star’s life cycle relates to its position on the Hertzsprung-Russell diagram, for stars similar in mass to the Sun and those with masses that are much greater

Answer 13

OBAFGKM - O = hottest, M = coolest

Question 14

Understand the light curves of the following variable stars:
a short/long period
b eclipsing binary
c Cepheid
d novae and supernovae

Answer 14

short/long period - changes magnitude over several days or weeks.
eclipsing binary - dips, at 24 hours, stays at 2.5 luminosity till 60 hours then dips
cepheid - light they produce dip and rise over a short period of time, returning to the same luminosity a few days later.
novae and supernovae - When it explodes, the luminosity increases by many magnitudes. The star reverts back to its former brightness after a period of 30 to 100 days.

Question 15

Understand the causes of variability in the light curve of eclipsing binary stars

Answer 15

when one star is brighter than the other and darker star moves in front of it.

Question 16

Understand how Cepheid variables can be used to determine distances

Answer 16

compare the Cepheid variable’s apparent brightness with its intrinsic brightness. difference between observed and actual brightness yields the distance.

Question 17

Understand the structure of gravitationally bound stellar groupings such as binary stars and clusters

Answer 17

binary stars - two stars that orbit around a common centre of orbit.
clusters:
open - groups of stars close to each other in space. usually very bright, found around galactic plane
globular clusters - spherical shaped with more stars nearer the nucleus. located around the galactic nucleus

Question 18

Understand how the period of an eclipsing binary star can be deduced from its light curve

Answer 18

from when the luminosity dips

Question 19

what are most modern astronomical observations recorded with?

Answer 19

digital sensors that convert light into electrical

signals, which can then be processed and stored as data files

Question 20

what radiation does the earth’s atmosphere not block out?

Answer 20

visible light and radio waves

Question 21

what can only be located at sea level on the Earth’s surface

Answer 21

only optical and radio telescopes should be located

at sea level on the Earth’s surface

Question 22

Understand how astronomers obtain and study the patterns of spectral lines in the light from astronomical objects

Answer 22

when looking at stars with a spectrometer, the spectrum tells us what atoms are present in the star and what atoms are absorbing the light

Question 23

Understand why radio telescopes need extremely large apertures in order to maintain a useful resolution

Answer 23

the larger the diameter, greater the resolution

wavelength of radiowaves are very long

Question 24

Understand how multiple radio telescopes can operate as an aperture synthesis system (array)

Answer 24

when they connect to other dishes, they give a greater resolution and and use the process of interferometry to combine signals

Question 25

what has radio astronomy been important for?

Answer 25

discovery of quasars, jets from black holes, the structure of the Milky Way and protoplanetary discs

Question 26

what has infrared astronomy been important in?

Answer 26

discovery of protostars, dust and molecular clouds and

hotspots on moons

Question 27

Understand the detrimental effect of the Earth’s atmosphere on the quality of images formed by telescopes on the Earth’s surface

Answer 27

The Earth’s atmosphere blocks all X-rays from space, so space telescopes must be used to observe in these wavelengths

Question 28

Understand why telescopes operating outside the optical and radio ‘windows’ need to be sited above the Earth’s atmosphere

Answer 28

Less infrared light penetrates to the surface so a higher location is better
to study x-rays and gamma rays

Question 29

Understand the advantages and disadvantages of space telescopes and detectors, including orbital observing platforms

Answer 29

advantages:
clear observations
wider wavelengths of em spectrum
no limitations to observing at night time
disadvantages:
expensive
maintenance is difficult

Question 30

Understand how gamma ray, x-ray and ultraviolet astronomy have been important in the discovery of gamma ray bursts, black hole accretion discs and the corona and chromosphere structure of young stars

Answer 30

Ultraviolet observation lets us study the chemical make-up and temperature of stars and lets us see stars at different stages of their evolution. sun is observed in UV to see corona and chromosphere in detail.
strong gravitational forces that surround a black hole can be observed in the x-ray part of the spectrum.

Question 31

Understand how a telescope alters the appearance of:
a stars
b double stars
c binary stars
d open clusters
e globular clusters
f nebulae
g galaxies

Answer 31

a) appears as dots of light to naked eye - telescope: sharper dots of light
b) naked eye - Appear as single star. Telescope: Viewed as multiple stars
c) naked eye - Can just be seen as two stars in dark light. Telescope: Viewed as multiple stars
d) naked eye - Faint stars in close proximity. Some individuals can be seen. Telescope: Numerous individual stars can be seen
e) naked eye - Appear as vague ‘blur’. Telescope: Detailed numerous stars can be seen
f) naked eye - Appears as small but slightly brighter ‘blur’. Telescope: Shape is more detailed. Colours are more obvious.
g) naked eye - difficult to view. Telescope: brighter and detailed view

Question 32

Explain the connection between the dark absorption lines and the chemical composition of the star

Answer 32

light passing through outer layers is made of all wavelengths/energies. some of this light has correct wavelength to excite atoms in stars outer layers. when atoms de excite they emit radiation of same wavelength

Question 33

what are the 7 types of the electromagnetic spectrum

Answer 33

radio waves, microwaves, infra red radiation, visible light, ultra violet light, xrays, gamma rays