Chapter 10 Flashcards
What is spectroscopy?
The measurement of the quantity of light energy at each wavelength or frequency
What can the emission/absorption lines indicate?
The composition of the emitter
What characteristics can be observed by the spectrum an object produces?
- Composition of the emitter
- internal motions
- processes occurring within the object
Why do wavelengths from space not necessarily conform to the laboratory standards?
There is a shift in the wavelengths formed by redshifts and blueshifts
What is a redshift?
A shift to a longer wavelength and lower energies. Often indicates that something is moving away from you
What is a blueshift?
A shift to a shorter wavelength and higher energy. Often indicates that something is moving towards you
What is indicated by an object that has both a redshift and a blueshift?
It is rotating
What is indicated by a star who is shifting back and forth?
It is in orbit around something
Why might we not be able to see something a star is orbiting from the spectroscopy?
The glare of the star orbiting it, which is brighter, masks the star being orbited
What is gravitational redshift?
This occurs when photons climb out of a strong gravitational field to a point where the field is weaker
What is a gravitational blueshift?
This occurs when light falls from a weaker to a stronger point in the field
What gravitational shifts would we see on earth and why?
Gravitational redshifts
The gravitational fields of the stars and galaxies from which the photons were emitted are much stronger than that of earth, so they are climbing out of a strong gravitational field
What is the cosmological redshift?
It is produced by the space-time geometry of the universe
It is a consequence of the fact that the universe is not static and stationary, but constantly changing and expending
What was Thomas Wright’s idea?
That the Earth and Sun lay on an enormous shell of stars
What did Kant hypothesise?
That the sun was just one point on a huge disk of stars. There were many other disks like it, all clustering together in groups of ever-increasing size
What were the fuzzy patches of light originally thought to be?
Nebulae, clouds of gasses
Who was the first person to compile and catalog nebulae?
Charles Messier
What was Messier’s mission/
He was trying to find the things in the sky that were not comets. This has inadvertently turned into a useful way of cataloguing nebulae
What did Herschel do?
He drew a diagram of the stars in the Milky Way. This placed the Sun somewhere near the centre of the elliptical disk of stars
What did Rosse discover?
He discovered that many of the nebulae have distinct spiral shapes. This was thanks to improved telescopes
What are spiral nebulae?
Nebulae that resembled whirlpools of light
What was the debate over these spiral nebulae?
Were they other galaxies completely or were they within the Milky Way?
Why did Herschel underestimate the size of the galaxy itself?
the dust within the Milky Way blocks our view through the galaxy
What is a nova?
An abrupt and temporary increase in the brightness of a star, sometimes they can be 100,000 times brighter than the sun
What is the issue with using supernovae to measure the distances?
finding supernovae is chancy, especially before the days of systematic searches of them
Also, 19th century astronomers did not know what a supernova was
What did Vester Slipher observe?
The spectral shifts (and therefore the radial velocities) of some of the spiral nebulae
He found that some of these nebulae had velocities great enough to supersede the escape velocity of the Milky Way
What did Slipher’s study indicate?
The island model of the universe
What did Van Maanen argue?
He said that direct rotation of the nebulae observed in a couple years, then the rotation would be faster than the speed of light if it was so far away
This was wrong, but it was a massive blow against the island theory
What did Shapley discover?
- That the sun was not at the centre of the milky way
- That the milky way’s diameter was 300,000 ly wide
Is the diameter of the Milky Way actually 300,000ly?
No, shapeless prediction was too large by roughly a factor of 3
What is meant by the cosmic distance ladder?
The way we measure distance depends on how we measure the distance of each thing before it
How can parallax be measured?
By finding the corresponding angle then using triangulation
What is an arc second?
1/3600 of a degree
What is a parsec?
3.26 light years
How is the Hipparcos satellite used?
it can accurately measure the parallax of over 100,000 stars
How is the GAIA satellite used?
It can accurately measure the distances to 1.33BN stars
Measurees distances of up to 10,000 ly away with an accuracy of 10%
How can knowing the luminosity of an object help is to calculate the distance?
We can rearrange the formula for the inverse square law of light to find the distance
What is a weakness of the use of the inverse square law of light formula?
It relies on knowledge of the absolute luminosity of the target object
What is a standard candle?
a term referring to any object of known luminosity
What is extinction?
The interference of dust in determining the actual luminosity of an object
what is a cepheid variable star?
a star that varies its luminosity regularly. This pattern can take just 90 minutes or days.
What did Leavitt discover about the cepheid variables?
The brighter the star, the longer the period
What did Hubble discover about the Andromeda galaxy?
By using its luminosity, he realised that it resided far outside the Milky Way
what were Hubble’s classifications for galaxies?
He classified them as spiral, elliptical
What is the Hubble Law?
That redshift is proportional to distance. There is more redshift the further away the object is
What is the slope of the line in Hubble’s graph plotting Brightness against Redshift called?
The Hubble constant
What are the current measures for the Hubble constant?
60km/s
What was Hubble’s initial value for H?
500km/s
Why was Hubble so off in his valuation of H?
he was also measuring Type II cepheids which are much dimmer. This distinction had not been discovered yet though
What do all type 1a supernovae have in common?
They have the same luminosity
What is peculiar velocity?
it is the velocity that results in the ordinary classical doppler shift due to the unique motions of a given galaxy
It is distinct from the Hubble effect of expansion
Where do peculiar velocities become problematic?
When they begin to negate the cosmological redshift in the nearby galaxies
What does the cosmological redshift imply
that the universe is expanding everywhere
What is the issue with Einstein’s initial theory of gravity?
If it were true, it would mean that the universe would collapse on itself in the amount of time that it takes for light to traverse the universe
How does Einstein adjust his formula so that the universe does not collapse in on itself?
he uses the cosmological constant
What is the cosmological constant
It balances the attractive force of gravity and the repulsive force of dark energy
What is the repulsive force on other celestial objects?
dark energy
What was the issue of the cosmological constant?
The model was unstable, and slight expansions or contractions in the size of the universe could throw it all off
What fixes the issue of the cosmological constant?
Hubble’s theory of an expanding universe
What is the cosmological principle?
The theory that the universe is both homogenous and isotropic when viewed from a large scale
What is the Hubble Law?
The idea that when the universe expands, the distances between things will proportionally increase
What is Hubble Time?
An estimate of the age of the universe
What is the relationship between Hubble time and expansion speed?
the greater the expansion speed, the smaller the Huibble time
How constant is the Hubble Constant?
it has changed over time so not entirely constant
What is Hubble Length?
an approximate size of the observable universe (and only the observable universe
What does relativity say happens when there is a change in lengths
There is also a change in time
