Astrophysics Flashcards
What is the doppler effect?
The apparent change in wavelength of a wave as the source moves relative to the observer. Source moving away(longer wavelength) = Red shift, Source moving towards(shorter wavelength) = Blue shift
What are the 2 methods to detect exoplanets?
Doppler Shift/Radial velocity method and The transit method
What is the scale of the Hipparcos Scale?
- Brightest stars have a apparent magnitude of 1
- Dimmest objects the naked eye can detect have a magnitude of 6
- Intensity of apparent magnitude 1 is 100x intensity of magnitude 6
- Decrease of 1 on scale translates to 2.51x increase in intensity
What is the inverse square law?
Intensity = Power/4πd² , d = distance from the sun in metres
Assume star is spherical and power is being emitted in all directions
What is a black body?
A perfect emitter and absorber of all possible wavelength of radiation
What are the characteristics of all the spectral classes?
O - Blue - 50,000K to 25,000K - He+ and He absorption lines
B - Blue - 25,000K to 11,000K - He and H absorption lines
A - Blue white - 11,000K to 7500K - H and some metal ion absorption lines
F - White - 7500K to 6000K - Metal ion absorption lines
G - Yellow white 6000K to 5000K - Metal ion and metal atom absorption lines
K - Orange - 5000K to 3500K - neutral metal atoms absorption lines
M - Red - <3500K - neutral atoms absorption lines and absorption lines for compounds like TiO
What is the cosmological principle?
On a large scale, the Universe is:
- Homogeneous (Every part is the same as every other part)
- Isotropic (Everything looks the same in every direction, so there is no centre)
What is dark energy?
The rate of expansion of the universe should be decreasing as all the mass in the universe is attracted together by gravity, however the rate of expansion is increasing. Dark energy is a theorised type of energy which fills the whole of space which allows for this
What are Quasars?
Active galactic nuclei - supermassive black holes surrounded by a disc of matter, which cause the quasar to emit radiation from the poles when absorbed. They display very large red shifts, meaning they are very far away and their power output is around that of an entire galaxy.
What is the Raleigh Criterion?
Two objects will not be resolved if any part of the central maximum of either part of the images falls within the first minimum diffraction ring of the other.
What is Stefan’s law?
Power output of a star is directly proportional to its surface area and absolute temperature to the 4th power
What is spherical abberation?
An effect caused by the curvature of a lens or mirror which leads to there being no focal point for the light rays and the image becomes blurry or distorted.
What is Doppler shift/ radial velocity method?
Observation of the host star’s line spectrum. Red shifted when moving away from Earth, blue shifted when moving towards Earth. Suggests star is ‘wobbling’ so there must be an exoplanet exerting a gravitational force on it.
What is the transit method?
Observation of the host star’s light intensity. If an exoplanet crosses in front of it, the intensity decreases. Info on timings and other data can be used to figure out speed and size of exoplanet.
What factor of a telescope leads to a brighter image?
Collecting power
What telescope is affected by chromatic aberration?
Refracting telescopes
What telescope is affected by spherical aberration?
Reflecting and refracting telescopes
What is parallax?
The apparent change of position of a nearer star in comparison to distant stars in the background. Due to Earth’s orbit of the sun.
Define the parsec
The distance at which the angle of parallax is 1 arcsecond(1/3600 degrees).
What is the equation to measure distances of nearby stars?
Distance to the star(pc) = Radius of the Earth’s orbit / angle of parallax(radians)
What is the equation to measure an objects’ distance from Earth?
half the angle subtended(radians) = radius of the object / distance to the object
What is the relationship between collecting power and aperture diameter?
Collecting power of a telescope is proportional to the square of its aperture diameter
What is a “real image”?
An image which can be projected onto a screen
What is a CCD?
A charge coupled device is an array of light sensitive pixels that become charged when exposed to light for a pre-set time
Describe how a CCD works
- CCD is exposed to light for a pre-set time, charging the array of light sensitive pixels
- Charge is transferred to a capacitor, where the voltage across it is read
- Each p.d value is proportional to energy of incident light which is used to create an image
Define quantum efficiency
The proportion of incident photons falling on a light detector that are detected
What is distinguished about the image when the object is further than 2f from the lens?
- Inverted image
- Real image
- Diminished image
What is distinguished about the image when the object is 2f from the lens?
- Inverted image
- Real image
- Same size image
What is distinguished about the image when the object is located between 2f and f from the lens?
- Inverted image
- Real image
- Magnified image
What is distinguished about the image when the object is f from the lens?
- Image formed is at infinity
- No image is formed
What is distinguished about the image when the object is closer than f from the lens?
- Upright image
- Virtual image
- Magnified image
What is normal adjustment?
Where the focus of the objective lens and the focus of the eyepiece lens are at exactly the same point