Unit 1 - Observational Astronomy Flashcards
(45 cards)
What is an astronomical unit?
the distance between the earth and the sun
How far is 1 parsec?
3.26 light years
What are the 2 perpendicular components of light (and all EM radiation)?
an oscillating electric field
an oscillating magnetic field
What wavelengths of radiation are absorbed and scattered the most by clouds / dust?
gamma rays and x-rays
shorter wavelengths scattered the most
What is a black body?
an astronomical body that when cool absorbs all the incoming radiation of all wavelengths and when hot emits radiation with 100% efficiency
What is the relationship between the peak wavelength (colour) emitted and temperature of the black body?
as peak wavelength increases temperature decreases (inversely proportional)
What is the relationship between power of radiation emitted and temperature?
power is directly proportional to T^4
Why are planets not black bodies?
they generate little radiative energy and instead reflect sunlight so the observed colour of a planet doesn’t give a true picture of temperature or power output
Where are electrons found in the atom?
energy levels
the energy level closest to the nucleus is known as the ground state and has the smallest energy value
What happens when electrons absorb a photon of light?
they ‘jump’ to a higher energy level as long as the photon corresponds to a specific energy gap
What happens when an electron emits a photon of light?
it drops down an energy level and releases a photon of light corresponding to the specific energy gap (colour)
What do the emission and absorption spectrum allow us to identify?
identify the elements present within a star or galaxy since each element has a unique spectrum which can be matched up
What is the Doppler Effect?
when radiation emitted by astronomical bodies is effected by the relative speed at which the object travels
Explain the Doppler Effect
a source approaching the observer will have a shorter wavelength and higher frequency
a source moving away from the observer will have a longer wavelength and lower frequency
What significance is the + / - before the v in the Doppler Effect equation?
+v means distance is increasing, source is moving away
-v means distance is decreasing, source is moving closer
What is redshift?
a shift in the spectral lines when all lines move to the right (red end of the spectrum) seen for objects moving away from the source
What are the 3 main functions of telescopes?
1) maximise image brightness (light gathering)
2) resolve images that are separated by small angles
3) magnify distant objects
What is the relationship between aperture and light gathered?
the larger the aperture the more light is gathered
What else does the aperture size of a telescope determine?
the resolving power of the telescope
larger aperture = higher resolving power = smaller angle resolution
What does light diffracted by a circular aperture produce?
a bright disk (Airy disk) with circular fringes
What does Rayleigh’s Criterion state?
2 sources of light are said to be resolved if their Airy disks can be distinguished from each other
What are the 2 different types of telescopes?
refractor telescopes - lenses
reflector telescopes - mirrors
What is chromatic aberration in refractor telescopes?
lenses refract different wavelengths by different amounts, the focal length increases with wavelength, the lens therefore focuses the light of different wavelengths in different positions
What is spherical aberration in reflector telescopes?
when you move away from the centre of the mirror the image becomes blurred because the focal length of the mirror decreases
