Topic 1: Observational Astronomy Flashcards
What is the astronomical unit?
Is is the average distance between the earth and the sun. It has a value of 1.5x10^11m
What is parallax?
Where objects close to the earth move faster compared to objects further away.
What does it mean if a star has a large parallx angle?
What does it mean if a star has a small parallax angle?
The star is close to us.
The star is far away from us.
What is a parsec?
An object one parsec away will have a parallax angle of one arcsecond (1”)
With regards to parallax, what is 1 degree equal to?
*Arc
1 degree is equal to 60” (arcminutes)
Thus it is equal to 3600’ (arcseconds)
What would 1” be equal to?
1”= (1/3600) degrees = 0.00028 degress.
Where should a UV, X-ray or gamma ray telescope be placed?
Above the earths atmosphere.
Where should visible light and radiowave telescopes be placed?
They are usually ground based.
What is a blackbody?
When cool, it will absorb all radiation.
When hot, it was emit radiation.
What does Wiens Law let us calculate?
Lambda=b/T
This lets us calculate the max wavelength of light emitted from an object given it’s temperature.
Colour is related to temperature.
Why are planets NOT blackbodies?
They generate little radiation, however they do reflect sunlight.
What is albedo?
This is the (light reflected from a sphere)/(light incident on it)
What does it mean if a galaxy is redshifted?
It is moving away from the observer.
What does it mean if a galaxy is blueshifted?
It is moving towards the observer.
What does spectroscopy tell us about a star/planet/galaxy?
What elements or molecules it is made up of.
How can the frequency and wavelength doppler equations be equated?
Flip the signs in the square root.
What increases resolving power in a telescope?
Increasing the aperture size.
What does a larger aperture size cause?
Higher resolving power
Finer angular resolution
What are the two main types of telescopes?
Refractive and reflective
What is an issue commonly found with lenses?
Chromatic aberration. This is where light at different wavelengths is refracted by different amounts.
What makes mirrors more advantageous over lenses?
They are not affected by chromatic aberration.
What is angular resolution?
This is the smallest angular seperation two objects can have before they blur together.
What factors affect where a telescope is built?
Atmospheric effects
Light pollution
Cloud cover.
This makes the most optimal place for a telescope a mountain-top.
What is adaptive optics?
This is where a reference beam of light is used to calculate how much a mirror must be deformed to account for atmospheric effects.
What is the relationship between angular resolution and resolving power?
The smaller the angular resolution, the higher the resolving power.
What is the Zenith?
This is the point in the sky directly above the observer
What is a circumpolar star?
A star that doesn’t rise or set. The altitude min “amin” will be =<0
What is the difference between solar time and sidereal time?
Solar time is the earth relative to the sun
Sidereal time is the earth relative to the stars
How many more days are in a sidereal year?
1 more than a solar year.
