Chapter 1: Observing the Night Sky Flashcards
Asterism
- sub grouping of if stars in a larger group, sometimes associated with each other
- sub set of a constellation
Stars ranked brightness based on
Their Greek laters (brightest alpha and so fourth)
The magnitude system
- Quantitive system of brightness of objects in the night sky
- Negative nums mean mean the brightest objects
- how bright they appear to be
Distances
- 1 AU = 1.5 times 10 to the 8 km
Used in solar system
-1 light year = 9.5 times 10 to the 12 km
-light year is the distance it takes light to travel in one year used for distances to stars
The celestial sphere
- Everything on the night sky is projected on a sphere
- celestial equator, North celestial pole bard in terrestrial land marks
- the earth rotates which makes the stars look like they are moving
Horizon diagram
Captures what the night sky looks like from a point
Zenith
Point directly above you on Earth
Circumpolar star
Star that from your view can make a full circle, always above our local horizon
Nadir
The exact opposite point of zenith
Ecliptic
- The suns annual apparent motion through the sky
- it is 23.5 degrees above the celestial equator due to the 23.5 degree tilt of the Earth
- The northernmost point of the ecliptic is called the solstice and similarly for the winter solstice is the south
Where the celestial equator crosses the ecliptic
Equinoxes which means equal night
Altitude and Azimuth
- zero point is the observers position
- up-down left right
- advantages: easy
- disadvantages: set to the observers position and not useful for fixed set coordinates
Right Ascension and Declination
-Declination measured in degrees up down
-reference point measured is celestial equator
-max dec +90 and min -90
-ascension measured around celestial equator
-used time from (0-24h) eastward
Advantage: independent of persons position
Alt-azimuth mounting
Not to good only goes up and down and left and right
Equatorial mounting
Follows the axis of the star
What causes seasons?
The angle of the sun causes seasons
- when beams of light hit parallel it is warmer whereas when they are spread out it’s colder
- season are because the earth is tilted 23.5 degrees
Aphelion
Farthest from the sun
Peri-Helion
When the object is at its closest to the sun
Analemma
- the sun has a different ascension and declination based on the time of year
- sun is lower in winter and higher in summer
Advantages and Disadvantages to telescopes in space
- doesn’t deal with turbulence from atmosphere
- can get more waves then just visual and radio
- very expensive
- if something went wrong can’t fix it
Optical Telescopes
- Have either lenses or mirrors
- primary is the first thing the photons are hitting (also called objective)
- every other mirror is the secondary
Difference between mirrors or lenses
- have concave mirrors or convex lenses
- lenses called refractors
- mirrors called reflectors
- mirrors used more then lenses due to their advantages
Focal length
Distance between the lens and the point the light is brought to
Chromatic aberration
- the effect where by the refraction that you get by the lens is wave length dependant
- mirrors are reflectors and are not wave length dependant
Field of view
Is the angular extend captured on the sky
How characterize telescopes
By their aperture and their f-ratio
Plate scale
Since Fo is constant for any given telescope we can define a cameras plate scale as (2 theta/distance on camera)
Pixel scale
Relation between angular scale on the sky and number of pixels
Measured in arcsec/pixel
Properties of telescopes
Most important property and the telescope size
Number of photons collected in scales d^2
Resolution
Spacel scale in which and object can be resolved
-for and mirror or lens size there is a limiting resolution the can be achieved called a diffraction limit
Diffraction limit
Telescopes on the ground do not work to their diffraction limit but ones in space can
Seeing
When the atmosphere blues an image
Seeing disk
Smeared out image of a star
Adaptive optics
Effects of atmosphere can be overcome by AO
- used an adaptive mirror to correct the wave shapes
- uses a guide star to find correctness
- allows telescopes to work at their diffraction limits
Charge couple device
Contain a tiny capacitor in every cell that accumulates charge through photoelectric effect
-measures how many photons come in
Where telescopes are placed
- sky mostly clear
- above clouds on mountain
- dry environment
- no light pollution
- good seeing
Mainly (Hawaii on volcanoes Mauna Kea and Chili in Chilean Atacama desert)
Advantages of radio telescopes
- don’t have to clean
- can observe during the day
- interforemetry: takes incoming photos from two different places and put them together
Thirty meter telescope
- 492 segmented mirrors
- can see loonie from Victoria in Calvary
- dome built in Canada
Closest star to the sun
Proxima Centauri at 4 to 13 km away
