Chapter 1: Observing the Night Sky

Question 1

Asterism

Answer 1

• sub grouping of if stars in a larger group, sometimes associated with each other
• sub set of a constellation

Question 2

Stars ranked brightness based on

Answer 2

Their Greek laters (brightest alpha and so fourth)

Question 3

The magnitude system

Answer 3

• Quantitive system of brightness of objects in the night sky
• Negative nums mean mean the brightest objects
• how bright they appear to be

Question 4

Distances

Answer 4

• 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

Question 5

The celestial sphere

Answer 5

• 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

Question 6

Horizon diagram

Answer 6

Captures what the night sky looks like from a point

Question 7

Zenith

Answer 7

Point directly above you on Earth

Question 8

Circumpolar star

Answer 8

Star that from your view can make a full circle, always above our local horizon

Question 9

Nadir

Answer 9

The exact opposite point of zenith

Question 10

Ecliptic

Answer 10

• 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

Question 11

Where the celestial equator crosses the ecliptic

Answer 11

Equinoxes which means equal night

Question 12

Altitude and Azimuth

Answer 12

• 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

Question 13

Right Ascension and Declination

Answer 13

-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

Question 14

Alt-azimuth mounting

Answer 14

Not to good only goes up and down and left and right

Question 15

Equatorial mounting

Answer 15

Follows the axis of the star

Question 16

What causes seasons?

Answer 16

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

Question 17

Aphelion

Answer 17

Farthest from the sun

Question 18

Peri-Helion

Answer 18

When the object is at its closest to the sun

Question 19

Analemma

Answer 19

• the sun has a different ascension and declination based on the time of year
• sun is lower in winter and higher in summer

Question 20

Advantages and Disadvantages to telescopes in space

Answer 20

• 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

Question 21

Optical Telescopes

Answer 21

• Have either lenses or mirrors
• primary is the first thing the photons are hitting (also called objective)
• every other mirror is the secondary

Question 22

Difference between mirrors or lenses

Answer 22

• have concave mirrors or convex lenses
• lenses called refractors
• mirrors called reflectors
• mirrors used more then lenses due to their advantages

Question 23

Focal length

Answer 23

Distance between the lens and the point the light is brought to

Question 24

Chromatic aberration

Answer 24

• 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

Question 25

Field of view

Answer 25

Is the angular extend captured on the sky

Question 26

How characterize telescopes

Answer 26

By their aperture and their f-ratio

Question 27

Plate scale

Answer 27

Since Fo is constant for any given telescope we can define a cameras plate scale as (2 theta/distance on camera)

Question 28

Pixel scale

Answer 28

Relation between angular scale on the sky and number of pixels
Measured in arcsec/pixel

Question 29

Properties of telescopes

Answer 29

Most important property and the telescope size

Number of photons collected in scales d^2

Question 30

Resolution

Answer 30

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

Question 31

Diffraction limit

Answer 31

Telescopes on the ground do not work to their diffraction limit but ones in space can

Question 32

Seeing

Answer 32

When the atmosphere blues an image

Question 33

Seeing disk

Answer 33

Smeared out image of a star

Question 34

Adaptive optics

Answer 34

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

Question 35

Charge couple device

Answer 35

Contain a tiny capacitor in every cell that accumulates charge through photoelectric effect
-measures how many photons come in

Question 36

Where telescopes are placed

Answer 36

• 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)

Question 37

Advantages of radio telescopes

Answer 37

• don’t have to clean
• can observe during the day
• interforemetry: takes incoming photos from two different places and put them together

Question 38

Thirty meter telescope

Answer 38

• 492 segmented mirrors
• can see loonie from Victoria in Calvary
• dome built in Canada

Question 39

Closest star to the sun

Answer 39

Proxima Centauri at 4 to 13 km away