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Observational Astronomy > Final > Flashcards

Final Flashcards

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0
Q

Reflection nebula

A

Light reflects off interstellar dust grain
Bluish color
Pleiades

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1
Q

Open clusters

A 
100-500 stars 
Found in disk of galaxy
Fairly young 
Beehive cluster m44
Pleiades 
Hyrades
Wild duck cluster m11
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2
Q

Planetary nebula

A

Outer envelope is ejected into space, exposing core (white dwarf)
Ring nebula m57
Owl nebula m97

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3
Q

Emission nebula

A 
Excited, glowing hydrogen gas
Reddish color
Brand new
Rosette nebulae 
Orion Nebula 
Lagoon
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4
Q

Spiral galaxy

A

Gas and dust
Orbits with a plane
Young O&B stars
Open and globular

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5
Q

Elliptical galaxy

A

Very little gas and dust
Random orbits
Old stars

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6
Q

Dark nebula

A

Dust is thick enough to block light
Black color
Trifid nebula
Horse head nebula

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7
Q

Ecliptic

A

Apparent path of the sun through the sky

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8
Q

Cardinal points

A

North
South
East
West

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9
Q

Zenith

A

Point right above observer

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10
Q

Meridian

A

Line that runs from north to South and passes through the zenith

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11
Q

Right ascension

A

East of the vernal equinox. 0-24 hours

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12
Q

Declination

A

Angle N or S of the celestial equator
Ex: Sirius -19 degrees
57 degrees (commerce 180-90-33.2) - 19 = 38 degrees latitude

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13
Q

Precession

A

The tilt of the earths axis changes

23.5 degrees

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14
Q

Altitude and azimuth

A

N 0 degrees
E 90 degrees
S 180 degrees
W 270 degrees

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15
Q

Latitude

A

North or South of the equator

0-90 degrees N or 0-90 degrees south

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16
Q

Longitude

A

East or west of the prime meridian (Greenwich)
0-180 degrees west
0-180 degrees east

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17
Q

Commerce latitude and longitude

A

33.2 N

95 W

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18
Q

Altitude

A

Height of an object above the horizon

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19
Q

Circumpolar stars

A

Stars that never rise nor set. They circle NCP or SCP

From commerce stars with a declination > 57 will be circumpolar

Circumpolar = 90 - latitude of place

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20
Q

Solar time

A

24 hours
When sun is at same point as it was the day before
Isn’t constant cos earth is on an elliptical orbit

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21
Q

Equation of time

A

Corrects for the fact that every day is not 24 hrs due to earths elliptical orbit and tilt of it’s axis

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22
Q

Sidereal time

A 
Measures a day by the position of the stars 
Time measured by the stars 
24 hrs
In solar time it's 23 hr 56 min
Right ascension of the meridian
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23
Q

When are stars best viewed?

A

When they are opposite of the sun

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24
Julian date
January 1, 4713 BC
25
Hour angle
How far an object is east or west of the meridian Positive before meridian (west) Negative after meridian (east)
26
Magnitudes
Hipparchus choose one to measure all the others against (vega)
27
Apparent magnitude (m)
2.512 To find difference in apparent magnitude brightness do 2.512 to the power of the difference in m. Ex: star a: m=7.2 , star b: m=4.1 2.512^(7.2-4.1) = 17.4 times brighter
28
Absolute magnitude (M)
At 10 pc 1 pc = 3.26 lyrs Sun = 4.7 M
29
Spectral type
O B A F G K M hot Cool Blue Red B - V < 0 B - V > .7 Sun = G2V
30
B - V < 0
Blue star
31
B - V > .7
Red star
32
Sun B - V =
.68
33
Telescope
Want a big mirror to let in as much light as possible Needs to be a parabola shaped mirror Measured by diameter
34
Angular resolution
Sin0=1.22(wavelength/diameter) Must be same units
35
500 nm in meters
500x10^-9 m
36
Inches to meters
Times inches by .0254
37
Convert m to arcseconds
Times m by 60 times 60
38
Acrseconds to degrees
Divide it by 3600
39
Focal ratio
10" = F/8 Focal length = 8 x 10 = 80"
40
Focal length
Focal ratio x 10
41
Mag initiation
Focal length / focal length of eyepiece Both in mm Lower mag have wider field of view. Easier to find stuff with.
42
Inches to mm
Times inches by 25.4
43
Field of view
Time it takes for a star to go across eyepiece in seconds | Then divide seconds by 4 to get in arcseconds
44
5000 angstroms in meters
5.0 x 10^-7 m
45
Visual limiting magnitude
2.7 + 5logd (in mm)
46
Max altitude
(180-Latitude-90) + declination
47
Which coordinate is equal for 2 stars that are crossing the meridian at exactly the same time?
Right ascension
48
How to find out what time a star will ride a certain amount of days later
(Days later)(4) | Take that and minus it from the initial time
49
When is right ascension 0?
Vernal equinox | March 22
50
Globular clusters
``` Halo of galaxy 100,000-1,000,000 stars M13 Hercules cluster M22 M3 M5 ```
51
Good seeing
Is really crisp and stars aren't jumping or twinkling because of the atmosphere. With good seeing stars get smaller. At half maximum the radius gets smaller
52
FWHM
Full width half maximum At half maximum the radius of a star gets smaller A stars seeing
53
Air mass (x)
The amount of air you are looking through to see the star. Length of the line. Minimum airmass is 1 Cos z = 1/x X = 1/cos z = sec z is z < 60 degrees X = sec z [1-.0012(sec^2 z -1)] if z > 60
54
Seeing (s)
S = s(at zenith)x^(3/5) Measure of a stars FWHM
55
Reddening
Change of the colour of stars at higher air mass
56
Extinction
Dimming of stars at higher air mass
57
Light detectors
Eye Photographs CCD's
58
Eye
Cones - color (rgb) Rods - low light (black and white). Shapes. When light hits, chemical reaction, receptors pick it up. In lowlight we lose sense of color Concentration of cones at center of eye. It's a logarithmic detector
59
Photographs
Chemical reaction to light coming in Black and white Logarithmic detectors Silver bromide Goes to developer then the fixer Two negatives make a positive
60
CCD
Charged coupled device Linear Each square is a Photoelectric detector (it is an array of photoelectric detectors) Made of silicon Count electrons Sensitive to low light. Bright light saturates it
61
Pixel scale
How many "/pixel your telescope is to know how big an object will be on the pictures (how many pixels it will take to show it) 16" at observatory = .424"/pixel 5" refractor = 2.78"/pixel Ex: Venus is 45" across. So 45"/.424". So it would be about 100 pixels
62
Correcting for background charge
Calibration: Bias image Dark image Flat field images
63
Bias image
To get rid of background charge. Image with 0 expose time. It's just the background image then you subtract it from regular images
64
Dark image
Correct for dark current | Image of the same length of the light image but the shutter is never opened
65
Flat field images
Corrects for no uniformities across the chip like dust Images of a uniformly lit screen or of the twilight sky. Most important
66
Averted vision
Look to the side of a faint object and look at it from peripheral vision
67
Light frames
Actual image
68
Order of calibrating
Bias Flat field Dark frames Light frames
69
Disadvantages of CCDs
Not much dynamic range (fixed by taking multiple exposers then adding them together
70
Advantages of CCDs
Linearity Ease of receiving a picture instantly Sensitivity
71
Ecliptic
The apparent path of the sun through the sky
72
Field of view definition
The amount of sky that can be seen through an eyepiece. Different for every eyepiece.
73
Nanometer
Unit of wavelength | 1x10^9 m
74
Limiting magnitude def
Size of telescope
75
Angular resolution def
The sharpness an object can be seen at. Sin0 = 1.22(wavelength/diameter)
76
Hour angle fed
Position of an object either west or east of the meridian. West is positive. East is negative

Observational Astronomy (1 decks)

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