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Observational Astronomy > Final > Flashcards

Final Flashcards

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
Q

Julian date

A

January 1, 4713 BC

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25
Q

Hour angle

A

How far an object is east or west of the meridian
Positive before meridian (west)
Negative after meridian (east)

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26
Q

Magnitudes

A

Hipparchus choose one to measure all the others against (vega)

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27
Q

Apparent magnitude (m)

A

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

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28
Q

Absolute magnitude (M)

A

At 10 pc
1 pc = 3.26 lyrs
Sun = 4.7 M

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29
Q

Spectral type

A

O B A F G K M
hot Cool
Blue Red
B - V < 0 B - V > .7

Sun = G2V

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30
Q

B - V < 0

A

Blue star

31
Q

B - V > .7

A

Red star

32
Q

Sun B - V =

A

.68

33
Q

Telescope

A

Want a big mirror to let in as much light as possible
Needs to be a parabola shaped mirror

Measured by diameter

34
Q

Angular resolution

A

Sin0=1.22(wavelength/diameter)

Must be same units

35
Q

500 nm in meters

A

500x10^-9 m

36
Q

Inches to meters

A

Times inches by .0254

37
Q

Convert m to arcseconds

A

Times m by 60 times 60

38
Q

Acrseconds to degrees

A

Divide it by 3600

39
Q

Focal ratio

A

10” = F/8

Focal length = 8 x 10 = 80”

40
Q

Focal length

A

Focal ratio x 10

41
Q

Mag initiation

A

Focal length / focal length of eyepiece

Both in mm

Lower mag have wider field of view. Easier to find stuff with.

42
Q

Inches to mm

A

Times inches by 25.4

43
Q

Field of view

A

Time it takes for a star to go across eyepiece in seconds

Then divide seconds by 4 to get in arcseconds

44
Q

5000 angstroms in meters

A

5.0 x 10^-7 m

45
Q

Visual limiting magnitude

A

2.7 + 5logd (in mm)

46
Q

Max altitude

A

(180-Latitude-90) + declination

47
Q

Which coordinate is equal for 2 stars that are crossing the meridian at exactly the same time?

A

Right ascension

48
Q

How to find out what time a star will ride a certain amount of days later

A

(Days later)(4)

Take that and minus it from the initial time

49
Q

When is right ascension 0?

A

Vernal equinox

March 22

50
Q

Globular clusters

A 
Halo of galaxy
100,000-1,000,000 stars
M13 Hercules cluster
M22 
M3
M5
51
Q

Good seeing

A

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
Q

FWHM

A

Full width half maximum

At half maximum the radius of a star gets smaller

A stars seeing

53
Q

Air mass (x)

A

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
Q

Seeing (s)

A

S = s(at zenith)x^(3/5)

Measure of a stars FWHM

55
Q

Reddening

A

Change of the colour of stars at higher air mass

56
Q

Extinction

A

Dimming of stars at higher air mass

57
Q

Light detectors

A

Eye
Photographs
CCD’s

58
Q

Eye

A

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
Q

Photographs

A

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
Q

CCD

A

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
Q

Pixel scale

A

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
Q

Correcting for background charge

A

Calibration:

Bias image
Dark image
Flat field images

63
Q

Bias image

A

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
Q

Dark image

A

Correct for dark current

Image of the same length of the light image but the shutter is never opened

65
Q

Flat field images

A

Corrects for no uniformities across the chip like dust
Images of a uniformly lit screen or of the twilight sky.
Most important

66
Q

Averted vision

A

Look to the side of a faint object and look at it from peripheral vision

67
Q

Light frames

A

Actual image

68
Q

Order of calibrating

A

Bias
Flat field
Dark frames
Light frames

69
Q

Disadvantages of CCDs

A

Not much dynamic range (fixed by taking multiple exposers then adding them together

70
Q

Advantages of CCDs

A

Linearity
Ease of receiving a picture instantly
Sensitivity

71
Q

Ecliptic

A

The apparent path of the sun through the sky

72
Q

Field of view definition

A

The amount of sky that can be seen through an eyepiece. Different for every eyepiece.

73
Q

Nanometer

A

Unit of wavelength

1x10^9 m

74
Q

Limiting magnitude def

A

Size of telescope

75
Q

Angular resolution def

A

The sharpness an object can be seen at. Sin0 = 1.22(wavelength/diameter)

76
Q

Hour angle fed

A

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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