Final Flashcards
Reflection nebula
Light reflects off interstellar dust grain
Bluish color
Pleiades
Open clusters
100-500 stars Found in disk of galaxy Fairly young Beehive cluster m44 Pleiades Hyrades Wild duck cluster m11
Planetary nebula
Outer envelope is ejected into space, exposing core (white dwarf)
Ring nebula m57
Owl nebula m97
Emission nebula
Excited, glowing hydrogen gas Reddish color Brand new Rosette nebulae Orion Nebula Lagoon
Spiral galaxy
Gas and dust
Orbits with a plane
Young O&B stars
Open and globular
Elliptical galaxy
Very little gas and dust
Random orbits
Old stars
Dark nebula
Dust is thick enough to block light
Black color
Trifid nebula
Horse head nebula
Ecliptic
Apparent path of the sun through the sky
Cardinal points
North
South
East
West
Zenith
Point right above observer
Meridian
Line that runs from north to South and passes through the zenith
Right ascension
East of the vernal equinox. 0-24 hours
Declination
Angle N or S of the celestial equator
Ex: Sirius -19 degrees
57 degrees (commerce 180-90-33.2) - 19 = 38 degrees latitude
Precession
The tilt of the earths axis changes
23.5 degrees
Altitude and azimuth
N 0 degrees
E 90 degrees
S 180 degrees
W 270 degrees
Latitude
North or South of the equator
0-90 degrees N or 0-90 degrees south
Longitude
East or west of the prime meridian (Greenwich)
0-180 degrees west
0-180 degrees east
Commerce latitude and longitude
33.2 N
95 W
Altitude
Height of an object above the horizon
Circumpolar stars
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
Solar time
24 hours
When sun is at same point as it was the day before
Isn’t constant cos earth is on an elliptical orbit
Equation of time
Corrects for the fact that every day is not 24 hrs due to earths elliptical orbit and tilt of it’s axis
Sidereal time
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
When are stars best viewed?
When they are opposite of the sun
Julian date
January 1, 4713 BC
Hour angle
How far an object is east or west of the meridian
Positive before meridian (west)
Negative after meridian (east)
Magnitudes
Hipparchus choose one to measure all the others against (vega)
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
Absolute magnitude (M)
At 10 pc
1 pc = 3.26 lyrs
Sun = 4.7 M
Spectral type
O B A F G K M
hot Cool
Blue Red
B - V < 0 B - V > .7
Sun = G2V
B - V < 0
Blue star
B - V > .7
Red star
Sun B - V =
.68
Telescope
Want a big mirror to let in as much light as possible
Needs to be a parabola shaped mirror
Measured by diameter
Angular resolution
Sin0=1.22(wavelength/diameter)
Must be same units
500 nm in meters
500x10^-9 m
Inches to meters
Times inches by .0254
Convert m to arcseconds
Times m by 60 times 60
Acrseconds to degrees
Divide it by 3600
Focal ratio
10” = F/8
Focal length = 8 x 10 = 80”
Focal length
Focal ratio x 10
Mag initiation
Focal length / focal length of eyepiece
Both in mm
Lower mag have wider field of view. Easier to find stuff with.
Inches to mm
Times inches by 25.4
Field of view
Time it takes for a star to go across eyepiece in seconds
Then divide seconds by 4 to get in arcseconds
5000 angstroms in meters
5.0 x 10^-7 m
Visual limiting magnitude
2.7 + 5logd (in mm)
Max altitude
(180-Latitude-90) + declination
Which coordinate is equal for 2 stars that are crossing the meridian at exactly the same time?
Right ascension
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
When is right ascension 0?
Vernal equinox
March 22
Globular clusters
Halo of galaxy 100,000-1,000,000 stars M13 Hercules cluster M22 M3 M5
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
FWHM
Full width half maximum
At half maximum the radius of a star gets smaller
A stars seeing
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
Seeing (s)
S = s(at zenith)x^(3/5)
Measure of a stars FWHM
Reddening
Change of the colour of stars at higher air mass
Extinction
Dimming of stars at higher air mass
Light detectors
Eye
Photographs
CCD’s
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
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
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
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
Correcting for background charge
Calibration:
Bias image
Dark image
Flat field images
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
Dark image
Correct for dark current
Image of the same length of the light image but the shutter is never opened
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
Averted vision
Look to the side of a faint object and look at it from peripheral vision
Light frames
Actual image
Order of calibrating
Bias
Flat field
Dark frames
Light frames
Disadvantages of CCDs
Not much dynamic range (fixed by taking multiple exposers then adding them together
Advantages of CCDs
Linearity
Ease of receiving a picture instantly
Sensitivity
Ecliptic
The apparent path of the sun through the sky
Field of view definition
The amount of sky that can be seen through an eyepiece. Different for every eyepiece.
Nanometer
Unit of wavelength
1x10^9 m
Limiting magnitude def
Size of telescope
Angular resolution def
The sharpness an object can be seen at. Sin0 = 1.22(wavelength/diameter)
Hour angle fed
Position of an object either west or east of the meridian. West is positive. East is negative
