astronomy instrumentation astronomy summer school for west africa daniel okoh
TRANSCRIPT
Astronomy Instrumentation
Astronomy Summer School for West Africa
Daniel Okoh
Astronomy Instrumentation
Outline:
Telescopes
Telescopes
Telescopes
Astronomy Instrumentation
Telescopes: What are they?They are instruments that enable us ‘see’ distant objects by gathering ‘light’ from them
Astronomy Instrumentation
Telescopes: What are they?
Optical Telescopes Radio Telescopes
Astronomy Instrumentation
Optical Telescopes
They come in various sizes
and form
Astronomy Instrumentation
Optical Telescopes: Basic Operation
ObjectiveEye piece
Astronomy Instrumentation
Optical Telescopes: Basic Operation
Astronomy Instrumentation
Radio Telescopes
They need to be big! Really really big!!
Astronomy Instrumentation
Why?The Quest for more!
Oliver Twist
θ =
λD
Astronomy Instrumentation
Telescopes in Space
Windows and Walls
Astronomy InstrumentationTelescopes in Space
Hubble Space Telescope
Astronomy Instrumentation
Angular sizes in astronomy
θ
Astronomy Instrumentation
If the same object is farther away, the angular size is
smaller
θ1
θ2
Astronomy Instrumentation
Objects of different linear sizes can have the same
angular sizes
θ
Astronomy Instrumentation
Activity 1: Estimate the angular size of your full fist at
arm’s length
Astronomy Instrumentation
Activity 1: Estimate the angular size of your full fist at
arm’s length
Astronomy Instrumentation
Activity 1: Estimate the angular size of your full fist at
arm’s length
θθ y
x
x
tan θ = x/y
2θ = 2 tan-1 (x/y)
Astronomy Instrumentation
Activity 1: Estimate the angular size of your full fist at
arm’s length
Astronomy Instrumentation
Small angle approximation
Ad
DA = D/d * 57.3 degrees
Astronomy Instrumentation
Activity 2: Angular size of the Sun
A
1.4*106
kmA = ??
1.5*108 km
Astronomy Instrumentation
Activity 2: Angular size of the Moon
A
3,475 km
A = ??
384,400 km
Astronomy Instrumentation
0.5 degrees! for both Sun and Moon
Sun and Moon same size?
Eclipse Implication?
Fist or finger to block out the Moon?
Astronomy Instrumentation
Telescope Resolutions
2 degrees!?
Astronomy Instrumentation
Why Radio Telescopes should be larger than optical
telescopes
θ =
λD
Astronomy Instrumentation
Activity 3: What Radio = Optical telescope ?
A 25 cm Optical Telescope will have same resolution as a …… cm Radio
Telescope
Assume Optical Telescope λ = 500 nm And Radio Telescope λ = 6 cm
30 km ??
Astronomy Instrumentation
VLBI (Very Long Baseline Interferometry)
Astronomy Instrumentation
Radio Antenna Surfaces
Astronomy Instrumentation
Radio Antenna Surfaces
Astronomy Instrumentation
Steering in Azimuth And
Elevation
Where we have to look to see stars and other
objects
A. 0B. 10C. 45D. 90
Astronomy Instrumentation
Steering in Azimuth And Elevation A. 0
B. 10C. 45D. 90
Astronomy Instrumentation
Radio Telescope Receivers
Similar in many ways to other receivers we use for TV and other radio collections
Major difference:
Astronomy signals are really very weak compared to other terrestrial signals
What constitutes noise is therefore high
Signal to noise ratios can be reduced by reducing receiver temperatures
There is need to cool the receivers to really low temperatures
God Dependent
Cryogenic
Astronomy Instrumentation
The Address of stars:
Right Ascension
Declination
Room 105Department of Physics &
AstronomyUniversity of Nigeria
NsukkaEnugu State
Nigeria
Celestial Equator
Astronomy Instrumentation
Activity 4: Telescope PointingDetermine the direction (azimuth and elevation) a telescope
should point this evening at 6:34 PM to be able to observe α – Centauri from here in Abuja.
Assume 2 telescopes at Nsukka and Abuja are to be used for VLBI observations of Sirius at 8:22 AM tomorrow morning. At what directions should each of the telescopes point?
Will it be possible to join a telescope at Nanshan, China to this VLBI observation? What about a telescope at Cape Town, South Africa?