Astronomy Summer School for West Africa
Astronomy
Instrumentation
Daniel Okoh
Outline:
Telescopes
Telescopes
Telescopes
Astronomy Instrumentation
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
Objective
Eye 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 =
λ
D
Astronomy Instrumentation
Telescopes in Space
Windows and Walls
Telescopes in Space
Astronomy Instrumentation
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
tan θ = x/y
θ
θ
x
y
x
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
A = D/d * 57.3 degrees
A
d
D
Astronomy Instrumentation
Activity 2: Angular size of the Sun
1.4*106
km
A = ??
A
1.5*108 km
Astronomy Instrumentation
Activity 2: Angular size of the Moon
3,475
km
A = ??
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 =
λ
D
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
A.
B.
C.
D.
0
10
45
90
Where we have
to look to see
stars and other
objects
Astronomy Instrumentation
Steering in Azimuth And Elevation
A.
B.
C.
D.
0
10
45
90
Astronomy Instrumentation
Radio Telescope Receivers
Similar in many ways to other receivers we use for
TV and other radio collections
God Dependent
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
Cryogenic
There is need to cool the receivers to really
low temperatures
Astronomy Instrumentation
The Address of stars:
Room 105
Department of Physics & Astronomy
University of Nigeria
Nsukka
Enugu State
Nigeria
Right Ascension
Declination
Celestial Equator
Astronomy Instrumentation
Activity 4: Telescope Pointing
• Determine 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?