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

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Optical Telescopes

They come in various sizes

and form

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Optical Telescopes: Basic Operation

ObjectiveEye piece

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Optical Telescopes: Basic Operation

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Radio Telescopes

They need to be big! Really really big!!

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Why?The Quest for more!

Oliver Twist

θ =

λD

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Telescopes in Space

Windows and Walls

Astronomy InstrumentationTelescopes in Space

Hubble Space Telescope

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Angular sizes in astronomy

θ

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If the same object is farther away, the angular size is

smaller

θ1

θ2

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Objects of different linear sizes can have the same

angular sizes

θ

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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

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Activity 2: Angular size of the Sun

A

1.4*106

kmA = ??

1.5*108 km

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Activity 2: Angular size of the Moon

A

3,475 km

A = ??

384,400 km

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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!?

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Why Radio Telescopes should be larger than optical

telescopes

θ =

λD

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Activity 3: What Radio = Optical telescope ?

A 25 cm Optical Telescope will have same resolution as a …… cm Radio

TelescopeAssume Optical Telescope λ = 500 nm

And Radio Telescope λ = 6 cm

30 km ??

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VLBI (Very Long Baseline Interferometry)

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Radio Antenna Surfaces

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Radio Antenna Surfaces

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Steering in Azimuth And

Elevation

Where we have to look to see stars and other

objects

A. 0B. 10C. 45D. 90

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Steering in Azimuth And Elevation A. 0

B. 10C. 45D. 90

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Radio Telescope Receivers Similar in many ways to other receivers we

use for TV and other radio collectionsMajor difference:

Astronomy signals are really very weak compared to other terrestrial signals

What constitutes noise is therefore highSignal to noise ratios can be reduced

by reducing receiver temperaturesThere is need to cool the receivers to

really low temperatures

God Dependent

Cryogenic

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The Address of stars:

Right Ascension

Declination

Room 105Department of Physics &

AstronomyUniversity of Nigeria

NsukkaEnugu State

Nigeria

Celestial Equator

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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?