# Astronomy Instrumentation Astronomy Summer School for West Africa Daniel Okoh.

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Astronomy Instrumentation Astronomy Summer School for West Africa Daniel Okoh

Astronomy Instrumentation Outline: 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 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

Astronomy Instrumentation Telescopes 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 θ1θ1 θ2θ2

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 θ θ 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 A d D A = D/d * 57.3 degrees

Astronomy Instrumentation Activity 2: Angular size of the Sun A 1.4*10 6 km A = ?? 1.5*10 8 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 = 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 Steering in Azimuth And Elevation Where we have to look to see stars and other objects A.0 B. 10 C. 45 D. 90

Astronomy Instrumentation Steering in Azimuth And Elevation A.0 B. 10 C. 45 D. 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 105 Department of Physics & Astronomy University of Nigeria Nsukka Enugu State Nigeria

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?

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