T elescopes T elescopes Ryan Orvedahl Ryan Orvedahl ASTR 1040 - PowerPoint PPT Presentation

T elescopes T elescopes Ryan Orvedahl Ryan Orvedahl ASTR 1040 Rec ASTR 1040 Rec

T oday’s Class - T oday’s Class - T elescopes T elescopes Measuring a telescope’s Measuring a telescope’s performance performance Ways to measure light Ways to measure light Angular resolution Angular resolution Aperture synthesis Aperture synthesis

T elescope Fundamentals T elescope Fundamentals Light is a wave Light is a wave Light is a particle Light is a particle

T elescope Fundamentals T elescope Fundamentals Measures of telescope performance: Measures of telescope performance: Ability to collect and measure light (efgective Ability to collect and measure light (efgective area) area) How big does a point look? (angular How big does a point look? (angular resolution) resolution) Ability to separate wavelengths (spectral Ability to separate wavelengths (spectral resolution) resolution)

Collecting & Measuring Collecting & Measuring Light Light Measuring Measurin Particles g Waves

Angular Resolution Angular Resolution

Angular Resolution Angular Resolution

Angular Resolution Angular Resolution Difgraction Difgraction For a circular aperture: For a circular aperture:

Angular Resolution Angular Resolution What is D D? ? What is

Angular Resolution Angular Resolution Suppose you wanted to take an image (2 Suppose you wanted to take an image (2 pixels by 2 pixels) of Alpha Centauri A, one of pixels by 2 pixels) of Alpha Centauri A, one of our nearest stellar neighbors at 4.3 ly away. our nearest stellar neighbors at 4.3 ly away. Assume that it has a radius of 1.2 R sun and Assume that it has a radius of 1.2 R sun and you want a picture in optical light (l l = 500 = 500 you want a picture in optical light ( nm). How big of a difgraction limited nm). How big of a difgraction limited telescope would you need? telescope would you need? Constants and Constants and Conversions Conversions R sun = 700 Mm R sun = 700 Mm 1 ly = 9.5 x 10 15 m 1 ly = 9.5 x 10 15 m

Angular Resolution Angular Resolution Clicker Question: Now suppose you want both Clicker Question: Now suppose you want both an optical (l l = 500 nm) image of alpha = 500 nm) image of alpha an optical ( Centauri and a radio (l l = 5 mm) image with = 5 mm) image with Centauri and a radio ( the same angular resolution. What how big of the same angular resolution. What how big of a difgraction limited radio telescope would you a difgraction limited radio telescope would you need? need? A. 2.89 mm C. 2.89 km A. 2.89 mm C. 2.89 km B. 2.89 m D. 289 km B. 2.89 m D. 289 km

Angular Resolution Angular Resolution

Aperture Synthesis Aperture Synthesis Interferometers Interferometers Combine signals from Combine signals from difgerent telescopes difgerent telescopes Get the difgraction limit Get the difgraction limit of a telescope as big as of a telescope as big as the distance between the distance between the telescopes the telescopes Requires very careful Requires very careful optics or atomic clocks optics or atomic clocks and fast computers and fast computers

Aperture Synthesis Aperture Synthesis

Aperture Synthesis Aperture Synthesis Atacama Large Millimeter Array (ALMA)

Aperture Synthesis Aperture Synthesis 6 telescopes 6 telescopes

Aperture Synthesis Aperture Synthesis 25 telescopes 25 telescopes

Aperture Synthesis Aperture Synthesis 640 telescopes 640 telescopes

Aperture Synthesis Aperture Synthesis