Observational tools
Universe Now Observational tools
History
• Astronomy – the Oldest science?
• Human eye until the beginning of the 17th century
• Telescope
• Photography at the end of the 19th century
• New observational tools in the 20th century, photometers and radio-telescopes
• 1960s, satellites, computers
Atmosphere
• Filters part of the electromagnetic radiation
• To the Earth’s surface – Optical window 400 – 800 nm – Radio window 1mm – 15 m
• Disturbances – Refraction (light bends in the atmosphere) – Scintillation (stars “twinkle”) – Seeing (stars do not appear point-like) Refraction: Light coming from the Moon gets refracted in the atmosphere and distorts Moon’s image
Observational tools
• Optical telescopes – Observations of visible light
• Radio and sub-millimeter telescopes – Observations of the radio region (radio window)
• Satellites and probes – Other parts of the electromagnetic radiation – Planet, asteroid and comet probes Optical telescopes
• Refracting telescopes – Lenses
• Reflecting telescopes – Mirrors
• In both cases, the most relevant thing is how much light the telescope collects – the diameter of the main lens/mirror Refracting telescope
• A lense acts as the objective, front side of the telescope
• First refracting telescopes at the start of the 17th century – chromatic aberration, focal points for different wavelengths don’t connect • correction: achromatic lenses
• Structural problem: supporting the lense – Largest diameter 102 cm – With large lenses, the focal length of the telescope also becomes large and the telescope has to be very long
• Astrographs: size of the image field 5o – mapping of large areas
Reflecting telescope
• A paraboloid mirror (main mirror) covered with a thin aluminum layer collects the light
• Main mirror reflects the light back to the incident direction – Image at the focal point (prime focus) • Difficult to reach – Usually a secondary mirror that has been placed before the prime focus -> directs light somewhere else • Image at the secondary focus • The shape and position of the secondary mirror defines the focus type • Coma error
Prime focus
• Location where the reflected light forms an image
• Observations difficult because focus is in front of the main mirror
• Placement of large equipment difficult Newton focus
• Secondary mirror – plane mirror – at 45° angle – reflects light out coming from the main mirror outside of the telescope
• pros: no prime focus
• cons: difficult to reach, placement of equipment • Secondary mirror – surface hyperboloid – light reflects out from the hole in the middle of the main mirror
• pros: focus easy to reach
• cons: support structures must be strong enough Coude focus
• Secondary mirror – Structure same as Cassegrain focus – New mirrors that reflect the light out parallel to the axes, light directed at the wanted location
• Pros: Observational tools can be placed to a permanent position
• Cons: light lost in reflections
Equatorial mount
• To direct the telescope, two axes are needed
• Equatorial mount 1. First axis parallel to the rotation axis of the Earth 2. Second axis parallel to the equator
• Pros: Easy to follow a target, rotate one axis
• Cons: Heavy structures (expensive!), mounting depends on your location
Azimuthal mount
• Azimuthal mount 1. First axis is vertical 2. Second axis is horizontal (azimuth)
• Pros: No massive support structures, mounting always the same
• Cons: Target followed by rotating both axes, image field must be rotated, all with a right speed, done by a computer
• 1975 first big telescope (BTA telescope at Caucasus)
Detectors
• Photographic disk
• CCD camera
• Photometers, polarimeters
• Spectrographs SBIG STL-1000M, with 11 million pixels New techniques
• Detectors close to the theoretical 100% limit
• New techniques studied – mosaic structure – active/adaptive optics – multiple mirror structure – interferometer – multiple telescopes – space telescopes
Radio telescopes
• Radio astronomy was born in 1930
• Structure same as in optical telescopes
• Antenna lines – bad resolution of a single telescope – better resolution with antenna lines Metsähovi radio telescope. Figure: Jan Wagner ALMA. Figure: ESO Largest optical telescopes - active Diameter (m) Name Completed Location 10,4 GranTeCan 2007 (2009) La Palma, Canary Islands 10 Keck 1 1992 Mauna Kea, Hawaii 10 Keck 2 1996 Mauna Kea, Hawaii 9,2 Salt 2005 Sutherland, South Africa 9,2 Hobby-Eberle 1997 Mt. Fowlkes, Texas 8,4 LBT 1 2005 Mt. Graham, Arizona 8,4 LBT 2 2006 Mt. Graham, Arizona 8,3 Subaru 1999 Mauna Kea, Hawaii 8,2 Antu (VLT 1) 1998 Cerro Paranal, Chile 8,2 Kuyen (VLT2) 1999 Cerro Paranal, Chile 8,2 Melipal (VLT 3) 2000 Cerro Paranal, Chile 8,2 Yepun (VLT 4) 2000 Cerro Paranal, Chile
Largest optical telescopes – planned
Diameter (m) Name Will be Location completed
100 OWL ? Project cancelled
50 Euro50 ? La Palma or Chile
39,3 ELT 2025 Cerro Armazones
42 LAMA ? Chile? (cancelled?)
30-50 MAXAT ? ? (cancelled?)
30 TMT 2027 Mauna Kea
25 CCAT 2021 Cerro Chajnantor
21,4 (7x8,4) GMT 2029 Las Campanas, Chile
8 LSST 2019–2020 Cerro Pachon, Chile Large radio telescopes
Diameter (m) Name Completed Location 576 Ratan 600 1974 Caucasus, Russia 305 Arecibo 1963 Puerto Rico, USA 100 x 110 Green Bank 2001 Green Bank, USA 100 Effelsberg 1973 Bonn, Germany 76 Jodrell Bank 1957 Macclesfield, UK 70 Jevpatoria 1979 Jevpatoria, Crimea, Ukraine 70 (64) Tidbinbilla 1976 (1987) Tidbinbilla, Australia (ACT) 70 (64?) Goldstone 1958(?) Mojave, California, USA 64 Parkes 1961 Parkes, Australia (NSW) Ideal locations for observatories
• Dark sky – far away from city lights
• High altitude – less atmospheric extinction, above the clouds
• Low humidity
• Infrastructure
• For example: – Andes – Canary islands – Hawaii Funny abbreviations
• NOT = Nordic Optical Telescope – British: Not so large telescope
• VLT = Very Large Telescope
• ELT = Extremely Large Telescope
• OWL = OverWhelmingly Large Telescope Wavelengths Gamma region
• Wavelength shorter than 10-11 m
• First observations at the end of 1960s – OSO 3 observed gamma radiation of the Milky Way
• Observational targets – Pulsars – Gamma Ray bursts (GRBs) Wavelengths X-ray
• Wavelength 0.01 – 10 nm – hard zone 0.01 – 0.1 nm – soft 0.1 – 10 nm
• First observation 1962 – mapping from 1970s (HEAO1 and 2) – now Chandra and XMM-Newton
• Observational targets – Compact stars – Solar flares Wavelengths UV • Wavelength 10 – 400 nm – EUV 10 – 91.2 nm
• Sun UV radiation in 1946 – satellites starting from 1962
• Observational targets – comets – interstellar matter – star surface layers Wavelengths Visible • Wavelength 400 – 700 nm
• Observational tools – naked eye – telescopes – detectors
• Still by far the most common form of astronomical observations! Wavelengths Infrared • Wavelength 700 nm – 1mm – Near-infrared, wavelength less than 5 μmm – Sub-millimeter region, wavelength 0.1 – 1 mm
• Observations carried out from the ground and space
• Observational target – interstellar dust – stars Wavelengths Radio
• Wavelength over 1 mm
• First observations of the radio radiation of space in 1932 (Karl Jansky)
• Significant wavelengths – Hydrogen 21 cm line – Carbon monoxide (CO), multiple lines at 1-3 mm regions
• Observational target – Molecular clouds – Pulsars – Cosmic Microwave Background (CMB) Other forms of radiation
• Cosmic rays – energetic particles – mostly protons and alpha particles – originates mostly from supernovae and the solar wind
• Neutrinos – weakly interacting particles – mass? – observed from the Sun and SN1987A
• Gravitational radiation – masses in an accelerated motion – observable from mergers of black holes and neutron stars Gravitational waves
• Albert Einstein’s theory of General Relativity predicts that gravitation is transported as waves in space-time – gravitational waves
• Observed with LIGO and Virgo – First observation in 2015 – Now 11 confirmed detections of merging black holes or neutron stars
• Measurement of travel time for laser beam shows the stretching of space as a gravitational wave passes by
Other telescopes Nordic Optical Telescope NOT Nordic Optical Telescope
• Located at 2.4 km altitude on Roque de los Muchachos, La Palma, The Canary islands
• 2,5 meter main mirror made in Turku – one of the best main mirrors in quality
• started observations 1989 Nordic Optical Telescope
• Applications for an observational period two times a year (1.10. – 31.3.) and (1.4. – 30.9.)
• In high demand – 1,8 times more observational nights applied for than offered – Used to be 2,3
• Referenced papers 60 – 70 in a year
Hubble space telescope
• Mirror diameter 2,4 m
• Was planned to be launched in October 1986 – Destruction of the Challenger shuttle delayed the launch
• Discovery-shuttle took Hubble into space in 1990
• Technical error in the mirror – aberration – mirror refined wrong – ”correction glass” in 1993
• 4 maintenance missions
Instruments
• ACS camera (Advanced Camera for Surveys, broke in 2007) – New instrument (installed in 2002), replaced the FOC-camera
• NICMOS (Near Infrared Camera and Multi-Object Spectrometer) – Targets covered by dust clouds
• STIS (ST Imaging Spectrograph, broke in 2004) – Studied chemical compositions, temperatures, motions
• WFPC2 (Wide Field and Planetary Camera 2) – 48 filters allow the usage of different wavelengths
• FGS (Fine Guidance Sensors) – Used to move the telescope • ALMA – Atacama Large Millimeter Array
”radio telescope forest” ALMA
• Array of 66 radio telescopes in the Atacama desert in Chile – Interferometry – better resolution can be achieved when using multiple telescopes
• Built to 5 km altitude
• Telescopes transported with trucks
ALMA – Technical information
• System consists of 50 12-meter radio telescopes – Total of 66 telescopes
• Baseline can range from 150 m to 15 km – In interferometry the baseline (longest distance between telescopes) sets the resolution which can be achieved
• Wavelength range 0,3 – 10 mm
• International project: ESO, Japan and USA
• Completed in 2013, operational 2011 Scientific goals
• Study of the Solar System – comets, asteroids
• Star formation in gas clouds
• Clouds around old stars, supernova remnants
• Chemistry and dynamics of gas and molecular clouds
• Formation of galaxies in the early Universe
Pan-STARRS - the Panoramic Survey Telescope & Rapid Response System
• System consists of four 1.8m telescopes
• Corresponds to a 3.6m telescope
• Location Mauna Kea, Hawaii Scientific goals
• Solar System – asteroids – comets
• Outside the Solar System – variable stars – stars being born – microlenses GMT – Giant Magellan Telescope
• Multiple mirror telescope – One central mirror – Six off-axis mirrors
• Diameter of one mirror 8.4m – total area 21.4 m – diameter 24.5 m
• American project with Australia, Brazil and South Korea, located in Chile
• Estimated to start observing in 2029
The Thirty Meter Telescope TMT
• Canadian-american project
• Mirror diameter 30m – 492 pieces of 1,45m mosaic – alt-azimuthal mount
• Plans completed 2008
• Constructions started in 2014
• First light in 2027 (???) Constructions stopped ! TMT and research
• The formation of the first stars – Ending of the dark age after the big bang
• Study of galaxies and large scale structures in the early universe (large distances)
• Formation and evolution of exoplanets – Study of protoplanetary disks – Search for Earth like planets
• Solar System: Kuiper Belt Objects TMT problems
• Is being built on top of Mauna Kea – A sacred land for the local people
• Protests lead to the cancellation of constructions
• Uncertainty of completing the constructions – Telescope moved elsewhere?
(European) Extremely Large Telescope
ELT ELT – Europe’s next generation telescope
• Project of ESO (European Southern Observatory) – Finland takes part
• Mirror diameter 39.3m – 1000 segments, diameter 1.4 m
• Location Cerro Armazones, Chile
• Completed in 2025
• Final decision in 2012 ELT: Scientific goals
• Search and study of exoplanets
• Study of natural units
• First generation of stars
• Study of galaxy formation
• Black holes
• Study related to dark matter and energy
OverWhelmingly Large Telescope
Project cancelled OWL
• Main mirror – diameter 100 m • scientific operations start when the diameter is 60m • area that gathers the light: 6000 m2 – mosaics 3048 pieces, diameter 1,6 m
• Secondary mirror diameter 25,6 m – 216 mosaics
OWL – Technical information
• Wavelengths 320 – 12 000 nm – infrared wavelengths needed
• Requires good observatinal conditions – Location open
• Costs 1200 M€
Project cancelled
Satellites - existing and future ones
James Webb space telescope James Webb space telescope
• Named after the late NASA leader James E. Webb
• Mirror size 6,5 meters
• Launch scheduled to 2021
• Placed to L2 Lagrange-point
James Webb space telescope -instruments
• Mid-infrared instrument MIRI – wavelength range 5 – 27 micrometers
• Near-infrared camera NIRCam – wavelength range 0,6 – 5 micrometers
• Near-infrared spectrograph NIRSpec – average resolution: wavelength range 1 – 5 micrometers – low resolution: wavelength range 0,6 – 5 micrometers James Webb space telescope – Scientific goals
• Ending of the dark age – first stars, reionization
• Galaxies and galaxy evolution
• Formation of stars and protoplanetary disks
• Planetary systems and life Planck
• ESA project
• Launch in 2009
• Main instrument 1.5m mirror telescope
• Studies the Cosmic Microwave Background at 0.3mm – 1 cm
• Duration of flight 15 months First
(Far Infrared and Submillimetre Telescope, now The Herschel Space Observatory)
• Launched together with Planck • Studies the first star generation and galaxy formation and evolution • Placed to L2-point • Mirror size 3.5 m Corot
• Launched in 2006
• Estimated duration 2,5 years
• French project with a few European countries and Brazil
• Mirror diameter 27 cm
• Main mission was to study stellar oscillations (asteroseismology) and find new exoplanets
Kepler
• Launched 6.3.2009
• Telescope – diameter 1,4 meters – receiver 95 megapixel camera (42 x 2k x 1k)
• Observations based on eclipses – planet blocks a small part of the light of its parent star
• Most successful exoplanet mission to date – discovered over 2600 confirmed exoplanets, until the mission ended in Oct 2018 – Kepler’s successor TESS was launched in Apr 2018, has already begun discovering new exoplanets
Gaia
• Global Astrometric Interferometer for Astrophysics
• Observes billion stars (almost 1% of Milky Way’s stars) – During five years it observes each target star one hundred times – Obtains distance, trajectory and brightness variations – Enables more accurate mapping of our galaxy
• Finds also new variable stars, supernovae, asteroids, exoplanets, quasars Gaia
• Building contract 11.5.2006 – costs 317 M€
• Launch in 2012
• Placed to L2-point at 1,5 million km distance
• Resolution: would see a finger nail on the Earth from the Moon’s surface