Transcript FROM DAGUERREOTYPE TO CCDS – HOW PHOTOGRAPHY CHANGED ASTRONOMY Craig Mackay, Institute of Astronomy, University of Cambridge. 8 February 2013: European AstroFest-2013

FROM DAGUERREOTYPE TO CCDS –
HOW PHOTOGRAPHY CHANGED
ASTRONOMY
Craig Mackay,
Institute of Astronomy, University of Cambridge.
8 February 2013: European AstroFest-2013
Introduction.
• Will discuss why photography produced a step change in
the way astronomy was carried out.
• Will describe the contribution that photography has made.
• Astronomy had a central role in the development of solidstate detectors.
• However still limited by atmospheric turbulence so
astronomers were forced to go into space.
• Will also describe some new techniques that are already
giving pictures with much higher resolution from the
ground than Hubble is giving from space.
8 February 2013: AstroFest-2013
Scientific Studies require data recording.
• Very difficult to do science with drawings as they are all
very personal.
• Visual observations and drawings were all that was
possible from Galileo until 1840 when Daguerre made a
photo of the moon.
• However, photographic plates were (and still are) much
less sensitive than the eye.
• But you had to use them…………………
8 February 2013: AstroFest-2013
14 December 2007: U3A, King’s Lynn
Photographic Plates
• The first astronomical pictures were taken in the mid-19th
century.
• By the end of that century they were being used for very
long exposure images.
• They revealed large numbers of stars in, for example, the
Orion nebula.
• George Eastman of Kodak developed a machine to coat
plates with photographic emulsion which made them
cheaper and of much more consistent quality.
• For over 100 years the photographic plate was to
completely dominate astronomical recording.
8 February 2013: European AstroFest-2013
Photographic Plates
• Not very sensitive, but could cover very large areas.
• Glass plates greatly preferred over film because
dimensionally stable. Film seldom used.
• Colour film almost never used (much less sensitive).
• At best 1-2% efficient (human eye can be up to 20% when
fully dark adapted).
• Plates can integrate for hours (it is claimed), while the
human eye integrates from 5 msecs to 15 secs max.
• Plates can be very uniform: critical for sky limited images.
8 February 2013: European AstroFest-2013
Photographic
Plates
• To this day the only allsky surveys we have are
photographic (digitised
for HST support).
• The 48 inch Palomar
Schmidt telescope gives
very wide field of view,
6.6° x 6.6° or 11 times
the size of the moon.
• These plates are 350 x
350 mm (14 x 14").
• This three colour image
of M 31 is 2° x 3°.
Efficient Electronic Detectors
• Eventually integrated circuit technology came to the rescue
with the Charge-Coupled Detector (CCD).
• Relatively cheap to make, very efficient (up to 98%), all
electronic, robust, matched well to telescope optics.
• Can be used for space missions.
• UK a key leader in the development of scientific CCDs.
8 February 2013: European AstroFest-2013
Efficient Electronic
Detectors
• Can be made into large
mosaics to cover very
wide fields.
• This is a large-scale
survey instrument.
• This one has 1.4 billion
pixels for $5 million.
• Widely used in phones,
cameras, videos, etc.
8 February 2013: European AstroFest-2013
Atmospheric
Turbulence
• Causes images to be
smeared out giving
no more detail than a
small (few inches
diameter) telescope.
• May be corrected for
bright stars.
8 February 2013: European AstroFest-2013
Atmospheric Turbulence
• Can avoid by putting a telescope into space.
• The Hubble Space Telescope (HST) and many others have been
remarkably successful.
• Typically HST
gives 5-8 times
the ground-based
detail.
• Also lets us
work in
wavelengths
(colours) that do
not penetrate the
atmosphere.
8 February 2013: European AstroFest-2013
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
14 December 2007: U3A, King’s Lynn
21 July 2010: The Art of Scientific Imaging
More Detailed Images than Hubble can Give.
• Double star with 14
arc sec separation,
shown side by side.
• The scale is about 4
arc sec vertically
• Images were taken
with 10 millisec frame
time, and stars are
each 6.0 magnitude.
• More detail means a bigger telescope.
• Must be ground-based, but must deal with turbulence in the
atmosphere.
• New technique developed in Cambridge called Lucky Imaging.
8 February 2013: European AstroFest-2013
Lucky Astronomy
• Now and again, the atmosphere sorts itself out, and giving
images as sharp as theoretically possible.
• We take images with a bright reference star in the field fast
enough (10-100 frames/second) to freeze the turbulence.
• Then frames are selected for image sharpness, shifted-andadded to give a diffraction limited image.
• We use a truly noise-free, high-speed CCD camera, using a
detector made by E2V Technologies (Chelmsford, UK) in
a camera we built in Cambridge.
8 February 2013: European AstroFest-2013
LuckyCam on the NOT
8 February 2013: European AstroFest-2013
LuckyCam on the NOT
8 February 2013: European AstroFest-2013
Lucky Imaging: The Einstein Cross
• The image on the left is from the Hubble Space Telescope Advanced Camera for Surveys
(ACS) while the image on the right is the lucky image taken on the NOT in July 2009 through
significant amounts of dust.
• The central slightly fuzzy object is the core of the nearby Zwicky galaxy, ZW 2237+030
that gives four gravitationally lensed images of a distant quasar at redshift of 1.7
8 February 2013: European AstroFest-2013
Extraordinary Results with Lucky Imaging
• The International
Space Station, with
Space Shuttle Atlantis
and a Soyuz
Spacecraft. Taken
with a ground-based
telescope using
Lucky Imaging in
June 2007.
• Resolution was about
20 cm at an altitude
of 330 km altitude, or
~ 0.12 arcsec.
8 February 2013: European AstroFest-2013
Large Telescope Lucky
Imaging.
• Lucky imaging techniques on
larger telescopes simply will
not
• We remove much of the
turbulent power with a low
order AO system, leaving
Lucky to work as before.
• We used the Palomar 5 m
telescope low-order adaptive
optics system plus our Lucky
Imaging camera.
• We get ~ 40 milliarcsec
resolution in I band.
14 December 2007: U3A, King’s Lynn
Large Telescope Lucky Imaging.
• Globular cluster M13
on the Palomar 5m.
• Seeing ~0.65 arcsec.
• Used PALMAO + our
EMCCD Lucky
Camera.
• With 30% selection,
in the visible we get
~40 mas resolution.
• Highest resolution
image ever taken in the
visible of faint objects.
8 February 2013: European AstroFest-2013
Large
Telescope
Lucky
Imaging.
• The Lucky/AO images resolves <40
mas, ~ 3 times sharper than Hubble.
14 December 2007: U3A, King’s Lynn
Conclusions
• The development of imaging technology has had more
influence on astronomy than almost any other development.
• The photographic plate was central to that development for over
100 years.
• We now have solid-state detectors of extraordinary efficiency
and quality that continue to deliver the most remarkable images.
• The Hubble Space Telescope further revolutionised our
understanding of the universe with unequalled resolution.
• We now also have the possibility of getting pictures from the
ground eight times sharper than those from Hubble.
8 February 2013: European AstroFest-2013
Lucky Imaging Group
Institute of Astronomy
University of Cambridge, UK
[email protected]
8 February 2013: European AstroFest-2013