Using the principles behind Einstein’s General Relativity,
is it possible to create a space based telescope with virtually no Raleigh
Criterion limits?
By: Ringo Bones
I’ve first heard of the working principle of a cosmic
telescope was in an episode of Cosmos: Possible Worlds where Prof. Neil
DeGrasse Tyson explains how a space-based telescope using existing – i.e. late
20th century to early 21st Century technology - could
take advantage of the Sun’s gravitational lensing effect in order to create a
telescope capable of seeing the surfaces of extrasolar planets better than the
ones we currently use like the Kepler Space Telescope. But first, here’s a
brief primer on the principles of gravitational lensing.
The Gravitational lensing effect is a consequence of
Einstein’s General Relativity. Often referred by astronomers as a “natural
telescope”, gravitational lensing occurs when a huge amount of matter – such as
clusters of galaxies – creates a gravitational field that distorts and
magnifies the light from distant galaxies that are behind it, but in the same
line of sight. The effect allows astronomers to study the details of early
galaxies too far away to be seen with current technology and telescope. The
gravitational lensing cause by our Sun’s gravitational field can also be used
in a similar fashion. You can also spot distant extra-solar planets when a star
itself is the interloper if it carries any planets in orbit around it, they
will change - ever so slightly – the momentary brightness during the
microlensing event.
There are already plans for a “viable” cosmic telescope that
could – in theory – make the Raleigh Criterion limitations of the telescopes we
currently use, space based or earthbound, completely irrelevant. The Fast
Outgoing Cyclopean Astronomical Lens – or FOCAL – is a proposed space telescope
that would use our Sun as a gravity lens. The concept of a space-based
telescope that takes advantage of the Sun’s gravitational lensing effect was
first suggested by Prof. Von Eshleman and analyzed further by Italian
astronomer Claudio Maccone and others. In order to use the Sun as a
gravitational lens, it would be necessary to position our space telescope to a
point in space of at least 550 astronomical units away from the Sun.
The proposed FOCAL telescope can actually use current
technology that’s already in use on operational space-based telescopes for
astronomical use, however, there are difficulties. The Voyager 1 and Voyager 2
probes are currently at distances within 147 astronomical units and 122
astronomical units. It took them over 40 years to reach those distances using
rocket technology we currently have – by the way, both Voyager spacecraft were
launched back in 1977. It looks like we won’t be sending space telescopes with
comparable technology to the James Webb Space Telescope to a point in space 550
astronomical units – or 51 billion miles or 82.5 billion kilometers– away from
our Sun. By way of comparison, the dwarf planet Pluto is “only” 3.7 billion
miles or 5.97 billion kilometers away from the Sun.
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