Re: Can the gravity of the Sun be used to magnify distant planets?

This concept of a gravitational lens telescope is based upon the observation that gravity can deflect the path of light. In fact, this is one of the classic experimental tests of Einstein's theory of general relativity and what helped lead to its widespread acceptance.

[The first such test was conducted during a solar eclipse in 1919. Astronomers took a picture of the sky around the Sun during a solar eclipse. They compared it with a photo of the same location 6 months later. The positions of stars near the Sun, during the solar eclipse, was different than when the Sun was not there. The amount of the deviation was larger the closer the star was to the edge of the Sun (remember stars very close to the edge of the Sun could be seen because the Sun was blocked by the Moon). The amount by which the position of a star changed was in agreement with what Einstein's general theory of relativity or theory of gravity predicted and in disagreement with what Isaac Newton's theory of gravity predicted. The amount by which the stars shifted was small, only about 1/200 of the width of the full Moon.]

In the case of the 1919 solar eclipse, the amount of light deflection was very small. However, one can ask the question, can the gravitational deflection of light near the Sun result in the Sun focussing light like a lens in a telescope does? The result is yes. However, because the Sun is a weak lens, one has to travel quite far away from the Sun for the light to be focussed, about 550 AU (for reference, the Earth-Sun distance is 1 AU and Neptune orbits at about 40 AU).

As the most distant spacecraft (the Pioneers and Voyagers) are only about 70 AU from the Sun, it will be some time before we could put a telescope at the Sun's gravitational focus. Moreover, there's an additional practical difficulty with this "telescope": Observing many different directions requires a fleet of spacecraft. A spacecraft at the Sun's gravitational focus has to look back at the Sun for the "telescope" to work. If we want to look at objects in two completely different directions, we either have to wait for the spacecraft to move between the two focal points or we have to put two spacecraft at different focal points.

Pictures of (weak) gravitational lensing are at the Astronomy Picture of the Day site.