has mass bends light around it through its gravity, not just massive galaxy clusters. This effect is too small to be significant around, say, asteroids, but stars have more than enough gravity to act like magnifying glasses. “Microlensing” is a third class of gravitational lensing we observe that is generated by stars passing in front of (relatively massive) objects; because stars are far smaller than galaxy clusters the images produced are too small to be resolved by our telescopes, but a great increase in light can be observed as the star passes in front of a large object. This light can provide clues as to the nature of the object. Perhaps most prominently, a significant number of extrasolar planets have been discovered through microlensing.
Breakthroughs with Gravitational Lensing
On Earth we are at the mercy of chance alignments of stars and other objects to gain the benefits of microlensing, but the sun is a star itself and has more than enough gravity to act as a lens. If you could position the sun between you and a distant object the sun’s gravity would magnify the image and enable far greater resolution to be obtained than would otherwise be possible. If you move yourself so that the sun is directly in front of an object you wish to magnify, the light from the object that the sun bends comes into focus starting at around 542 AU away from the sun.
542 AU is where you will start to see a ring, arc, or other sort of image (depending on your exact position) of the background object around the sun, greatly magnified. Interestingly, there is no focal point in gravitational lensing; it continues to work no matter what the distance is, as long as it is beyond the minimum distance. This is rather convenient, since as some people (most recently Geoff Landis) pointed out the solar corona will interfere with the lensed image until you’re significantly further away (shrinking the apparent size of the corona). Of course, for observations it may be possible to adjust for such interference and keep one’s telescope at closer range; this would be more convenient if it could be done, since 542 AU is already 75 light-hours away from Earth. This means that it would take over six days to send a signal to the telescope and have it send a signal back to Earth, even at the minimum distance.
How much magnification could be achieved? According to this excellent blog post at Centauri Dreams on the same topic, at these sort of distances the light from a lensed object would be magnified by a factor of 100 million. That’s a lot of free magnification for just locating your telescope a few light days further out. Effectively, the object will appear as it if is ten thousand times closer than it actually is. A planet orbiting Alpha Centauri, for instance, would appear as large and bright as it normally would at 27 AU through lensing, even though it is actually 270 000 AU (4.3 light-years) away.
The Hubble Space Telescope, if placed in such a location, could image any planets of Alpha Centauri as well as it currently images Neptune. This would enable very detailed observations, to a degree astronomers and scientists can only dream about today. Space telescopes of far higher resolution than Hubble could be engineered even today (indeed, the soon-to-be-launched James Webb Space Telescope will have higher resolution), and would be trivial to build for any civilization that can manufacture mirrors and telescope assemblies in space, which will include any spacefaring near-future human civilization.
A 2017 article in Air & Space Magazine estimates that near-future space telescope technology ( detailed by NASA at their website , an interesting read by itself) could, using gravitational lensing from the sun, image a planet 100 light-years away at 10 kilometers per pixel. This would yield a (roughly) 1300×1300 pixel picture of an Earth-sized planet. This opens up the mind-boggling possibility of future scientists studying and children gazing in wonder at galleries of pictures of an alien solar system 100 light-years away that are of comparable quality to t