Free Astronomy Magazine March-April 2024

15 MARCH-APRIL 2024 ASTRO PUBLISHING distance of about 3000 light years (in reality those of Giza would be visible even from over 4500 light years), an interferometric array with a base of several million kilometers would be needed. All in all, a feat not too far beyond a modest Type I civilization like ours. Although Osmanov’s attention is fo- cused on this type of solution, we also cannot exclude that an- other, more technologically de- veloped civilization is already using a “stellar gravitational lens” to search for technosigna- tures on other planets. In 1936, Albert Einstein predicted that light from distant objects seen near the edge of the Sun is de- flected and bent toward a focal “point” about 550 astronomi- cal units (82 billion km or 51 bil- lion miles) away from the Sun itself. If we could place an “eye- piece” where the image comes into focus, we could exploit the lensing effect of our star to ob- serve distant worlds with a res- olution sufficient to recognize D iagram of solar gravitational lensing, a theoretical method for using the Sun as a large lens. It is considered the best solution for directly imaging habitable exoplanets. immediately emerged. Insurmount- able for us earthlings, but perhaps not for others. In conclusion, the answer to Os- manov’s question, whether any alien civilizations technologically more ad- vanced than ours can see us or not, is “probably yes, if their number is high enough for one to exist at dis- tances compatible with the space traveled by light re- flected or emitted by artificial terrestrial objects.” Based on current knowledge, astrobiol- ogists tend to reject this possi- bility and believe that if other technological civilizations ex- ist in the Milky Way, they are likely very rare and very distant from each other. The chances that they can come into con- tact are comparable to those of two swimmers, one swim- ming in the Mediterranean Sea and the other swimming in the Pacific Ocean. In theory, they could meet, but in prac- tice they don’t have enough energy and time. Z aza Osmanov is the author of the recent article in Acta Astronautica , in which he states that the first terrestrial technosignatures could be detected by civilizations more technologically advanced than ours at distances of a few thousand light years. artificial megastructures. Already in 1993, a mission called FOCAL (acronym for Fast Outgoing Cyclo- pean Astronomical Lens) was pro- posed to the European Space Agency to exploit the potential of the solar gravitational lens, but the idea was not followed up due to the insur- mountable technical difficulties that !