Why do people love amateur astronomy

Astronomy: This is how extraterrestrials could discover the earth

Astronomers don't just worry about how humans might discover extraterrestrial life forms. Sky explorers ask themselves again and again how possible extraterrestrials us would pay attention. Halfway clever aliens would only need telescopes with which they watch as our earth passes in front of the sun and obscures it minimally. This not only made it possible to determine the size and orbit of our homeland, but also the composition of its atmosphere.

With this transit method, terrestrial astronomers have already detected thousands of exoplanets. However, the procedure only works for planets with an orbit whose edge points in our direction. Only in this case do the planets, from the observer's point of view, periodically move past their parent star. Ultimately, therefore, only a small part of the exoplanets present in space can be detected by transit: The orbital plane of most planets is tilted so that the planets never cast their shadow in our direction.

Conversely, the same applies to the earth: it would only be observable from very specific angles using the transit method. Researchers have repeatedly estimated how many stars in our neighborhood fall into this "earth transit zone". Astrophysicist Lisa Kaltenegger from Cornell University and a colleague have now come up with a new estimate: Within a radius of 326 light years - astronomers speak of 100 parsecs - there are 1004 star systems from which one would see the earth transiting in front of the sun , write the researchers in the "Monthly Notices of the Royal Astronomical Society".

Kaltenegger and her colleague Joshua Pepper rely on the latest available measurement data from the astrometry satellite Gaia and the exoplanet telescope TESS. How many of the stars in the earth's transit zone are home to life-friendly planets, the two of them cannot yet say. The list they have compiled can be a starting point when it comes to looking for radio messages in a targeted manner - perhaps there will be someone who wants to tell us something.