Free Astronomy Magazine March-April 2024

14 MARCH-APRIL 2024 ASTRO PUBLISHING such as the largest Egyptian and Mayan pyramids. But what instruments should that hypothetical civiliza- tion possess to distinguish details of a few hundred or even tens of meters here on Earth? According to Os- manov, the best solution to detect our greatest and oldest engineering works from so far away would be the (rather obvious) one − to collect the sunlight re- flected by them. A Type II civilization could achieve this by building titanic tele- scopes with very high an- gular resolution, combined with interferometric sys- tems. In astronomy, the interferometric technique uses two or more single telescopes, often very dis- tant from each other, to si- multaneously observe the same celestial object; the data acquired by each in- strument is then combined and processed. By doing so, the resulting angular resolution is that of a sin- gle telescope with a diam- eter comparable to the distance separating the in- dividual instruments. Os- manov calculated that to be able to distinguish the shape of the largest pyra- mids of antiquity from a N ikolai Kardashev was the creator of a method for evalu- ating the level of development of technological civiliza- tions, based on their ability to exploit energy sources. The staircase that bears his name is schematized below.