Free Astronomy Magazine November-December 2024

32 NOVEMBER-DECEMBER 2024 ASTRO PUBLISHING New light on the darkness of the Universe by NASA Michael Buckley Ray Villard J ust how dark is deep space? As- tronomers may have finally an- swered this long-standing ques- tion by tapping into the capabilities and distant position of NASA’s New Horizons spacecraft, by making the most precise, direct measurements ever of the total amount of light the universe generates. More than 18 years after launch and nine years after its historic explo- ration of Pluto, New Horizons is more than 5.4 billion miles (7.3 bil- lion kilometers) from Earth, in a re- gion of the solar system far enough from the Sun to offer the darkest skies available to any existing tele- scope – and to provide a unique van- tage point from which to measure the overall brightness of the distant universe. “If you hold up your hand in deep space, how much light does the uni- verse shine on it?” asked Marc Post- man, an astronomer at the Space Telescope Science Institute in Balti- more and lead author of a new pa- per detailing the research, published in The Astrophysical Journal . “We now have a good idea of just how dark space really is. The results show that the great majority of visible light we receive from the universe was generated in galaxies. Impor- tantly, we also found that there is no evidence for significant levels of light produced by sources not presently known to astronomers.” The findings solve a puzzle that has perplexed scientists since the 1960s, when astronomers Arno Penzias and Robert Wilson discovered that space is pervaded by strong microwave ra- diation, which had been predicted to be left over from the creation of the universe itself. This result led to their being awarded the Nobel Prize. Subsequently, astronomers also found evidence of backgrounds of X-rays, gamma rays and infrared radiation that also fill the sky. Detecting the background of “ordi- nary” (or visible) light – more for- mally called the cosmic optical back-