Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 August 20 The Universe in Hot Gas Credit & Copyright: James Wadsley (McMaster U.) et al. Explanation: Where is most of the normal matter in the Universe? Recent observations from the Chandra X-ray Observatory confirm that it is in hot gas filaments strewn throughout the universe. "Normal matter" refers to known elements and familiar fundamental particles. Previously, the amount of normal matter predicted by the physics of...