How the observation of a small anomaly in a distant moon's orbit led to a discovery of, literally, astronomical significance.Weston spins thin historical records into an account of the career of 17th-century Danish astronomer Ole Romer from schoolboy days through nights spent watching the skies through a self-built telescope at the court of Louis XIV to final years as a renowned scientist (and police chief). Noticing that Jupiter's moon Io seemed to speed up and slow down on a regular schedule as it passed behind its planet, Romer not only concluded that light did not propagate instantaneously (a radical notion then), but, using the relatively crude clocks and other instruments of the time, came up with a wrong but close estimate of its speed. Along with retracing Romer's line of reasoning, the author explains how other researchers of the time and later roughed out the distances between major members of the solar system and refined those measurements over time, then closes with nods to Einstein, astronomical distances, and light's truly mind-bending pace. Evans tucks diagrams and mathematical calculations as well as banter and fanciful details into her lighthearted cartoon illustrations, wedging single and sequential panels of Romer and others at work into views of starscapes and planetary surfaces. Human figures in the art are white and predominantly male.A significant, unjustly obscure highlight from modern science's early days. (timeline) (Informational picture book. 8-12)

How the observation of a small anomaly in a distant moon's orbit led to a discovery of, literally, astronomical significance.Weston spins thin historical records into an account of the career of 17th-century Danish astronomer Ole Romer from schoolboy days through nights spent watching the skies through a self-built telescope at the court of Louis XIV to final years as a renowned scientist (and police chief). Noticing that Jupiter's moon Io seemed to speed up and slow down on a regular schedule as it passed behind its planet, Romer not only concluded that light did not propagate instantaneously (a radical notion then), but, using the relatively crude clocks and other instruments of the time, came up with a wrong but close estimate of its speed. Along with retracing Romer's line of reasoning, the author explains how other researchers of the time and later roughed out the distances between major members of the solar system and refined those measurements over time, then closes with nods to Einstein, astronomical distances, and light's truly mind-bending pace. Evans tucks diagrams and mathematical calculations as well as banter and fanciful details into her lighthearted cartoon illustrations, wedging single and sequential panels of Romer and others at work into views of starscapes and planetary surfaces. Human figures in the art are white and predominantly male.A significant, unjustly obscure highlight from modern science's early days. (timeline) (Informational picture book. 8-12)