Earth is losing some of its glow, a study published in Geophysical Research Letters last week shows. It appears climate change and a natural climate shift have essentially scuffed up our planet. From a report: The study takes a look at earthshine, or the light reflected from the planet that casts a faint light on the surface of the Moon. It’s also known as the Da Vinci Glow, because Leonardo da Vinci was the first person to formally write about it. Research has advanced quite a bit since da Vinci’s writing 500 years ago, and the new findings use two decades of earthshine data collected at Big Bear Solar Observatory using a special type of telescope to view the Moon. The best time to observe earthshine is when the Moon is waxing or waning. Look at the Moon then, and you may be able to make out a faint outline of the whole Moon in addition to the sliver brightly illuminated by the Sun. That ghostly outline is thanks to earthshine, caused by the sunlight reflecting off our planet.
The observatory is perfectly situated to measure earthshine for 40% of the planet, spanning the Pacific and parts of North America. Analyzing the data for roughly 800 nights between 1998 and 2017 showed a small but significant decline in earthshine. There were some year-to-year shifts, but the paper notes that those are “quite muted, with a long-term decline dominating the time series.” The scientists used satellite data to gauge what drove the dimming. Land, ice, clouds, and open ocean all have different levels of reflectivity that contribute to earthshine. (The reflectivity of different surfaces is also referred to as albedo.) The findings point to the disappearance of clouds in the tropical Pacific as the culprit in dulling Earth’s shine. “The albedo drop was such a surprise to us when we analyzed the last three years of data after 17 years of nearly flat albedo,” said Philip Goode, a researcher at New Jersey Institute of Technology and the lead author of the report, in a statement.
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