Solar sails are the only method of spacecraft propulsion in which no fuel is needed. Until recently spacecraft powered by solar sails were the stuff of science fiction. However, following the success of the Japanese spacecraft IKAROS in 2010 the crowd-funded Light Sail 2 spacecraft in 2019 and NASA's ACS3 in 2024, spacecraft powered by… Continue reading Solar Sails: Fuel-Free Space Travel
Lunar libration is a 'wobble' caused mainly by the Moon’s elliptical orbit and axial tilt. It allows us to see about 59% of the Moon's surface over time, effectively revealing 18% of the 'far side' that would otherwise be hidden. This post discusses this interesting phenomenon. Updated 7 January 2026 Many people think that the… Continue reading How we can see some of the Moon’s far side
In March 2019 the American Vice President Mike Pence surprised many people when he announced an extremely ambitious plan to put American astronauts on the Moon in 2024. NASA named its new crewed Moon programme Artemis, after Apollo’s sister in Greek mythology. Perhaps unsurprisingly, the dates have slipped since this extremely ambitious announcement. After numerous… Continue reading NASA’s Artemis Moon Missions
The Oort Cloud, theorized by Jan Oort in 1950, is a vast, icy structure beyond the Solar System, containing trillions of objects. It is divided into the sparse outer cloud and the denser, doughnut-shaped inner cloud. Evidence for its existence includes the orbits of long-period comets. Galactic tides and interactions with giant planets likely contributed to its formation and distribution of icy bodies.
Update 30 August 2025 I have extensively expanded and rewritten all three “A Short Guide to…” e-books. I will make these books available on Kindle for a competitive price. However, in future I won’t do any deals where I offer free or discounted prices on these books for a limited time period. I believe the… Continue reading eBooks from Explaining Science 2024
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