May Gallery

Bubble chamber photo of sigma particle decay

Bubble chamber photo of sigma particle decay. The sigma lives too briefly to be seen; its presence is deduced from other particles. A neutrino enters unseen at bottom & collides with a proton in the bubble chamber liquid, producing the sigma & a negative muon. The sigma decays to 1 negative & 3 positive pions, & a neutral lambda which leaves no track but betrays itself when it decays at lower centre (within the loop) to a proton & a negative pion. Negative particles curl anticlockwise, positive ones clockwise in the magnetic field. One positive pion is of lower energy & forms the loop; the muon & one of the pions knock out atomic electrons which produce the two spiral tracks

© BROOKHAVEN LABORATORY/SCIENCE PHOTO LIBRARY

Artwork showing Voyager 2s encounter with Uranus

This artwork, by Julian Baum, shows the Voyager 2 spaceprobe only minutes away from closest approach to the planet Uranus, on 24/Jan/86. Uranus is one of the four great gas giants. It is unique in that its equator, along with its moons and tenuous ring system, is tilted at 98 degrees to the plane of the Solar System. Because of this, Voyager's encounter with the planet and its satellites lasted only about six hours. It also means that in alternate seasons Uranus poles and equator in turn face the Sun. Uranus orbits the Sun once in 84 years and, at present, the planet's south pole faces the Sun, in the midst of a 21 year long summer

© JULIAN BAUM/SCIENCE PHOTO LIBRARY