22 May

2003: On 22 May 2003, the NASA/ESA Hubble Space Telescope (HST) spotted mysterious 'jets' emerging from planetary nebula Henize 3-1475. Astronomers have nicknamed it the 'Garden-sprinkler' Nebula.

'Jets' are long outflows of fast-moving gas found near many objects in the Universe, such as around young stars, or coming from black holes, neutron stars, and planetary nebulae, for example.

The origin of jets in the Universe is unclear, but they appear to originate in small regions of space where even Hubble's sharp vision cannot penetrate. To produce a jet, you require some sort of nozzle mechanism. So far, these theoretical 'nozzles' remain hidden by dust that obscures our view of the centres of planetary nebulae.

Despite decades of intense effort, there is no single example of a jet whose origin is clearly understood. The curious S-shape and extreme high speed of its gaseous outflow gives Henize 3-1475 a special place in the study of planetary nebulae.

1995: On 22 May 1995, the NASA/ESA Hubble Space Telescope (HST) captured an image of Saturn as the planet's ring system turned edge-on. This ring-plane crossing occurs approximately every 15 years when the Earth passes through Saturn's ring plane.

For comparison, the top picture here was taken by Hubble on 1 December 1994 and shows the rings in a more familiar configuration for Earth observers.

The bottom picture was taken shortly before the ring plane crossing. The rings do not disappear completely because the edge of the rings reflects sunlight. The dark band across the middle of Saturn is the shadow of the rings cast on the planet (the Sun is almost 3 degrees above the ring plane.) The bright stripe directly above the ring shadow is caused by sunlight reflected off the rings onto Saturn's atmosphere.

Two of Saturn's moons are visible as tiny starlike objects in or near the ring plane. They are, from left to right, Tethys and Dione.