Multiple shadows on Jupiter

On Saturday morning (24th January) 3 of Jupiter’s satellites and their shadows will cross the disk of the giant planet.

The shadow of Calisto starts to cross Jupiter’s disk at 3:14 GMT. At 4:35 GMT, it is joined by Io’s shadow. Io’s shadow races after Calisto’s shadow and catches up with it at 5:49 GMT when the two will briefly merge. There’s good chance that Io will cross Calisto’s shadow shortly thereafter. At 6:28GMT Europa’s shadow will also start to cross Jupiter. For the next 24 minutes all three satellites will be casting their shadows on to Jupiter’s disk. Below is a simulation of this event.

This is a rare event, so its well worth the effort of getting up for an early start Saturday morning!


Geminids meteor shower on December 13th

The Geminid meteor shower peaks this year on the 13th December. The constellation will be in the east by 9pm and the Moon will not be rising until about 11:30pm.

The map above shows Gemini at 11:30pm on the 13th December just as the Moon is rising. The radiant of the meteor shower is marked. Look to the south for the best views of any meteors. Rates are predicted to about 100 per hour, although this assumes idea conditions. Don’t forget to wrap up warm!

Clear skies,
Ian Smith

Novembers talk, “Exploring our star from space”

Professor Richard Harrison is the head of the Space Physics Division and Chief Scientist at RAL. He has been a solar physicist for 35 years and he graced us a few years ago on the subject of hardware in space, exploring the Sun, in particular with the two STEREO observatories (=Solar-TErrestrial-RElations-Observatory) which were launched in October of 2006. Both have two helioscopic imagers (HI), one looking at the Sun and one looking past the Sun. The craft were launched so that one lagged behind the Earth and the other went ahead (hence: STEREO Ahead and Behind). I pinched that from my April 2011 writeup and I want to say I am glad that we have such amazing gadgets monitoring the Sun, especially as we have been watching a major sunspot group 12192 reappearing after causing concern in October. Bob may have something to say about it, please!
The SOHO solar observatory has been going strong for 19 years and its main observing wavelength is in UV, 171 Angstrom (1710 nm). STEREO has been observing in 304 Angstrom, a near UV wavelength which picks up helium radiation, so is ideal for identifying CMEs (coronal mass ejections), potentially harmful to us on Earth.
STEREO A has a slightly smaller orbit than STEREO B is now about to lap its partner on the inside as they come together in the middle of 2015, by which time we will be on that side of the Sun in our orbit. Both satellites are tilted slightly so that they don’t look directly at the Sun – they only need to capture one ten million millionth of the Sun’s light. We do lose information at times when the Sun is between us and them, as happened when we temporarily lost contact with STEREO B last month.

We are lucky that so much is happening just down the road from us. The RAL space facility has 230 staff and has had a part in designing, building and testing 208 instruments in space. At present it is situated near the Harwell mound (Oxfordshire cross-country runners will know that well by now) but will be moving to another site near the main entrance, where the ESA (European Space Agency) will also be setting up a site.

The forerunner to RAL started 82 years ago with the Ionosond pole, sending pulses into the ionosphere to be picked up by ground-based radar.

As before, Professor Harrison was enthusiastic and informative, and he managed to give a plug for an interesting website, Urthecast, which is a high resolution video from the ISS, allowing you to monitor the Earth. Magic!