Last month’s talk, February 2015

Yet another opportunity for our own Owen Brazell to cover for our planned speaker, who had to cancel.
‘Observing Planetary Nebulae’ was this well-polished offering.
The first one to be observed by human eye was M27 (the Dumbbell), by Charles Messier. M57 was incorporated by Messier into his catalogue, but it was first observed by Antoine Darquier, who described it as a ‘fading planet’
William Herschel could not make sense of them either and kept hoping that he could resolve them into stars if he could make a telescope big enough, but he failed to do so and decided they must be a fluid around a star condensing as it is being born. He discovered about 45, impressive stuff as the NGC has only 94!
Even Lord Rosse thought and said you could resolve a lot of them. (He of the Leviathan of Parsonstown fame)
William Huggins finally confirmed that they were nebulae when he produced a spectrum of the Cat’s Eye nebula (NGC 6543) and found it to be continuous.

Owen then explained how planetaries are formed, by stars nearing the end of their lives and throwing off their outer layers as their cores collapse to produce a white dwarf. The expanding nebula will then dissipate over 20-70 thousand years. The Boomerang nebula is the coldest area in the universe that we have so far seen, at 1 kelvin.

Planetaries are some of the few astronomical objects to show colour, usually a greenish hue. Filters and high magnifications help a lot. The O III filter passes light in the green area of the spectrum. The O III line is one of the few emission lines you will see in their spectra and that can be used as a distance marker for planetaries in other galaxies. This line was first identified as belonging to doubly ionised oxygen by Ira Bowen in 1927. Interestingly, he was mentioned in January’s talk – he conducted research with telescope eyepieces in order to work out optimum magnifications for various exit pupil sizes.

View the partial solar eclipse from Abingdon

On March 20th 2015, The Sun will be eclipsed by the Moon. From Abingdon up to 88% of the Sun will be covered. The society will have a selection of solar telescopes and eclipse glasses for members of the public to come and view this rare event. At maximum coverage the Sun will appear as a crescent with the horns pointing up. Maximum coverage is expected around 9:30am.

We will be set up in Abbey Meadows, near the Abbey Close car park (see the map below). We will be there between 8:30am and 10:30pm.

We won’t see another big partial eclipse like this till 2026 so make the most of this one.

Lets hope for clear skies.

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!

Cheers,
Ian