Our last lecture meetings this session will be:
This will start with wine and cheese (£2 pp), followed by the AGM at 8.45 and then a Scientific Lucky Dip, chaired by Juliette Soester. Please submit interesting scientific questions suitable for a one-minute answer (or deviation) in writing to Julie Anderson before the meeting at Flat 3, 33 Glengall Rd, Kilburn, London NW6 7EL or by e-mail to: firstname.lastname@example.org
Agenda for the Annual General Meeting. 1. Minutes of AGM on 21st June 2001. 2. President's Remarks. 3. Secretary's Report. 4. Treasurer's Report. 5. Election of Officers and Council. 6. Election of Auditors. 7. Report of the Meteorological Section. 8. Report of the Astronomy Section. 9. Any other business.
Council invites further nominations to the above officer posts and ordinary members; such nominees shall be duly proposed and seconded and have agreed to serve if elected.
This month we have a rare opportunity to see all five naked-eye planets lined up for our delectation. Look at the north-western horizon after sunset and, weather permitting, you will see them all in a line descending from Jupiter through Saturn, Mars, Venus to Mercury in late April. Venus will be the brightest at -3.8 magnitude, Jupiter next at -2.0, Saturn fainter at +0.1 and reddish Mars faintest at +1.6 magnitude. Mercury is bright , -1.5, initially and will fade to zero magnitude by the April 30th, disappearing from sight by the naked eye after the 6th May. On the latter date Saturn, Mars and Venus will be in a close group together, with Venus brightest and Mars faintest. By the end of May Mercury and Saturn will have left the evening sky, Mars may in London be too low to see and Jupiter and Venus will be close together. Above them will be the stars Castor and Pollux.
Towards the end of life of a massive star, the star expands into a Red Super giant. It is now thought that this changes into a Blue Super Giant phase shortly before the star blows up catastrophically as a Supernova. Recent observations by the Hubble Space Telescope have shown several ring-like structures associated with the death of such stars. One of particular interest is SN 1987A. (The name means it is a supernova first seen by us on earth in 1987)
The telescope shows three rings, one in the equatorial plane of the star, at a distance of 0.7 light-years. The other two rings are of twice the size and lie at latitudes of plus and minus 45 degrees. Two Japanese astrophysicists have offered an explanation of this using a magnetohydrodynamic simulation .
They argue that in the red supergiant phase a dense and relatively slow stellar wind is generated by the star. The star then evolves into a blue supergiant just before the supernova explosion and this sends out a more dilute but faster stellar wind which sweeps up the previous wind. The winds are anisotropic due to the magnetic field of the star, being slower at equatorial latitudes. What we see as rings are traces of the colliding winds illuminated by the recombination processes following the ionization by the ultraviolet flash of the supernova explosion.
Their computer calculations, albeit with assumptions tweaked to suit, show a three ring structure at 1600 years after the supernova explosion which corresponds closely to that seen by the HST.
Ref 1: Science, 12th April 2002, "Formation of the Three-ring Structure Around Supernova 1987A" by T Tanaka and H Washimi. Back
Peter R Wallis
Last updated by Julie Atkinson 17-Aug-2002