Snippets from a talk by Colin Stuart
Colin dispelled one common myth about sunlight, which is that light takes about eight minutes to reach the Earth from the Sun. This is true but misleading. Light will indeed travel from the surface of the Sun to us in eight minutes. The energy was though released deep within the Sun and it will take a photon on average about 170,000 years to reach the surface.
He also explained the origin of the rather odd sequence of letters in the classification of stars. An early attempt at classification was done by Wilhemina Fleming in the 1870s. She based the classification on the intensity of the hydrogen spectral line from stars, with A stars having the most intense line, continuing down to P stars having the weakest line. Various other methods were tried until the astronomy community settled on our familiar one, based at first on colour, now recognized as being temperature. Stars retained their earlier letter given by Fleming, while being re-sorted according to the new criterion : hence O B A F G K M
He introduced us (well me at any rate) to the science of helioseismology which developed from detailed observation of Fraunhofer lines showing that the Sun oscillates. This field of study has shown, amongst other things, that the Sun has a central core which rotates as if it is solid (called the radiative zone) and the outer part which rotates as if it is fluid (called the convective zone)
He gave a bizarre example dating from the Vietnam War of the disruptive power of the electromagnetic radiation of a coronal mass ejection. The US had planted mines which they hoped would detonate when a large ship was nearby because of the effect it would have on the local magnetic field. He didn’t say if that was ever effective. What did happen though in August 1972 was these mines just exploded when nothing was near them to trigger the explosion. Other electrical problems around the world happened at the same time and these have now been linked to a major CME from the Sun. Read more about this at this link.
For more from Colin about our Sun and stars, you might like to get a copy of his book “Rebel Star”
Talk given by astronomy writer Colin Stuart
Post written by Katherine Rusbridge
Aug 2021