Q & A

Hello Brian, i'm a big fan.? I'm only thirteen, but I've read a book from Patrick Moore, "The Atlas of The Universe", and I've seen pictures of the sun.? I saw one of the sunspots, and it kept moving diagonally to the right. Does this mean the sun rotates?

Alex Mullins - Phoenix, Arizona

Dear Alex,

I'm very happy to hear you are already into Astronomy at the age of thirteen ... I was too, and with Sir Patrick Moore's books, you are in safe hands ! You know, we have a lot in common ... I did exactly what I think you are doing ... I projected the image of the Sun onto a piece of white card every day for a couple of months (taking care NEVER to look through the Sun through any kind of telescope, or binoculars) and drew the sunspots as I saw them on a succession of circles drawn on a large sheet of paper. I discovered quickly that they were changing a lot in shape from day to day, but also moving across the face of the Sun. Some big ones even made it around the other side, to transit again across the visible face of our yellow star. Later I discovered that the axis of rotation appeared to change too ... as the Earth journeys around the Sun through the year.

Yes, the Sun does rotate - in about 26 days (not far off a lunar month, strangely), but it actually doesn't rotate as a solid body. It's a huge ball of gas, and the rotation period is different at its equator from nearer its poles. The rotation period also appears different because we are standing on the Earth, which is in orbit around the Sun ... we are not travelling at a uniform speed either ... because the Earth's orbit is elliptical, not circular ... so the Sun appears to vary in its rate of spin. I'm sure all this makes perfect sense to you ... it's fun to visualise all this stuff.

There's an interesting account at this URL:
http://brahms.phy.vanderbilt.edu/a103/labs/web_propsun.shtml
They show these two pictures of the Sun on successive days.

I couldn't resist putting them together next to each other like this, because they make a nice stereo pair ... which can be viewed in 3-D ! (see my 'Soapbox' on BrianMay.com for some other stereo's ! ) It's plain to see these groups of sunspots drifting across, as the Sun rotated.

The images at the bottom of the page are even more amazing ....from the SOHO satellite .... also making a stereo ... I must try to find the original large images - they would make a wonderful stereo But I digress!

Thanks for the message, Alex, and I hope Astronomy takes you to great places ...

cheers!

Brian May

I am a fan of your music. I also have an interest in astronomy. I used to narrate planetarium shows at the Science Center in Des Moines, Iowa. We also had a Challenger Center, a space station simulator, and I ran 'missions' to the moon and the comet Hally. Please explain about your song '39' and how it relates to the twin paradox in relativity. Thank you for your time.

Burton Lodwick - Grimes, Iowa, USA

Dear Burton,

Ah ! Narrating a planetarium show is something I have been asked to do recently ... you know, I have always wanted to do that! Maybe you can give me some tips.

OK .. my song - '39

Yes, it was based on the "Twin Paradox" which is a consequence of Einstein's General Relativity theory. You might remember that his Special Relativity (the relatively simple part ! ) only related (sorry !) to inertial frames ... that is, to two observers in uniform relative motion relative to each other ... constant speed. In this situation, Einstein said, it was impossible to do any experiment which would differentiate between the two frames ... they were equivalent. Now in General Relativity, things were very different. In this situation, one observer can be accelerating, and the other not, and the two observers are no longer equivalent. For the observer who is accelerating, time runs at a different rate from the way it passes for the other guy.

This has actually been experimentally confirmed by firing very accurate clocks into space and retrieving them later! The time they tell when they come back is different from an identical clock which stayed on Earth. They have run slow, as perceived by us, as a consequence of their journey. In an extreme case, if we imagine a traveller in a space rocket, accelerating away from Earth, doing a round trip, and touching down again, if the acceleration is huge enough, and the speeds achieved are close to that of light, the astronaut might have aged one year, while his friends on Earth are a hundred years further on ... so, in fact, on the whole, not even around any more. I was very touched by this imaginary story in my head .. visualising a brave spaceman going off in search of new pastures for his family, but returning to look into the eyes of perhaps his daughter, or even his grand-daughter when he returned, instead of his dear wife ! so that is the basis of the song. I heard it in my head as a folk-song ... the kind that gets handed down as a legend, but this time, not in the past, but in the future ... It's a sad song!

"Don't you hear my call, though you're many years away
Don't you hear me calling you?
Write your letters in the sand for the day I take your hand
In the land that our grandchildren knew ... "

Why are his tenses mixed up? I felt he would have to believe in a time outside time, where he could be reunited with his loved ones ... I think we would all like that ... those of us who have lost our nearest and dearest ...

So, like most songs, it has more than one meaning, depending on your mood when you hear it ...

Thanks for the message and the question!

BANG !

Brian May

How did the Egyptians gain a fair knowledge of the stars and their movements? What sort of instruments were used?

Laurie - Las Vegas, USA

The Egyptians knew little about the nature of the Universe, and made the initial mistake of believing that the sky was formed by the arched body of a goddess with the rather appropriate name of Nut. But though they had to depend upon naked-eye results alone, they made good measurements of star positions and invented constellations, very different from those we use. They also constructed an astronomically based calendar, and were particularly concerned with Sirius [which they called Sothis]. Each year when Sirius rose 'heliacally' ie: could be first seen in the dawn sky, it marked the annual flooding of the Nile, upon which the country's whole economy depended.

The Pyramids are aligned with the north celestial pole, then marked not by Polaris but by Thuban [Alpha Draconis]. They are amazingly accurate; how did the Egyptians manage it? About this there are more theories than there are blocks in the Great Pyramid!

The Egyptians used sundials and also water clocks [clepsydrae]. One instrument used for observing circumpolar stars was the merkhet ['indicator']; it consisted of a narrow horizontal wooden bar with a hole near one end, through which the observer looked to fix the position of the star. Another was the palm-rib; here the star was observed through a V-shaped slot cut at the wider end of the bar.

The last and greatest of the astronomers of antiquity was Ptolemy, who flourished around AD150 - but though he lived in Alexandria, he was certainly Greek. He used elaborate quadrants with remarkable success, but his story belongs to the astronomy of Greece, not that of Egypt.

Patrick Moore

Please ask Mr. May to give www.lightpollution.org.uk a 'coat of looking at'. It deals with the hidden effects of light pollution, LP. These effects appear to be having unexpected knock on effects.

Graham Cliff

Yes - I'm very much aware of this, and have been supporting the campaign for control of light pollution for a long time.

I recommend everyone to give this URL a look - it takes about 1 minute! There is more at stake here than just our view of the Stars ... but that is worth rescuing too!

Thank you Graham ... Much appreciated.

Brian May

I struggle to understand the universe, so hopefully this book will help. If possible, how is it possible to measure the size of the universe and how would you know if you reached the end as such?

Nick - New Zealand

Well, Nick, these are questions we all want to ask. In fact, it is not possible to measure the absolute size of the Universe. It was only relatively recently that I understood this. The volume that we are able to see is limited by the speed of light. The light we see at present, from an object, say, 1000 light years away, left that object 1000 years ago. We know the Universe has only existed for
around 14 billion years (only !), and there are good reasons (see the BANG! book ) why we can't quite see light from quite that far back in time.

This means that the extreme upper limit for seeing distant objects must be when they are around, let's say 13 billion light years away. Anything which is much further away from us than this will always be invisible to us, because the light from it simply has not had time to get to us. We can actually see roughly this distance in two opposite directions ! And there is no indication that the Universe is any different in any direction we look - it seems to be, on the largest scales, homogeneous - so it seems likely that we are only seeing a small fraction of the Universe. We can measure the size of the OBSERVABLE Universe - but there is no way of measuring the 'true' size of the thing !

Brian May

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