The Sun in Hydrogen-Alpha (Ha)

Talk to the Society on 21st July 2004 by Bob Turner

      Bob Turner is member of Worthing Astronomical Society, with an interest in astronomy going back more than fifty years.  He works professionally with Bristol University and Kodak on photographing the sun.  He also told the meeting that at present he is one of only 12 serious solar observers in the UK using hydrogen-alpha filters.

      He began by talking about what we see of the sun in white light and described the 11-year sunspot cycle, using the butterfly diagram to show how spots begin to appear in the higher latitudes and progressively appearing closer to the suns equatorial belt. He also showed us a useful graph suggesting that good wines are produced at sunspot maximum and poorer wines at sunspot minimum.

      Bob said that the sun is composed of about 80% hydrogen and 20% helium with very small amounts of heavier materials in the core.  He explained that just outside the core, which has a temperature of 13 to 15 million degrees, is an area called the radiation zone where the temperature is high enough and the pressure strong enough to force the nuclei of hydrogen atoms to fuse into helium, creating photons of energy in the process that bounce around inside the sun, and due to radiation pressure work their way towards the sun’s surface, a journey taking as long as a million years.  Just below the surface is a turbulent layer called the Convection Zone, and once having traversed this, these same photons only take ten minutes to reach earth.  The amount of energy radiated from the surface of the sun is estimated to be about 24,000 Kw per square metre!  .  The temperature at the surface of the sun is about 6000 to 7000 degrees.

      We were shown comparisons of the sun in white light and through a hydrogen-alpha filter.  Sunspots were visible in white light, but hard to see in Ha, although many other anomalies were now visible such as the granular structure of the sun’s surface, solar flares, bridges, “hedges” and spicules.

      In Ha, flares were most visible around the rim of the sun but we could see them clearly on other  areas of the surface.  Flares lasted usually only two or three minutes.  Sunspots are caused by enormous magnetic fields resulting from the movement of particles at the surface of the sun and producing a dynamo effect.  Most spots are bi-polar; two adjacent spots near having opposite polarity.  Bridges of material could be seen leaping between pairs of spots.  Bob said that bridges tended to last between five and ten minutes.  Next, he talked of “hedges” that looked just like their name, with long strands reaching out into space.  These, he explained often last for months.   Spicules were much shorter strands, resembling grass sprouting up between super-granular cells on top of the photosphere.

      Most of the Ha radiation we see originates in the Chromosphere about 6,000 metres above the Photosphere.  Bob produced a “professional” spectrum which when unrolled reached about 20 metres round the studio.  He pointed to the black Ha absorption line, which was only about a centimetre wide.  We saw how electrons moving from shell to shell around the atom, caused the radiation or absorption of high frequency energy.  The Ha line has a wavelength of 6563 angstroms and is only 1.5 to 2 angstroms wide, although an Ha filter can be slightly tuned by altering the tilt of the filter.  Tuning the filter by up to 25 angstroms helps to pick out different details, such as spicules.

      We saw slides of solar activity made in 1939 and 1946 taken mainly at Mount Wilson observatory.  This was a time of great turbulence, matching the solar activity seen last December.  All these slides were in Ha light. There was one remarkable slide taken in 1908 showing the largest flare ever recorded. 

      Bob showed slides of his own equipment including an f28 refracting telescope and a 3-inch refractor he uses for mobility.  We also saw pictures of a refracting telescope that Bob has managed to achieve f32, and with an Ha filter, tuneable by up to 25 angstroms.  He also mentioned an interesting fact that if a CCD camera is used with an Ha filter, it is necessary to remove the Infra Red filter that most CCD cameras incorporate.

      Finally, Bob gave a brief account of the 14 solar eclipses he has observed.  In 1999 he helped organise the hire of a channel ferry with 1,200 observers on board who observed the solar eclipse from the English Channel with great success, although it did start raining just ten minutes after total eclipse ended.  He was photographing the eclipse in collaboration with Bristol University and Kodak producing some remarkable results, some used by the BBC.

      Bob’s next project is a trip to Egypt to observe the transit of Venus on June 8th this year.  He pointed out that most observers are interested to see the visibility of the Venusian atmosphere, but he is looking forward to being amongst the first ever to see the transit in Ha.

      This was a very well researched talk, and was enthusiastically received by the Society’s members.  Bob’s parting comment was that he would be prepared to return with some of his equipment if the Society was to hold a public daytime event and he was free, - and the skies looked promising.



      The next meeting of the Society is on Wednesday 18th  February  2004.  The Speaker will be Lilian Hobbs and the intriguing title of her talk is “Wish you were here for astronomers”

      As usual, the meeting will be held in the Drama Studio at Uplands College.  The doors open at 7.15 and the meeting starts at 7.30 prompt.





           There will be Observing Sessions on the following Fridays:

20th February

19th March

23rd April

      The sessions meet at 7.30 pm in the Crow and Gate pub, about a mile south of Crowborough on the A26 main Uckfield road.  Then at 8.00 pm the group move onto Ashdown Forest with Sean’s and the Society’s telescopes and possibly others.

      Sean Tampsett suggests that interested members phone him between 6.00 pm and 7.00 pm to make sure the session is going ahead.



      The Membership Secretary would be pleased if members would let her or the Editor know if there is a change to their name, address, email address or telephone number.  If you have recently become the proud owner of an email address and would like to receive the Newsletter this way, please let the Editor know.

      Member, having examined the Society accounts for last year in the quiet of their own homes may have noticed one or two changes in the pattern over six years.  Subscriptions have risen with the slightly erratic increase in membership numbers.  The dip in 2002 was partly due to adjusting the subs due date as we moved to match the Nov/Oct financial year.

      Under the heading of Payments, most members are aware of the steep rises in Hall hire costs levied by the county.  As for other expences, postage costs diminished with the adoption of email Newsletters.  This has greatly helped in keeping costs down.  We should not rely entirely on donations of tea, coffee, bisbuits and Mars bars to provide for catering.  It has been most generous of the donors but it does have the effect of masking the so called running costs.

      We need 54 members to match anticipated expences this year, assuming that the mix of Single (£15) and Joint (£20) members in the last and current year remains the same.  We would like to think that the dozen members who are now three months in arrears have their minds on higher things and had simply forgotten.  Would they kindly search out their pens and cheques and make the Treasurer’s job lighter by sending payments now to – The WAS Treasurer, Broadwater Lodge, Stone Cross Road, Wadhurst.  TN5  6LR.

      It is a bit of a balancing act to keep subs at an affordable level.

      The unsung heroine of fund raising, Valerie (Raffles) Barber has let it be known that we are out of material for in-house raffles.  If you would care to replenish the odd item of stock, kindly contact her. (Chairman’s phone)



      The Society has been contacted by a Mr. Stewart Bowler on 01892 782016 who wishes to sell a ‘scope on behalf of a friend who has poor health and is giving up the interest.

       It is a Celestron 8" newtonian with motorised RA equatorial mount and tripod, finder scope 9 x 50, polar alignment scope, plossl eyepieces 10mm and 25mm and Barlow.  Hardly used.  It cost £750 six months ago and he wishes to sell for £300.  A bargain I think!

      Any interested member should contact Mr. Bowler direct, mentioning the Society.




Chairman: Murray R. Barber        01892 654618


Treasurer: Ian Reeves                        01892 784255

Editor:        Geoff Rathbone           01959 524727


Publicity &

Web Site:  Michael Harte              01892 783292


Dir. of

Obs:    Sean Tampsett                       01892 667092