Flamsteed Astronomy Society

Transit of Venus - FAS Picture Gallery 3

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Dave Redfern snapped this shot of Venus just appearing at the edge of the Sun (lower right) with an excellent prominence (upper left)

The temperature on the surface of the Sun is about 5,800˚ C.   Even at night?  How do we know?  Do we have a very long thermometer?  Not exactly.  In reality astronomers can measure the temperature of the Sun by examining its spectrum -- the spread of colours produced when sunlight from a telescope is passed through a prism, like the rainbow we see when the raindrops are acting as tiny prisms.

Astronomy during the day?  Absolutely!  But you must use the right equipment.  Never, never look at the Sun directly, or through binoculars, or a telescope without a proper filter.  Properly equipped, we can see that the Sun is a complex and beautiful object to observe, and constantly changing.

Star Struck

In the heat of the Sun — Mike Dryland of the Friends’ Flamsteed Astronomy Society shows readers how to observe our Sun safely.    Transcribed from Horizons Issue 16 Spring 2005.

In 2003 the Flamsteed Astronomy Society of the Friends presented the ROG with a Coronado telescope fitted with a “hydrogen-alpha filter”.  This special filter stops most of the light and heat from the Sun inside the telescope and lets us view safely.  The filter lets through light of just one colour named after the hydrogen-alpha spectral line (Hα or ‘aitch-alpha’) produced by glowing-hot hydrogen gas in the Sun and lets us see features on the Sun’s surface.   Sunspots are areas which look darker because they’re made relatively cooler (a mere 4000˚ C) by whirls in the Sun’s magnetic field.  Sunspots come and go, and each can last from a matter of hours to many days.  The total number of sunspots at any time varies over an 11-year cycle.  At the moment we’re nearing the low point in the cycle (which will happen in 2006) so on average there are fewer spots to see for a while.  Prominences are bursts or spurts of super-hot gas shot-out from the Sun, again channelled by its magnetic field.  Through the Coronado telescope these look mostly like little whiskers on the Sun’s edge, but in fact each is big enough to swallow the Earth whole.

 Many visitors to the ROG tell us that they’d like to look through a telescope while they’re at the Observatory.  The Coronado offers the chance to do this during daylight hours.  On the first weekend of each month, weather permitting, a team of volunteers from the Flamsteed Society sets-up the telescope so that visitors can take a peek at what’s happening on the Sun.  On some viewing days hundreds of visitors have taken the opportunity to have a look. 

Dave Woodford answers a question or two on a bright but chilly January afternoon

As we reported in the last Horizons, at the very rare Transit of Venus event on June 8, 2004 over 6,000 visitors came along to see the planet Venus crossing the face of the Sun.  The weather for the Transit was perfect, but that’s often not the case.  Poor conditions wiped-out the Coronado viewings every month from October to December last year.  No wonder John Flamsteed, the first Astronomer Royal, took 40 years to compile his star catalogue, and the Greenwich astronomers eventually moved to Herstmonceux!

It’s a pleasure for the volunteer team to meet visitors and chat with them about the solar viewing and astronomy in general.   Sometimes we bite off more than we can chew.   A visitor from the United States listened very patiently to our faltering explanations before telling us he was responsible for two major instruments on the Hubble Space Telescope!  

Frank Bath applies some fine adjustment

photo Ian McDowell

It was especially hard to convince non-English speaking visitors that we weren’t all barking mad, showing them a featureless orange disk.  But that’s all part of the fun.

A busy September — Ralph Taylor sorts out a minor problem:  photo Mike Dryland

 The Flamsteed volunteer team for the Coronado is very ably organised by Lesley Bound.  If you’d like to get involved or just want to know more about the solar viewings or the society, take a look at our website at www.flamsteed.org or contact us via the Friends Office at the NMM.

Stan Payne & Jane Bendall get some expert help from visitor Chris Stevenson: photo Mike Dryland

More than once a helpful and very expert visitor has rescued the team from some temporary difficulty with the telescope adjustment.  By contrast, in January we discovered it was quite a challenge to explain the image in the telescope when there were almost no significant features to be seen on the Sun that day

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