Flamsteed Astronomy Society

‘Timings’ a talk by Greg Smye-Rumsby — October 10, 2011

Greg Smye-Rumsby

[Pic: Grey Lipley]

Report by Chris Sutcliffe

This lecture was presented by Greg Smye-Rumsby who is on the Astronomy staff at the Royal Observatory Greenwich; as part of this role, he presents an “Evening with the Stars” when he operates the 28” telescope; he is a planetarium presenter and he also leads astronomy classes. In addition, he produces some of the graphics for ‘Astronomy Now’ magazine.

Greg introduced us to some interesting perspectives on ‘Timings’:

> We are all going to die; we do not know when but it is the most certain fact of life!

> The likelihood of being hit by an asteroid. The asteroid belt between Mars and Jupiter is the cause of less concern than was previously thought. However, the asteroid Apophis will come close on Friday 13 April 2029. On the Torino scale (a risk hazard  measurement) of 0 - 10, Apophis was 2, but is now 1.In 2036, there is a 1 in 250,000 chance that it will hit us!

Greg mentioned a ‘gravitational keyhole’ When an asteroid passes by a planet, the gravitational attraction of the planet pulls on the asteroid and deflects it from its original trajectory, thus changing its orbit. The amount of change depends on the distance of closest approach of the asteroid to the planet: the closer the asteroid comes to the planet, the larger the deflection will be.

If an asteroid were to pass a planet at a distance that changed its orbit by just the right amount, the asteroid would collide with the planet on its next fly-past. The distance which causes this to happen is the location of the keyhole.

> EELT (European Extremely Large Telescope). This telescope will have a mirror 40 metres across enabling astronomers to view the universe as it was billions of years ago.  It will look for the faintest objects (or bright ones which are massive distances away). By contrast, the 5 metre telescope at Mount Palomar looks at objects as they were just millions of years ago.

When a star first ignites, its light is greater than the light output of its galaxy. The very first stars were made of hydrogen and helium, but when they die, they become super-alchemists creating 26 elements. We do not know whether a particular star was there before its galaxy.  The temperature at the time of the “Big Bang” was 10 to the power of 42 degrees K, 13.7 billion years ago. The elements Hydrogen and Helium were produced at this time. (All the other elements were made later inside the stars). After a million years, some of the brightest stars which were massive became supernovae .

In 1054, a star died in the Crab nebula, and the brightness would have been such that it lit  up the day-time sky.  The pulsar (the collapsed core of a massive star) in the centre of the Crab nebula is 25 km in diameter and rotates 30 times a second emitting massive amounts of  gamma ray radiation which is picked up on Earth as pulses.

> Eclipses and the moon. The next total eclipse of the sun visible in the UK will be on 23 September 2090.  A company is proposing to fly to the moon and back in 7 days by Soyuz  spacecraft.  From the moon, the Earth is always visible and four times bigger in the lunar sky than the size of the moon in our sky.

> The Antikythera mechanism.  Discovered in the early 1900s. The antikythera mechanism is currently housed in the Greek National Archaeological Museum in Athens and is thought to be one of the most complicated antiques in existence. At the beginning of the 20th century, divers off the island of Antikythera came across this clocklike mechanism, which is thought to be at least 2,000 years old, in the wreckage of a cargo ship. The device was very thin and made of bronze. It was mounted in a wooden frame and had more than 2,000 characters inscribed all over it. It is believed that this instrument was a kind of mechanical analog computer used to calculate the movements of stars and planets in astronomy. It is amazingly sophisticated and able to show that the moon goes through exactly the same phases and is in the same position in the sky every 18.6 years.

> On 22 October 1707, Sir Cloudesley Shovell was shipwrecked on the rocks off the Isles of Scilly, which prompted the setting up of the Board of Longitude in 1714 with prize money of £20,000 (about £6 million in today’s money) for coming up with an accurate means of measuring longitude. John Harrison won the prize but he died three years later aged 83.

> Bradley’s Meridian was the active meridian at Greenwich for 100 years until 1851 when Airy’s meridian was adopted (recognised as the prime meridian of the world in 1884).  Bradley’s Meridian can be seen at Greenwich slightly to the west of the prime meridian.

> A leap year occurs every four years and can be readily calculated as the year is divisible by 4 . But century years must be divisible by 400 to be leap years.  Therefore 2400 will be a leap year!

> Ole Romer calculated the speed of light in 1676 by timing the eclipses of Jupiter’s moons when the planet was at different distances from Earth.

This was a fascinating lecture which presented us with many thought - provoking facts, and concluded with a number of questions which Dr Greg was pleased to answer.

Chris Sutcliffe



Antikythera Mechanism