Castle Point Astronomy Club
Castle Point Astronomy Club Diary
February 2018 by Dave Stratton
Castle Point Astronomy Club


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Wednesday 7th February 2018

Andrew introduced Dave Hudson for his talk:

Extreme Stars – Everything that you wanted to know about stars and a lot less.

Dave began by listing the various topics that he would cover then showed us a chart of the HR diagram which he explained briefly.

He showed a chart listing the various types of star O, B, A, F, G, K, and M. Where O is the hottest and M the coolest. We saw that there is just 1 class O, 3,600 Bs and 17,000 As. He added that 76% of stars are class M.

M and L dwarfs make up approx half the mass of our galaxy despite being so small.

We learnt that Apparent Magnitude is how bright an object appears to our eyes. Absolute mag is a way of comparing how bright an object really is at a standard distance. Absolute magnitude is slightly more complicated. It is the magnitude of an object if it were 32.6 light years away that´s 10 parsecs. This allows stars to be compared precisely.

Dave explained that a star’s light could be analysed by splitting it into its spectra and then studying the absorption lines to learn the elements present.

The mass of a star is very important it controls the degree of compression and affects the internal temperature and luminosity.

He explained how stars burn very simply and said that the smaller the star the longer it would last and very large stars do not last long at all.

Coolest and Faintest Stars

Dave showed us a slide with cutaway stars showing how the heat is moving in a small star. The smallest have a single circulating system as they get bigger the centre is radiating and the outer circulating – larger again and it is a combination of these systems.

He said that the minimum mass of a star is in the order of 8% of the Sun with a surface temp. of 2000K.

A star like the Sun will last 10 billion years. However a star of 0.8 of the mass of the Sun has a life of 13 billion years. Below G8 no stars have died yet as the universe is only 13.7 billion years old.

The Sun will go into a giant phase at 5 billion years in the future. It will swell and brighten 1000 times swallowing Mercury. When the core Hydrogen burns it swells possibly engulfing Venus and even Earth - the temperature will be 2000 to 2500K. Eventually the outer layers are blown away leaving a naked core.

Hottest Stars

White Dwarfs are amongst the hottest the core gets hotter, as it contracts the electrons move faster when they get to a certain speed they can´t get any closer and produce an outward pressure this initially slows then stops the star´s contraction and it becomes a white dwarf with a mass of 0.55 to 1 of the Sun. The temperature increases from 25,000 to 100,000K. Total luminosity is 1000 times that of the Sun, but mostly in the ultra voilet which we cannot see.

Brightest Stars

He said the first stars we see in the evening are the summer triangle of Deneb, Vega and Altair. Deneb and Vega look about the same, but Vega is 25 light years away and Deneb is 2600 light years away. It is 200,000 times brighter than the Sun. If it were at Vega´s distance it would be magnitude -8.5 or 40 times brighter than Venus making it visible in daytime and cast shadows at night.

Largest Stars

Dave said that red super giants are very rare – about one in a million are in this category. They are all class M with temps below 3,800K. They evolve from stars above 10x Sun. Betelgeuse is 775x Sun it would extend to 3.6 AU between Mars and Jupiter. It is thought to have two companions.

Antares is bigger at 900 times the Sun and would extend to 80% of Jupiter´s orbit. VV Cephei is 1,900 times the Sun and would nearly reach Saturn. You could fit 7 billion Suns inside it.

We saw a series of discs depicting a host of ever increasing star sizes - quite mind blowing.

Smallest Stars

Red dwarfs can be smaller than Jupiter. A Neutron Star is a celestial object of very small radius (typically 30 km) and very high density, composed predominantly of closely packed neutrons. Neutron stars are thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion, provided that the star is insufficiently massive to produce a black hole.

Oldest Stars

He said the Pleiades were young at 100 million years old, M67 is 5 billion years old. The oldest known - HE 1523-0901 is the designation given to a red giant star in the Milky Way galaxy approximately 7500 light years from Earth - is 13.2 billion years.

Strangest Stars

We saw an image of the Calabash Neb The object is sometimes called the Rotten Egg Nebula because it contains a relatively large amount of sulphur. The densest parts of the nebula are composed of material ejected recently by the central star and accelerated in opposite directions. This material is zooming away at speeds up to one and a half million kilometres per hour. Most of the star´s original mass is now contained in these bipolar gas structures.

The Stingray Nebula is the youngest known planetary nebula. It is located in the direction of the southern constellation Ara, and is located 18,000 light-years away. Although it is some 130 times the size of the Solar System, the Stingray Nebula is only about 1/10 the size of most other known planetary nebulae.

Epsilon Auriga is a multiple star system in the northern constellation of Auriga. It is an unusual eclipsing binary system comprising an F0 supergiant and a companion which is generally accepted to be a huge dark disk orbiting an unknown object, possibly a binary system of two small B-type stars. The distance to the system is still a subject of debate, but modern estimates place it approximately 2,000 light years from Earth.

Amazing.

Wednesday 14th February 2018

Our scribe was away this week, but Mike led a very interesting evening on the various methods of astrophotography available including web cams, digital cameras and cooled CCD cameras.

Wednesday 21st February 2018

Mike said that Phil had a DVD entitled ‘The Far Side of the Moore’, a radio drama about the first Sky at Night transmission in 1957 that he was giving away.

Mike introduced Pater for his talk: Observing Highlights March 2018

He told us about Mercury and said that it was thought that only 1% of the population had seen it. A poll in the room established that we did not conform to that statistic. We saw a chart showing the orbits if Mercury and Venus.

Peter explained that an inferior planet (orbiting inside our orbit) was in Inferior Conjunction when it was between us and the Sun and Superior Conjunction when on the far side. Mercury will be at its greatest Easterly elongation on 15th March and at its best for observing. The steep inclination of the ecliptic at this time helps considerably. At about 18.30 on 15th it will be 30 minutes after sunset and the planet will be 12° above the horizon. Peter stressed that it was not easy to see but Venus would help – it is 4° away and lower in the murk - but of course much brighter. Mercury will be above Venus and a little to the right. Have a go at taking a picture.

Peter said that pre 2006 the solar system had 9 planets. However Pluto got demoted to a dwarf plant. This was controversial but the argument was that there were other dwarf planets that are larger than Pluto.

We saw a chart showing where Ceres was.

Our solar system has: - Ceres, Pluto and Charon, Haumea, Makemake and Eris.

Mike introduced Jane for her News:

NASA GOLD Mission to Image Earth’s Interface to Space

On Jan 25, 2018, NASA launched Global-scale Observations of the Limb and Disk, or GOLD, a hosted payload aboard SES-14, a commercial communications satellite. GOLD will investigate the dynamic intermingling of space and Earth´s uppermost atmosphere — and is the first NASA science mission to fly an instrument as a commercially hosted payload.

Space is not completely empty: It´s teeming with fast-moving charged particles and electric and magnetic fields that guide their motion. At the boundary between Earth´s atmosphere and space, the charged particles —called the ionosphere — co-exist with the upper reaches of the neutral atmosphere, called the thermosphere. The two commingle and influence one another constantly. This interplay — and the role terrestrial weather, space weather and Earth´s own magnetic field each have in it — is the focus of GOLD´s mission.

The Transiting Exoplanet Survey Satellite (TESS) is a two year survey mission that will focus on the discovery of exoplanets in orbit around the brightest stars in the sky. This first-ever all-sky transit survey will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar types and orbital distances.

James Webb Space Telescope is the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems.

´Oumuamua is the first known interstellar object to pass through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory, Hawaii, on 19th October 2017, 40 days after it passed its closest point to the Sun. It is thought to have been in a collision that has caused it to have a tumbling motion.

Juno is a NASA space probe orbiting the planet Jupiter. It was built by Lockheed Martin and is operated by NASA´s Jet Propulsion Laboratory. The spacecraft was launched from Cape Canaveral Air Force Station on 5th August 2011, as part of the New Frontiers programme. We saw a superb close up image of Jupiter taken on 15th February showing detail of the clouds.

The HST has been imaging a mysterious storm formation on Neptune – we saw a video clip of the phenomena.

Jane reported that there are plans to study space weather by placing a probe at LaGrange 5 to look at the Sun before it rotates to present that face towards us.

NASA is to host a space council meeting.

Asteroid Day is an annual global event which is held on the anniversary of the Siberian Tunguska event that took place on 30th June 1908, the most harmful known asteroid-related event on Earth in recent history. The United Nations has proclaimed it be observed globally on 30th June every year in its resolution.

One man´s mission to conquer space - Rocket Lab entrepreneur Peter Beck´s recent launch into orbit of Humanity Star drew a barrage of flak. But he remains undaunted. Last month, from its base in New Zealand, Peter Beck´s space company, Rocket Lab, conducted its first successful attempt to put satellites in orbit. The launch vehicle, the Electron, carried a payload including the Humanity Star, a very shiny, 65-sided, carbon-fibre satellite whose only function is to reflect the sunlight as it spins. Scientists didn´t approve: astronomers claimed it would interfere with their observations, others called it ‘space graffiti’, while the Scientific American described it as ‘satellite vermin’.

Mike introduced Ed with his: Ed´s Stuff

Out come his trusty polystyrene balls mounted on wire supports this time to represent Sirius and its ‘pup’. Ed said that the brightest star Sirius has a companion, Sirius B, that was extremely difficult to see because of the great brightness of Sirius.

Ed showed a chart showing the position of B from now to 2060 – it will be at its greatest elongation for the next 40+ years.

Ed said that Edmund Halley had noticed that some stars moved over the centuries. Ed said that Sirius had moved a lunar diameter over 1000 years.

Frederick Bessel went on to obtain precise positional measurements of Sirius, the brightest star in the sky. His observations revealed that Sirius was slowly changing its position as if it were being pulled around in orbit by the gravity of another star. In 1844, Bessel had a sufficient number of precise observations to announce that Sirius must have an unseen companion. The orbital period of the two stars around each other turned out to be about fifty years.

Astronomers searched for the companion star but couldn’t find it. Finally, in 1862, after Bessel died, the American telescope maker Alvan Clark, while testing a new telescope on the bright star Sirius, actually discovered the companion. It was indeed a star, but so very faint that it was almost lost in the glare of Sirius. Because the companion was about twice as far as Sirius from their common centre of mass, it had to weigh about half as much (like a child twice as far from the centre of a see-saw balancing an adult). Why then was the companion almost a thousand times fainter?

The separation is now known to be 3 to 11 seconds of arc. Ed said he had seen it twice in the last three weeks and showed a delightful HST image. He suggested that 150 to 250 times was a good place to start.

What a lot we got.

Wednesday 28th February 2018

The meeting was cancelled due to Emma and the Beast.


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