Castle Point Astronomy Club
1969-2019 - 50th Anniversary Year
Castle Point Astronomy Club Diary
March 2019 by Dave Stratton


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Wednesday 6th March 2019

Mike introduced our speaker tonight Rosalind Park an Egyptologist who happens to be the wife of our member Gord for her talk on the Dendera Zodiac.

The talk transpired to be too difficult for me to do justice to it here so Rosalind and I agreed that the best way would be for me to consult the internet.

Rosalind said that the Zodiac was originally located in the ceiling of an Egyptian Temple to the Goddess Hathor at Dendera which is on the River Nile in Africa. The ceiling was relocated to the Louvre in Paris which involved cutting it into three pieces. The one in Dendera is a replica with the original on display at the Louvre.

The zodiac is a Planisphere or map of the stars on a plane projection. The decans are groups of first-magnitude stars. These were used in the ancient Egyptian calendar, which was based on lunar cycles of around 30 days and on the heliacal rising of the star Sirius.

Its representation of the zodiac in circular form is unique in ancient Egyptian art. More typical are the rectangular zodiacs.

The celestial arch is represented by a disc held up by four pillars of the sky in the form of women, between which are inserted falcon-headed spirits. On the first ring 36 spirits symbolize the 360 days of the Egyptian year.

On an inner circle, one finds constellations, showing the signs of the zodiac. Some of these are represented in the same Greco-Roman iconographic forms as their familiar counterparts (e.g. the Ram, Taurus, Scorpio, and Capricorn, albeit most in odd orientations in comparison to the conventions of ancient Greece and later Arabic-Western developments), whilst others are shown in a more Egyptian form: Aquarius is represented as the flood god Hapy, holding two vases which gush water. The similarities of unfamiliar iconology with the three surviving tablets of a "Seleucid zodiac" and both relating to kudurru, "boundary-stone" representations.

The famous Zodiac of Dendera confounds today's visitors who may look for a reflection of modern-day astrological beliefs. This bas-relief actually represented a night sky scape, on the ceiling of a chapel in the Temple of Hathor at Dendera, where the mysteries of the resurrection of the god Osiris were celebrated.

The sandstone slab comes from the domain dedicated to the goddesses Hathor and Isis at Dendera. It was part of the ceiling of one of the chapels where the resurrection of Osiris was commemorated, on the roof of the great Temple of Hathor.

The vault of heaven is represented by a disc, held up by four women assisted by falcon-headed spirits. Thirty-six spirits or decans around the circumference symbolize the 360 days of the Egyptian year. The constellations shown inside the circle include the signs of the zodiac, most of which are represented almost as they are today. Aries, Taurus, Scorpio, and Capricorn, for example, are easily recognizable, whereas others correspond to a more Egyptian iconography: Aquarius is represented as Hapy, the god of the Nile flood, pouring water from two vases. The constellations of the northern sky, featured in the center, include the Great Bear (Ursa Major) in the form of a bull's foreleg. A hippopotamus goddess, opposite Ursa Major and Ursa Minor, represents the constellation of the Dragon.

The five planets that were known at the time are associated with certain signs of the zodiac: Venus "the god of the morning" is behind Aquarius, Jupiter "Horus who reveals the Mystery" is near Cancer, Mars "Horus the Red" is directly above Capricorn. Mercury is called "the Inert" and Saturn "Horus the Bull". This particular configuration of the planets among the constellations occurs only about once every thousand years; an astrophysicist has dated it between 15 June and 15 August 50 BC. Two eclipses are represented exactly where they occurred. The solar eclipse of 7 March 51 is depicted as the goddess Isis holding a baboon (the god Thoth) by its tail, signifying her attempt to stop the moon from hiding the sun. The lunar eclipse of 25 September 52 is represented by an udjat-eye (the "whole one"), because a lunar eclipse only occurs when the moon is full.

The Zodiac of Dendera was transported to France in 1821 with the permission of Egyptian ruler Mohamed Ali Pasha. It is one of the most famous Egyptian monuments preserved in France.

It should be interpreted as a map of the sky rather than a giant horoscope or a perpetual astrological tool. However, the Egyptians believed that certain constellations and decans could have a negative influence on their destiny or health.

The representations of the signs of the zodiac as we know them today did not appear in Egypt until the Greco-Roman Period. This monument reflects the way Egyptian cultural elements merged with Babylonian and Greek astronomical and astrological theories, as a result of the Assyrian and Babylonian deportations of the 8th and 6th centuries BC, and the Persian and Greek invasions of the 6th and 4th centuries.

Most enjoyable.

Wednesday 13th March 2019

Ted officiated today and gave us a reminder for the Open Night this weekend and introduced our newest member Chris for a short item on: Using an iPhone as an aid to lining up a device.

Chris began by advising us that he had written a couple of books on astronomy and was a member of the BAA.

He turned on the gyroscope in his iphone and demonstrated its use.

He showed us a clamp that held the phone and allowed it to be attached via a standard camera thread to a ball and socket device.

With the assembly attached to a tripod he showed how it can be pointed at say Sirius and then you could ‘step’ to another object. He added that a cheap £10 red dot finder attached to the ball and socket helped.

Ted introduced Dave Sm for his advertised talk: Variable Stars.

Dave began by showing a delightful image of the ET cluster in Cassiopeia he said it was a 10 wide image with about 40,000 stars.

Apparently the Sun is a variable star he had a couple of detailed solar scope images for us to see – it showed a very active surface as it was an old pic - currently our star is rather quiet.

He explained that as a star gathers material gravity compresses it ever smaller until the fusion process balances gravity and we get equilibrium. We saw a nice diagram that explained the process.

Why observe variable stars? In 1900 only a handful of were known. By 2018 it was in excess of 150,000! They are still being discovered regularly and not just by professionals with their fancy surveys. By amateurs as well!

We usually observe variable stars by: Watching (measuring) their variations over time, be it hours, days, weeks or months These variations take the form of changes in brightness (magnitude). This can be by eye, with binoculars or a telescope or by electronic means using either a CCD Camera or a DSLR. Dave showed us several light curves he had plotted.

When it comes to observing VS the naked eye works well with some but bins improve the situation.

Which Binoculars to use? Answer – any! Well, almost any.

10 X 50s or 7 X 50s are good. Anything more than 10X can be difficult to hold unless mounted.

8X40s are lighter and also good. Don’t be fooled into getting a pair of 20X80s – they need to be mounted. If you’re not sure if you really are going to take up binocular observing don’t spend more than say £50.

Which Telescope to use? Answer – any! Alt-az; Equatorial, Refractor or reflector, Newtonian, Schmidt-Cassegraine, etc. Wide field of view is good.

We saw a pic of his dome housing his Celestron Edge HD Optics scope which he was allowed to buy recently with the kind permission of his lady wife.

He explained the nomenclature with the aid of a slide and also told us about getting finder charts and how to interpret them.

He recommended a Binocular Variable Star Chart which is available for £1.

Three main types of Variable Star: - Pulsating: Eclipsing: Eruptive:

Pulsating Stars

Variations caused by star physically pulsating – Like a balloon blowing up and down – only outer layers involved.

Periods range from hours to years, depending on type.

The range in brightness from about 0.5 magnitudes to over 10.

We saw a nice image of a pulsating star and a light curve from C792 Cepheus.

The driving mechanism behind "self-excited" oscillations is a special region of the stellar interior where atoms of either hydrogen or helium transition from partly to completely ionized. If the star is compressed, the ionization fraction of these regions increases, raising the opacity of the material and blocking the luminous energy trying to escape from the interior. The increased heat and pressure built up in this layer push the outer layers of the star outward. As these outer layers fall back inward again under the force of gravity, the ionization region gets compressed again, restarting the cycle. The variation in brightness is caused by changes in temperature and radius caused by these motions. For stars on the instability strip, this important layer lies at just the right depth in the star for pulsations to be self-sustaining.

We saw a light curve from V973 Cep. and several others.

Eclipsing Binary Stars

Variations caused by two stars actually revolving around one another - stars must lie in our line of sight. Periods range from hours to many years. He showed us some light curves which are quite fascinating.

Eruptive Stars

These show variations from gentle ones to gigantic explosions we call supernovae.

Many are actually binary stars in which the eruptions are due to an exchange of material from one star to the other, often via an “accretion disc”.

We saw some interesting diagrams explaining how this extraordinary phenomenon is thought to work.

He showed some amazing light curves from OV Boo eclipsing cataclysmic star OV Boo

SUMMARY

Why observe variable stars?

It’s simple and fascinating to watch stars that are billions of miles away changing in brightness, and to learn about these systems from data that is obtained using your own eyes/telescope.

Your data, when combined with other observers’ data can be valuable and unique, and can make a real contribution to science.

Finally, you can make friends all over the world sharing your interest.

He demonstrated AstroImageJ software which he uses to help with his work on these fascinating stars.

What clever members we have.

Wednesday 20th March 2019

Mike said that both the Astro Camp and the Open Night were affected by damp but never mind we have our Family Day in the not-too-distant future.

He reminded us to book our places at the BAA event.

Andrew said that next week he is giving a talk on How the Sky Works Part 1 or if it’s clear we will be observing. He reminded us that although the programme is filling up we still have a few slots to fill.

Ed said that said he was planning to look at some double stars on Monday at Wallasea despite a nearly full Moon.

The next Kelling Heath Astro camp is almost on us. Dave Sm said his ticket is available if anyone is interested.

Mike said it was time for the main event tonight: Members’ Activity Roundup

Andrew was first with some images from his iphone starting with a nice Moon shot taken with the NightCap app on his iPhone through his 5 inch reflector. He also showed some images of the Pleiades and M42 taken through his Meade ETX-70 using the same app.

Ron had some pics from the recent Astro camp just cars and tents as the weather was poor.

Jim had a pic of the total lunar eclipse – he said it was a 3second exposure and had brought out the red colouration nicely. He showed us a diagram of the Moon’s location in relation to the Earth’s umbra and penumbra.

He also had a delightful video of several lunar features. Plus another of a comet moving quickly at mag 7. An excellent image of M42, spiral galaxies M81 and M101 and M33 which he said was the size of the Moon.

He also had a light curve of a variable star in Ursa Major which changed quickly in just 4 hours 20 minutes.

Andy D had shots from his visit to Las Palma which he admitted was inspired by Ted’s talk.

He said that his location was a long way from the mountain top where the professional observatories are sited and he had hired a car to get there. However despite his urban location he said the sky was great. He was located close to the sea and found a ‘Dark Site’ just 10 minutes walk away on the beach almost and right next to a banana plantation which helped shield him from the town. He showed several shots of the location. Also of his set-up which goes into a back-pack including a tripod.

His first shot was a delightful 12second exposure of the Milky Way followed by a 30second one. Then we saw 50 of these stacked – superb. He showed us a very nice composite image of all his pics. He pointed out the central area of the galaxy and had a panorama of the same area. He pointed out many sites of special interest in the images.

At another location next to a lighthouse he made a splendid image of the Milky Way framed by the lighthouse and another tall structure.

As a comparison he showed an image of the Dumbbell Nebula taken from his home that needed 30hours of imaging!

Chris W showed us a lithium Ion battery which he uses to perhaps power a dew heater but can also be used at 5 or 12 volts to power apparatus for up to a week.

Ed had some images and from the last visit to Wallasea. He centred on the Virgo cluster of galaxies halfway between two stars which identified on a chart for us. He had a detail of Markarian’s Chain, a lovely curving arc of galaxies in the galaxy rich spring sky. He said the curve was perhaps 5 or 6 moon diameters across.

He finished with a map showing Burnham-on-Crouch with our meeting place for the Dengie Dark Site and directly across the estuary is Wallasea Island our other Dark Site.

Well packed as usual.


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