Wadhurst Astronomical Society Newsletter July 2020

Welcome to the July newsletter and I hope you find some of the articles interesting. We begin with the report from the first full WAS Zoom meeting which was very successful and attended by at least 22 guests. It was hosted by Brian Mills, our Chairman with two presentations that performed very well, where questions were able to be put using the “Chat” button and answered almost as though we were back at Uplands, except for the absence of Jim Cooper’s famous tea, coffee and biscuits.

To start the meeting Phil Berry outlined the Zoom programme followed by his introduction to John Lutkin, the Society’s Treasurer who gave our main talk.

John specialises in the effects of radiation on human cells and has published a number of papers on the subject. He was also the protection adviser for the southeast of England.

Radiation – the Limiting Factor Dr John Lutkin

John opened by saying that “Once you’re out of the Earth’s magnetosphere and are in an aluminium can, you are in serious trouble!”

It was known over a hundred years ago that the x-rays being used by radiologists of the day were producing problems and were dangerous to human tissue.

It was explained that the problems begin to occur when radiation energy interacts with human tissue creating ionisation.

There are three main kinds of radiation; alpha particles, beta that are electrons and gamma and x-rays which are the ionising group of electromagnetic radiation.

We were told that when an energetic particle hits an atom it can knock off an electron which either disappears or can cause damage to the cellular structure. This then leaves an ion which itself becomes chemically active.

Alpha particles are relatively large and produce a lot of ions in the human tissue. Beta is relatively sparse and causes less damage. Gamma and x-rays pass through human tissue and are used to take pictures, differentiating between bones and soft tissue. John said that it was the electrons produced by the secondary effect that cause the ionisation damage.

Cosmic Rays, mainly protons, were described as having massive energy enabling the formation of large numbers of ions.

So, following radiation exposure there can be a chemical change, there are molecular changes to DNA, RNA and enzymes causing the cell to change or die. John told us that cell-death is dealt with by the body in the normal way but changes to the DNA can be a serious issue.

Part of the DNA strand

He explained that if ionising radiation causes a single break in the DNA chain, this is usually repairable. A double break is less likely to repair and the cell may die but if a chemical change occurs this is not repairable and may lead to cancer or mutation.

There are two effects of ionising radiation on the human body; one where just the individual is affected and the other where the affect becomes hereditary. The results of radiation are a bit of a lottery we were told. After receiving radiation, there is a probability of some effect. Many of the risks are still based on studies from Hiroshima and Nagasaki. 1

John spent some time explaining the ways of measuring radiation quantities. Absorbed dose is the measure of energy absorbed in Grays (Gy), the Equivalent dose to a particular organ is measured in Sieverts (Sv) and the Effective Dose measures the overall effect on an individual; different tissues have different sensitivity. The inter-relationship between the units and systems of units causes confusion even to the professionals in the field.

It is important to realise that we are all subject to radiation exposure just by living on Earth. To illustrate doses more clearly John used the “Banana Equivalent Dose” table, using bananas because they are a natural source of radioactive isotopes. Eating one banana is the same as 0.1 µSv. exposure. It must be stated that this is an unconventional comparison and frowned upon by experts.

Bananas Equivalent exposure

1 - 100 Yearly dose from living near a nuclear power station 50 Having a dental x-ray 100 Average background dose per day 400 A single flight from London to New York 700 Living in a stone, concrete or brick building per year 200 - 1000 Chest x-ray 100,000,000 Fatal dose with death within two weeks

There is a story from America that following the destruction of the Twin Towers, the military began to check all ships incoming to ports around the States for the possibility of hidden atomic devices only to find that a number of ships that had been rounded up in the Gulf of Mexico because radioactivity had been detected aboard turned out to be banana boats.

At ground level from all sources, we receive on average 2.6 mSv per year. Then we looked at Cosmic Rays and were told that at ground level they make up about 10% of our yearly radiation dose at about 0.2 mSv; at an altitude of 12 km it is 20 mSv and at 350 km and on the ISS, it is 150 mSv but in Deep Space it is between 400 – 1000 mSv.

Most of our cosmic rays come from coronal mass ejections from the Sun. Galactic Cosmic Radiation (GCR) comes from outside the Solar System where it is thought the source is mainly from the massive magnetic fields produced by Supernovae. John explained that it is believed atoms and their surrounding electrons are accelerated to almost the speed of light. Although the majority of GCR comprises of Hydrogen and Helium atoms there is a significant contribution from the heavier elements of the periodic table.

We were told that luckily, we on Earth are protected by the Magnetosphere which diverts most of these particles away.

John now turned to radiation doses received during space travel. He said that the Apollo missions weren’t exposed to particularly high dose rates but a trip to Mars could reach a total exposure of about 1,200 mSv including 18 months on the surface, which is getting close to the maximum dose allowed for an astronaut in his or her lifetime.

It will be necessary, for the health of the crew, to reduce the radiation dose received during a space mission; one way would be to get there faster.

It would also be necessary to improve the model of radiation damage that is used today which is based mainly on the evidence from the survivors from Hiroshima and Nagasaki, which shows the amount of radiation received against the chance of death and graphically is a straight line. More recently the line has been projected down to zero still keeping it as a straight line and this is currently the model in use.

There is some evidence that low doses of radiation are far less dangerous than predicted and, in some cases, even beneficial and don’t follow the straight line. In radiation protection circles this is a contentious issue.

John talked about ways of protecting astronauts from radiation during space missions and said that materials with a high hydrogen content, such as plastics which are used currently, reduce the dose by as much as 30 to 40%. There is also research being done with electrostatic and magnetic shielding to deflect the radiation.

We were told that, surprisingly, concrete is very good at stopping cosmic radiation but rather difficult to launch…

There is also research being carried out on dietary supplements which promote the body’s natural defences as an additional way of protecting astronauts. Another way of helping to protect the crew is to choose a route that avoids Coronal Mass Ejections and even find a path that uses existing stellar magnetic fields to deflect radiation.

Once on the surface, there are weak magnetic fields which would be better locations to put a base, but if possible, living underground would solve many problems.

John told us that he and his 4-year old grandson were planning to go to the Moon and in discussing the trip he said they would have to avoid all that radiation from the Sun to which his grandson suggested going at night because you could still the see the Moon. Sadly, there was another problem because Sid the cat who was to be their pilot, died.

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Following a ten-minute break, Jan Drozd gave a fascinating and light-hearted talk about astrology.

The Pseudoscience of Astrology Jan Drozd

Jan appeared to give his presentation wearing the hat of an ancient astrologer and offering to give predictions but then countered it by saying before he began that from a scientific perspective astrology is a complete load of rubbish. Many cultures practiced astrology and many still believe in it today; in America at least 25% of the population still do.

Babylonians used to look at the entrails of dead animals to see what predictions they could make from them.

Jan said he wanted to talk about Western astrology and to show how in the past astrology and astronomy were considered together. Babylonia priest astrologers-astronomers tried to make predictions from the stars and planets. Stone tablets dating from about 700 BC show quite accurately and without access to modern astronomical aids to help them, the rising and setting times of Venus which was essential to their predictions. They developed the use of the sexagesimal system we use today for a circle with 360o and the hour divided into 60 minutes and minutes into 60 seconds.

The Ecliptic, the apparent path of the Sun in a year, was very important to the Babylonians in their astrology – astronomy.

The Celestial Sphere Showing the Ecliptic which was so important to the Babylonians

The planets and the Moon also follow a similar path, all within a narrow band of between 8o and 9o north or south of the ecliptic and this band is known as the Zodiac.

Jan showed an image of part of the night sky as it was 45 minutes before sunrise in January the 30th, 2016 from Minneapolis, USA, conveniently showing the five most visible planets.

In this image are the five planets that were those known to the Babylonians.

The Babylonians divided the zodiac into twelve equal zones each 30o wide which was the first celestial co-ordinate system. Each of these zones was named after the constellation the Sun appeared to be in, starting with the Sun’s position at the Vernal Equinox.

Jan wondered how the Babylonians had been able to identify when the Equinox occurred. One way would have been to observe the point where the Sun rose each day during the year. At the winter solstice it rises as far south as it is going to rise, then at the Summer

3 solstice it would have appeared as far north as it is going to appear and exactly midway between the two is the Vernal equinox which would be due east, setting due west.

We were told that 12 zones were used because there were 12 months in the year although there are really 13 constellations, so they conveniently left out Ophiuchus.

One way we can see what constellation the Sun appears in is to look towards the eastern horizon just before sunrise when the sky is still just dark enough to recognise the pattern of stars.

Jan also said that due to precession there is now a distinction between zodiacal constellations and the zodiacal signs. The start had been in the constellation of Aquarius looking from the Earth but precession had moved that point into Pisces as we see it today. Tell this to today’s astrologers and they just shrug their shoulders.

Looking back at the historical development of astrology, the Babylonians were concerned about omens and this belief passed to others. The Greeks were very interested and Ptolemy (around AD 100 to 170) wrote a number of books on both astronomy and astrology. He laid down the basis of Western astrology which became very influential.

In 1627 Johannes Kepler published a very accurate star catalogue developed mainly to help improve astrological predictions. A lot of Kepler’s work was based upon the data produced by Tycho Brahe. Jan said that at least 800 horoscopes made by Kepler still exist today.

Galileo also produced a lot of astrological predictions which gave him widespread recognition and gave him a good income.

Jan said that many consider the publication of Isaac Newton’s ‘Principia Mathematica” in 1687 to be the first major work of Enlightenment. From the early 1700s intellectuals began to dismiss astrology and in the latter half of the 17th century, astronomy became an established independent scientific discipline.

Today, the horoscopes we read in the newspapers are based on a simplified version of astrology which Jan declared absolute rubbish but great fun for some.

He finished by mentioning a number of books by Erich Van Daniken where all the scientific evidence was against him yet they were still best sellers. But he did talk about one book called “A Scheme of Heaven and the Birth of Science” by Alexander Boxer that gives a lot of detail about the history and other aspects of astrology.

To close the Zoom meeting, Brian Mills said that next month our own John Wayte will be giving a presentation he calls “The Moon’s Visitors”. Members should receive an invitation with details of how to join the next Zoom meeting before it takes place on Wednesday the 15th of July.

FUTURE PROGRAMME OF WAS ZOOM MEETINGS

Details of future meetings can also be found on our brand-new website at: www.wadhurstastro.co.uk.

August 12, 2020 – (This will be the first time we will be having a meeting in August) The World Renowned astro-imager, Nik Szymanek, talks to us about “Astronomical Photography for Beginners”, followed by a short talk by Mike Cobourne, entitled “Cathedrals as Solar Observatories and Sundials”

September 16, 2020 – Dr David Whitehouse returns with a talk based on his latest book; “Space 2069”. This will be followed by the Sky Notes given by Brian Mills.

October 21, 2020 – We are “Celebrating 30 years of the Hubble Space Telescope” courtesy of Dr Stephen Wilkins.

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JOHN WAYTE’S SCIENTIFIC TITBITS

Weird green glow spotted in atmosphere of Mars

Artist's illustration of the European Space Agency's ExoMars Trace Gas Orbiter detecting the green glow of oxygen in the Martian atmosphere. (Image: © ESA)

The atmosphere of Mars has a distinct green glow, just like Earth's.

The European Space Agency's Trace Gas Orbiter (TGO) spotted an emerald glow in Mars' wispy atmosphere, marking the first time the phenomenon has been spotted on a world beyond Earth, a new study reports. "One of the brightest emissions seen on Earth stems from night glow. More specifically, from oxygen atoms emitting a particular wavelength of light that has never been seen around another planet," it was said in a statement by lead author Jean-Claude Gérard. "However, this emission has been predicted to exist at Mars for around 40 years — and, thanks to TGO, we’ve found it,"

In this image, taken by astronauts aboard the International Space Station (ISS) in 2011, a green band of oxygen glow is visible over Earth's curve (Image credit: NASA)

As Gérard noted, the green emission is characteristic of oxygen. Sky watchers at high latitudes here on Earth can see this signature in the ethereal multi-coloured displays known as the auroras, which are generated by charged particles from the Sun slamming into molecules high up in our atmosphere.

But night glow is different. It's caused by the interaction of sunlight with atoms and molecules in the air, which generate a subtle but continuous light. This emission is hard to see, even here on Earth; observers often need an edge-on perspective to make it out, which is why some of the best images of our planet's green night glow come courtesy of astronauts aboard the ISS. Day-glow, the diurnal component of this constant emission, is even harder to spot. And it's driven by a slightly different mechanism.

5 "Previous observations hadn't captured any kind of green glow at Mars, so we decided to re-orientate the UVIS nadir channel to point at the 'edge' of the Mars atmosphere similar to the perspective you see in images of Earth taken from the ISS." The team scanned the Martian atmosphere at altitudes between 12 miles and 250 miles (20 to 400 kilometers). They found the green oxygen glow at all heights, though it was strongest around 50 miles (80 km) up and varied with the Red Planet's distance from the Sun.

“Night-glow occurs as broken-apart molecules recombine, whereas day glow arises when the Sun's light directly excites atoms and molecules such as nitrogen and oxygen" European Space Agency (ESA) officials wrote in the same statement.

Gérard and his colleagues used TGO's Nadir and Occultation for Mars Discovery (NOMAD) instrument suite, which includes the Ultraviolet and Visible Spectrometer (UVIS), to study the Red Planet's air in a special observing mode from April through to December last year.

"The observations at Mars agree with previous theoretical models, but not with the actual glowing we've spotted around Earth, where the visible emission is far weaker," Gérard said. "This suggests we have more to learn about how oxygen atoms behave, which is hugely important for our understanding of atomic and quantum physics."

TGO has been circling Mars since October 2016. The orbiter is part of the two-phase European-Russian ExoMars programme, which plans to launch a life-hunting rover called Rosalind Franklin, toward the Red Planet in 2022.

The Rosalind Franklin was originally supposed to lift off this summer, but technical issues with the spacecraft's parachute and other systems caused the mission to miss that window.

Credit Space.com

Solar Orbiter spacecraft makes its first flyby of the Sun

An artist's depiction of the joint NASA- ESA Solar Orbiter at work studying the Sun.

(Image: © ESA/Medialab)

Solar Orbiter, a joint mission by NASA and the European Space Agency, has hit the first big milestone of its Sun-watching mission — and the spacecraft will soon have pictures to prove it.

The probe is designed to give scientists a view of our Sun unlike any they've ever seen before. That's because Solar Orbiter carries technology to gather images of our star, and its trajectory will allow it to study the poles of the Sun, which never align toward Earth. And the science starts now, with the spacecraft executing its first flyby of the Sun, or perihelion, today (June 15). The orbital maneuver brought the probe to about half the distance between the Earth and the Sun, or about 48 million miles (77 million kilometres).

"We have never taken pictures of the Sun from a closer distance than this," said Daniel Müller, ESA's Solar Orbiter project scientist. LAY SOUND According to the statement, the spacecraft's first imaging campaign will occur in the week following this close approach. It will take the spacecraft another week to beam those images back to Earth given its current distance from home, and the mission team expects to publish the resulting images in mid-July.

NASA's Parker Solar Probe is already flying several times closer to the sun than Solar Orbiter, but that spacecraft is not equipped to photograph the Sun; instead it observes its immediate surroundings.

Solar Orbiter was launched in February and carries a total of 10 instruments: six telescopes and four instruments designed to study the spacecraft's immediate surroundings. Mission team members have been powering up and checking each instrument since shortly after the spacecraft’s launch, but this week's data-gathering will be a new test for the probe.

6 "For the first time, we will be able to put together the images from all our telescopes and see how they take complementary data of the various parts of the Sun, including the surface, the outer atmosphere or corona, and the wider heliosphere around it" Müller said.

And although scientists are excited about receiving these images, the spacecraft hasn't yet begun its main science work. It will complete another perihelion early next year; the first perihelion of its main science campaign will occur in early 2022.

Credit Space.com

John Wayte

THE HISTORICAL INDIAN CONTRIBUTION TO ASTRONOMY Part 2 Jan Drozd

Turning to astronomy, the first recorded idea that the Earth is moving and the Sun is at the centre of the Solar System (heliocentric system) is found in several ancient Vedic Sanskrit texts. Part of a Vedic tradition was to use related astronomical, mathematical and geometrical concepts in some religious rituals and altar designs. Yajnavalkya (c. 9th– 8th century BC) recognized that the Earth is spherical and believed that the Sun was "the centre of the spheres". He also recognized that the Sun was much larger than the Earth, which would have influenced this early heliocentric concept. Amazingly, he somehow also calculated the relative distances of the Sun and the Moon from the Earth as 108 times the diameters of these heavenly bodies, close to the modern measurements of an average of 107.5 for the Sun and 110.6 for the Moon.

As in other cultures of the time, early Indian astronomy was closely intertwined with religion and what we call astrology.

Indian astronomy flowered in the 6th century under Aryabhata (AD 476-550) and Brahmagupta (AD 598-668) who developed a rigorous mathematical approach. It influenced Islamic and Chinese astronomy and was in advance of Western European astronomy of the time.

Aryabhata, in his major work, Aryabhatiya, written around AD 510, used a geocentric (Earth centred) model with epicycles, in which the Earth was taken to be spinning on its axis. The latter was a millennium before Copernicus proposed the same. He also deduced that the Earth was spherical. It is a matter of debate whether certain aspects of Aryabhata's model suggest he may have had some thoughts about a heliocentric system. Amongst his many other achievements, he was also the first to deduce that the light from the Moon and the planets was reflected from the Sun and he believed that the planets followed elliptical orbits. He accurately calculated many astronomical constants, such as the times of the solar and lunar eclipses. Considered in modern English units of time, Aryabhata calculated the sidereal rotation (the rotation of the Earth referencing the fixed stars) as 23 hours, 56 minutes, and 4.1 seconds; the modern value is 23:56:4.091. In mathematics, his definitions of sine, cosine and related functions, influenced the development of trigonometry, especially in the Islamic world. He also played an important role in developing the Hindu-Arabic numeral system (described above).

Arabic translations of Aryabhata's Aryabhatiya were available from the 8th century, while Latin translations were available from the 13th century, before Copernicus had written De revolutionibus orbium coelestium (published in 1543), so it is possible that Aryabhata's work had an influence on Copernicus's ideas.

Bhaskara (1114– 1185) expanded on earlier models in his astronomical treatise Siddhanta-Shiromani. Amongst many things, he accurately defined many astronomical quantities, including, for example, the length of the sidereal year, the time that is required for the Earth to orbit the Sun, as approximately 365.2588 days. The modern accepted measurement is 365.25636 days, a difference of just 3.5 minutes. He was a pioneer in some of the principles of differential calculus and their application to astronomical problems. In this, his work predates some of that of Newton (1642-1726/7) and Leibniz (1646-1716), often considered the originators of calculus, by over half a millennium.

Many other early Indian astronomers made contributions. For example, Brahmagupta (598-668) in addition to his pioneering mathematical work on the use of the number zero (described in part 1- see the June newsletter), like Varahamihira (505 – 587), thought that it was the nature of the Earth to attract bodies, which some see as the first recognition of the force of gravity.

The Kerala School of Astronomy and Mathematics which flourished between the 14th and 16th centuries, in attempting to solve astronomical problems developed a number of important mathematical concepts. However, there is no evidence that this work was known beyond India, or even outside of Kerala, until the nineteenth century.

However, as in the North African and Middle Eastern Islamic Empire, there was no later Scientific Revolution as there was in Western Europe from the time of Copernicus (1473-1543) onwards.

At the beginning of the 18th century, the Mahārāja of Jaipur, Sawai Jai Singh (1688–1743), constructed several large astronomical observatories, which contained large instruments to accurately determine, by naked eye (no telescopes were used), the position of celestial objects for astronomical tables. Their contribution to astronomy outside of India was minimal. The observatory at Jaipur is a major tourist attraction.

7 Jantar Mantar Observatory, Jaipur Built in 1730 McKay Savage

Many more recent Indian astronomers and other scientists have made major contributions, probably the most famous are:

Meghnad Saha (1893 – 1956) was an Indian astrophysicist who gained global prominence for his development of the Saha Ionization Equation, used to describe chemical and physical conditions in stars. His work allowed astronomers to accurately relate the spectral classes of stars to their actual temperatures He was nominated several times for the Nobel Prize in Physics

Satyendra Nath Bose (1894 – 1974) was a theoretical physicist whose work had an influence on fundamental theoretical astrophysics. He is best known for his work on quantum mechanics in the early 1920s, providing the foundation for Bose–Einstein statistics and the theory of the Bose–Einstein condensate. The class of particles that obey Bose–Einstein statistics, bosons, was named after Bose. Many in the field thought he was worthy of a Nobel Prize.

Subrahmanyan Chandrasekhar (1910 – 1995) was an astrophysicist of Indian origin. He was awarded the 1983 Nobel Prize for Physics with William A. Fowler for theoretical studies of the physical processes of importance to the structure and evolution of the stars. His mathematical treatment of stellar evolution yielded many of the current theoretical models of the later evolutionary stages of massive stars and black holes. The Chandrasekhar limit is named after him.

Subrahmanyan Chandrasekhar, astrophysicist. The Chandrasekhar Limit, the maximum limit of a stable White Dwarf, is named after him. NASA

Vikram Sarabhai (1919-1971) was an Indian physicist and astronomer who is considered as the father of India’s space programme.

Having researched and written this article, I feel that the Indian contribution to astronomy and especially to supporting mathematics, has often been underestimated.

Now, as I am feeling hungry after finalising this article, I think I will go and order a meal to be delivered from my excellent local Indian restaurant to have with a beer (or two)! When I get the bill, I will reflect on the origin of any zeros in it!

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THE SKY NOTES FOR JULY

Planets

Mercury is at inferior conjunction on the first day of the month which means it lies almost exactly between the Sun and the Earth. Following this it moves to the west of the Sun to become a morning object visible low down in the east-north-east shortly before sunrise. It travels swiftly westwards until by July 22nd (the date of greatest western elongation) it lies 20° from the Sun and rises an hour and a half ahead of it. At the time of sunrise, the planet will be 12° high where it shines at magnitude +0.3. If, however, you wait until the last day of the month Mercury will have brightened considerably to −0.8 and will still be at a similar altitude at sunrise amongst the stars of Gemini. Its position on the 22nd and 31st is shown in fig 1. The constellations shown are correct for the 22nd only but will, of course, be invisible by sunrise anyway.

Venus is a stunning morning object shining at magnitude −4.5 early in the month thanks to its proximity to Earth. The planets phase (a waxing crescent) is compensated for by its apparent angular diameter which at the start of July is over 40ʺ (40 arc seconds). Venus is moving away from the Sun and gaining in altitude although its declination remains fairly constant. Fig 1 shows how its height above the eastern horizon increases throughout the course of the month. If you are about during the very early hours of the 11th, Venus will pass one degree to the north of the bright star Aldebaran in Taurus.

Earth reaches aphelion on July 4th at 12:56 BST. This is when, in our yearly orbit, we reach the point where we are furthest from the Sun. At that time, we will be 152,095,296 km from our parent star which equates to 1.02 AU (1.02 astronomical units). As I have said before the variation in the distance of the Earth from the Sun has only the tiniest effect on temperature: it is the tilt of our planet’s axis that brings about the seasons and with it their associated temperature changes.

Mars is still a morning object, rising as it does a little before 01:00 at the beginning of July although by the end it becomes visible just after 23:00 very low down in the east. Despite this it is currently best observed in the early hours and before dawn. The red planet’s magnitude is now in negative numbers rising from −0.5 to −1.0 during July as its disk grows from 11.4ʺ to 14.3ʺ as the October opposition draws closer. Mars begins the month in Pisces moving eastwards into Cetus on the 8th before re-entering Pisces on the 26th. A waning gibbous Moon is 3° south east of Mars on the 12th. Fig 2 shows the location of Mars at 01:00 around the middle of the month.

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Jupiter is now an evening object becoming visible in the south east just after 22:00 at the start of the month. The planet comes to opposition on the 14th when it is at its (approximate) closest to Earth and therefore at its largest and brightest. The gas giant’s disk measures 47.6ʺ across the equator and shines at magnitude −2.7. It is visible throughout the hours of darkness rising as the Sun sets and then setting itself at sunrise. On the night of opposition, it culminates (crosses the meridian due south) at 01.00BST at a rather disappointing altitude of 17°. It is currently found amongst the stars of Sagittarius, moving retrograde, which continues until mid September. Now is a good time to follow the motions of the four Galilean moons as they circle the planet. A pair of binoculars are all you need providing you are able to mount them on a tripod or find another way of keeping them steady. With a moderately sized telescope, you will be able to see the more obvious cloud belts on the planet and with luck the great red spot which incidentally has been shrinking lately. Below are some of the more convenient times for when the spot transits the planet’s central meridian. Obviously, it is visible for some time either side of this although you should bear in mind that Jupiter completes one revolution in just under 10 hours. Figs 2 and 3 show the position of Jupiter at different times around the middle of the month.

Date Transit Time Date Transit Time Date Transit Time July 4th 00:48 July 15th 23:59 July 27th 23:53 July 8th 23:15 July 20th 23:07 July 30th 21:22 July 11th 00:53 July 23rd 00:45 July 13th 22:22 July 25th 22:15

Saturn is also an evening object rising around 20 minutes after Jupiter that lies just 6° to the west. Like its slightly larger neighbour it also reaches opposition in July although in the case of Saturn this occurs on the 20th. The similarity ends there because whilst Jupiter shines beacon- like Saturn (although obvious) appears far more like a moderately bright star to the naked eye. Its brightness doesn’t quite reach negative numbers peaking at magnitude +0.1 whilst size - wise, if you include the rings, then it is more on a par at 41.9ʺ. The disk of the planet, for comparison, is 18.5ʺ. Saturn crosses the meridian on July 20th at just after 01:00 with an altitude of 18°. The planets brightest Moon, Titan at magnitude +8.2, is best seen to the west of Saturn on the 12th and 28th and to the east on the 4th/5th and 20th/21st. Saturn begins the month in Capricorn but moves retrograde into Sagittarius on July 3rd where it remains during opposition. The planets north pole is still tilted towards Earth and that angle is increasing to slightly improve our view of the upper surface of the ring system. Figs 2 and 3 show the position of Saturn in the middle of the month at 01:00 and 22:30 respectively.

Both of the gas giants suffer from low altitude thanks to their current negative declinations: Jupiter at −22° and Saturn at −20°. This is a measure of how far below the celestial equator (which is 0° and is the Earth’s equator projected out into space) they are but don’t forget that the celestial equator itself is only 39° above the horizon from our part of the UK when looking due south. With that in mind you can see that from our location we are not ideally situated to observe objects that are a considerable distance below the celestial equator. So, it follows that an astronomical body whose declination is positive will be seen far better because it will be higher in the sky, be visible for longer (describes a longer arc) and suffers less from atmospheric disturbance that reduces the further from the horizon that you ascend. As an example, let’s take the star Deneb in Cygnus whose declination is +45° which doesn’t make it sound as if it is likely to be especially high in the sky. However, at the end of September it is on the meridian, due south at 21:00 with an altitude of 84° which is just 6° from the zenith (overhead point). We arrive at this figure because we already said that the celestial equator crosses the meridian at a height of 39° so if we add the declination of Deneb to that we arrive at the above answer: 39° + 45° = 84°.

If you’re wondering why the altitude of the celestial equator due south is 39° it is because 90°−51° (our latitude) =39°. If you were standing on the equator then the celestial equator would run from the east to the west cardinal point and would pass overhead through the zenith. If, however you were standing on one of the Earth’s poles then the celestial equator would run around the horizon. Therefore, the height of the celestial equator is a function of your latitude wherever you happen to be.

The planets Jupiter and Saturn move comparatively slowly, due to their much larger distances from the Sun, so any change in their position along the ecliptic will be gradual. After this year’s opposition Jupiter’s declination becomes less and less negative until by 10 2024 it is +22° which means it will be 61° in altitude when it culminates at opposition (22° + 39° = 61°). Saturn’s negative declination also decreases but far more slowly due to it being even further from the Sun and hence its movement is slower.

Lunar Occultations In the table below I’ve listed events for stars down to magnitude +7.5 that mostly occur before midnight although there are many others that are either of fainter stars or occur at more unsociable hours. DD = disappearance at the dark limb, RD = reappearance at the dark limb and RB = reappearance at the bright limb. The column headed “mm” (millimetres) shows the minimum aperture telescope required for each event.

July Time BST Star Mag Phase % illumination mm July 22nd 21:52 ZC1479 6.4 DD 6 80 July 28th 22:07 ZC2209 5.6 DD 65 40 July 31st 21:27 ZC2659 6.2 DD 91 80 July 31st 23:05 M28 Globular cluster 6.9 DD 92 110

Phases of the Moon for July

Full Last ¼ New First ¼ July 5th July 12th July 20th July 27th

Penumbral Lunar Eclipse During the early hours of July 5th, the northern portion of the Moon will pass through the penumbral section of the Earth’s shadow just before it sets. First contact occurs at 04:07 when the Moon is just 4° above the south western horizon. The Moon sets just 30 minutes later.

As mentioned last month it is unlikely that you would notice any variations in lunar brightness during a penumbral eclipse. I was able to observe the Moon very soon after it rose during a similar event on June 5th and was unable to distinguish any difference in illumination between the northern and southern parts of the Moon. Given the time of day and position of the Moon I think it highly unlikely that many observations will be made on this particular occasion.

ISS Below are details for the evening passes of the International Space Station (ISS) this month. The details of other passes, including those visible between midnight and dawn, can be found at www.heavens-above.com. Please remember that the times and directions shown below are for when the ISS is at its maximum elevation, so you should go out and look at least five minutes beforehand.

July Time Mag. Alt° Az. July Time Mag. Alt° Az. 12th 23:59:03 -3.3 39° SSE 22nd 22:24:02 -3.6 78° N 13th 23:11:01 -2.9 28° SSE 23rd 21:35:46 -3.6 80° N 14th 23:59:23 -3.9 68° SSE 23rd 23:12:34 -3.9 77° SSW 15th 23:11:16 -3.7 52° SSE 24th 22:24:18 -3.8 89° NNW 16th 22:23:09 -3.3 38° SSE 25th 21:36:01 -3.7 81° N 16th 23:59:47 -3.8 86° N 25th 23:12:42 -3.4 46° SSW 17th 23:11:36 -3.9 82° SSE 26th 22:24:28 -3.7 62° SSW 18th 22:23:24 -3.8 67° SSE 27th 21:36:13 -3.8 79° SSW 19th 23:11:57 -3.7 80° N 28th 22:24:29 -2.8 35° SSW 20th 22:23:43 -3.7 87° N 29th 21:36:15 -3.3 48° SSW 21st 23:12:18 -3.7 82° N

Meteors – The Perseids One of the year’s most active showers, the Perseids, begins on July 17th and continues until August 24th with maximum activity expected in the afternoon of August 12th. I’ll talk about it more in the next Newsletter but for now we can expect the shower to start slowly and very gradually ramp up. The sky should be dark enough by 23:00 at the beginning of the period when the Sun will be 12° below the horizon (end of nautical twilight). As the month moves on the Sun sets progressively earlier until on the last day of July it reaches a position 18° below the horizon a little before midnight. That is when it will be astronomically dark. That’s all very well but moonlight will interfere, from around the 25th when the Moon will be low in the west at 23:00. On July 31st it is approaching full and almost due south, again at 23:00. The only saving grace is that because of the position of the ecliptic at this time of year it will always be reasonably close to the horizon. Things do improve for the night of maximum on the 12th/13th August with a waning crescent Moon rising shortly after midnight. The meteors themselves are fast, travelling at around 60km/s, very often leaving a short-lived ionised train behind them.

The Night Sky in July (Written for 22.00hrs BST mid month) As the month begins we still have astronomical twilight throughout the night i.e. the Sun never reaches 18° below the horizon. However, by the middle of July, the 19th to be precise, the centre of the Sun achieves that negative altitude and true darkness returns, if fleetingly at first.

In the east all three members of the Summer Triangle are well placed with the brilliant Vega now 65° in altitude. It does depend on the time that you observe it but I’ve always thought it would be more appropriate to label it the “Autumn Triangle”. Deneb, in Cygnus,

11 is the faintest of the trio and marks the tail of the celestial swan whilst at the other end of the bird’s body Albireo, that easy on the eye double star whose components are revealed in a small telescope as yellow and blue, indicates the head. The Milky Way runs along the length of Cygnus although it will be better seen if you wait until the end of the month when astronomical darkness will have returned before midnight. Below Cygnus the square of Pegasus is almost clear of the horizon bringing with it Andromeda and, of course, the galaxy M31 now 15° high in the north east. From a point almost exactly due east a line of small and faint constellations reaches northwards. They are from the horizon up Equuleus (the pony), Delphinus (the dolphin), Sagitta (the arrow) and finally Vulpecula (the fox) the last of which lies just below previously mentioned Albireo.

Turning to the south we find Hercules high up on the meridian with one of his globular clusters, M92, just 10° from the zenith. Its magnitude is +6.3 and is sometimes quoted as being visible to the naked eye although location and sky conditions would have to be exceptional for that to really be the case. It is an old cluster whose age is thought to be between 10 and 12 billion years. Messier 13, 10° away but still in Hercules has always overshadowed its fainter rival and at magnitude +5.8 there is a marginally better chance of seeing it unaided. Although both these clusters bear Messier designations neither was discovered by the French astronomer: he just added them to his growing catalogue of objects to be aware of whilst comet hunting. M92 was initially recorded by Johann Bode in 1777 whilst M13 was first observed by Edmund Halley in 1714. Directly below the strong man is the sprawling constellation of Ophiuchus that bisects the sea serpent in two whilst below that Scorpio is hugging the horizon.

Towards the west Cancer is just setting soon to be followed by the celestial lion. A little higher we find Boӧtes and the bright star Arcturus still at an altitude of 45° and to their west are the two small groups of Coma Berenices and Canes Venatici the former of which hosts the north galactic pole.

Towards the north we find that Ursa Major is descending on the west side of the meridian whilst Cassiopeia and Cepheus are ascending on the east side. If you look low down you should be able to see the bright star Capella, in Auriga, which is circumpolar from our part of the UK where it remains at least 7° above the horizon. If you have never identified all the twists and turns of Draco then now would be a good time to make good that omission as it straddles the meridian close to the zenith.

Highlights for August 2020 August 12th/13th – Perseid maximum August 13th – Venus at greatest western elongation (morning object)

Brian Mills FRAS

CAMBRIDGE UNIVERSITY TALKS FOR CHILDREN

Jan Drozd reminds us that the talks on astronomy for children by Cambridge University are continuing and there are more in the series. The links are: https://www.public.ast.cam.ac.uk/online-astronomy-activities-1 https://www.youtube.com/channel/UCa7e55mYI2xQAoV_0hRmL-g

CONTACTS

General email address to contact the Committee [email protected]

Chairman - Brian Mills FRAS 01732 832691

Secretary - Phil Berry 01580 291312

Treasurer - John Lutkin

Membership Secretary - John Wayte

Newsletter Editor - Geoff Rathbone 01959 524727

Observing Director - Ian McCartney

Librarian - Phil Berry

Catering Manager - Jim Cooper

SAGAS Representative - Eric Gibson

Wadhurst Astronomical Society website: www.wadhurstastro.co.uk

SAGAS website: www.sagasonline.org.uk

Any material for inclusion in the August 2020 Newsletter should be with the Editor by July 28th 2020

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