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Dr Nick Lomb: This is a guide to the night sky in July. My name is Nick Lomb; I’m curator of astronomy for Sydney Observatory and Powerhouse Museum. You can find this podcast on the Sydney Observatory blog, www.sydneyobservatory.com/blog.

If you’d like to become familiar with the night sky, what you need to do is download the map associated with this podcast; it’s simple to download on PDF. Print it out and take it outside with you. Dress warmly, because in July the nights or evenings tend to be fairly cool. What you also need is some kind of torchlight and preferably a red torchlight, because red does not destroy your adaptation to the night sky. So, you can look at the map and also look up into the night sky.

You also need to be familiar with the cardinal directions, that is, north, west, south and east. So, you need to know where they are with respect to your location. East is, of course, where the Sun rises; west is where the Sun sets. So, that gives you a fairly good indication. And, north is the direction of the Sun around the middle of the day. Around 12 noon, the Sun is roughly due north.

So, let us start our tour of the night sky in July. And let us start in the east, where we can see the familiar sight of the constellation of Scorpius, the scorpion. This is a very welcome sight, visible in the Australian winter; it’s a very obvious constellation. It’s one of the really few bright and easy to find constellations, so it is an excellent signpost to the night sky. It’s a long, curving line of bright stars. This time of the year, it’s in the eastern sky with the claws of the scorpion high up, a little bit towards the north. The actual sting, or tail, of the scorpion is towards the south.

In the middle of the scorpion, we find a reddish star, Antares, and that of course represents the heart of the scorpion. Antares is a huge star; it’s a giant star. Its name, Antares, means the rival of Mars. The reason for the name is because Antares has a similar, reddish colour to the planet Mars. So, occasionally, when Mars passes close by which it does, as Antares is very close to the ecliptic, the line on which the planets move across the sky then they look like two very similar reddish objects, close together in the night sky. It’s a very spectacular sight when that happens.

As I said, Antares is a giant star. It is relatively cool. Its surface temperature is about 3,200° Celsius, which seems hot. But, compared to our own Sun, which has a temperature around 5,500° C, it is a relatively cool star. It is that coolness that gives it the red colour.

But because it’s so big, so huge, even though it’s relatively cool, it still puts out a huge amount of light. So, it still appears to be a very bright star, even though it is 600 light years from us. Light has taken us 600 years to reach us from Antares.

It is so large that if we replaced our own Sun by Antares and you wouldn’t want that to happen then the Earth would be engulfed by it, as would the planet Mars and many of the asteroids the rocky objects that circle the Sun between the orbits of Mars and Jupiter. Jupiter would be outside Antares, but not very far from it. So, the solar system would be a very different place. Certainly, it would no longer be a hospitable place for us, if Antares replaced the Sun.

Antares has a companion star, circling around it. It’s a very hot star, so it’s quite a contrast. It’s a star with a temperature around 18,000° C. It’s a bluish star. If people look at the two of them together, the reddish Antares and the blue companion star, they sometimes describe the companion star as green. That seems to be some kind of contrast effect in our eyes.

This companion star appears small, compared to huge Antares, but it is actually larger than our own Sun. It’s something like four times wider than our own Sun and 10 times the mass of our own Sun. It’s something like 2,000 times as bright as our own Sun. We don’t know how long the companion star takes to circle around Antares, but it is believed to be something like about 1,000 years.

Now, let us move from the eastern part of the sky, from Scorpius the scorpion to the north. So, we’re facing north and looking up. The most obvious star that we see is a star called Arcturus. This is part of the constellation of Boötes, which is the herdsman. Arcturus means ‘bear watcher’.

It’s one of the brightest stars in the sky; the fourth brightest star in the sky. It is the brightest star in the Northern Hemisphere, as seen from the Northern Hemisphere. It’s a slightly orange coloured star, and it’s 37 light years from us. So, it is far closer than Antares, which as you will recall, is 600 light years away. But, just like Antares, it appears like a bright star in the sky.

It’s an interesting star for a variety of reasons. One of them is that it moves around the centre of our galaxy a little bit slower than our own star, the Sun. And, of course, we move around together with the Sun. It’s believed to be a somewhat older star than our own Sun. It comes from an older generation of stars in the galaxy.

There has been a suggestion which may or may not be true, but it’s intriguing that it does not come from our own galaxy, but comes from a small galaxy that merged with our own galaxy many thousands of millions of years ago. So, that’s why it has a different motion to other stars within this part of the galaxy. It’s moving a little bit more slowly around the centre of the galaxy.

Let us move now to face west. The most obvious star we can see is a star called Regulus. That is west and a little bit towards the right, a little bit towards the north. So, it’s in the north-west. It’s a star called Regulus, and the name Regulus means ‘little king’. It’s 77 light years away. It gives off more than 100 times as much light, or at least if we were close to the star, we would see that it intrinsically gives off something like 100 times as much light, as our own Sun. It’s a fairly hot star, 12,000° C which compares with, if you recall, our own Sun at about 5,500°C.

It’s a star which is right on the ecliptic, right on the path of the planets and the Sun and the Moon as they move along across the sky, which means that sometimes the Moon appears to pass right on top of Regulus. The Moon can thus move in front of Regulus and so it’s a star that is often occulted by the Moon.

Regulus also has a companion star circling a round it, but it’s a fairly low mass star that is quite a large distance away from Regulus. In fact, this companion is 4,000 times as far away from Regulus as the Earth is from the Sun. This large distance means that it circles around Regulus, the main star of Regulus, very slowly. It’s believed that it would take at least 100,000 years for this companion star of Regulus to circle around Regulus.

I’m afraid none of us are going to be around to see it complete an orbit, but people in the distant future will be able to actually measure the exact period. But for the moment all we can estimate is that it would take somewhere over 100,000 years. Interestingly this companion star, this little companion star that’s circling around Regulus, is also a double star. The two stars of the companion take about 1,000 years to circle around each other.

Let us move now to the southern part of the sky. So we face south and look up and what we see, at least in the early evening, high up we can see the Southern Cross. This is the best time to look at the Southern Cross, the famous group of stars in the Southern Hemisphere. It’s the best time to view it in the early evening because it’s very high up in the sky, and it’s sort of standing vertically due south at this time of the year in the early evening.

If you look at Southern Cross you can easily see four stars. There’s also a fifth star which sadly is becoming lost due to light pollution in our cities. If you are looking at the Southern Cross from a dark sky in the country, it’s nice and prominent. But if you look at if from a suburb of a major city, whether it’s Sydney or Melbourne or Adelaide or Perth, then the fifth star in the Southern Cross is getting hard to see.

The bottom star of the Southern Cross, at least at this time of the year, is a star that we call Acrux, or alternatively Alpha Crucis. That is the brightest star of the Southern Cross. If you look at Acrux with a small telescope, you can see that it’s actually a double star, two stars. In fact, there’s a third star nearby as well. They are about 320 light years from us. So the light that we see today left Acrux 320 years ago.

Going clockwise, the star on the left is a star called Beta Crucis, or, it has a proper name, Mimosa. That is the second brightest star in the Southern Cross. That’s a fairly hot star at about 350 light years distance from us. It’s important to note that stars that appear close together in the sky, like the stars to the Southern Cross, are not necessarily close together in the sky in reality.

In fact, the stars of the Southern Cross are a very good example. The stars are dispersed three dimensionally in the sky. They are at different distances. From our position they make up the Southern Cross. Anywhere else in the Universe, or any where else in our own galaxy, they would not appear like the Southern Cross. They would take up a completely different shape. It’s just from our viewpoint they take up this interesting shape.

So going on, we have looked at Acrux, Beta Crucis or Mimosa. At the top of the Cross this is a star called Gamma Crucis. That is a relatively cool star so it’s an orange colour. Unfortunately, our eyes are not sensitive to colour in the dark, so we don’t normally pick up the colour with our unaided eyes. But with photographs, if you take a colour photograph, or look at colour photographs of the Southern Cross, then it’s quite obvious that Gamma Crucis has an orange colour. Its distance, it’s a relatively close star, is 88 light years. That is the closest star out of the five main stars of the Southern Cross.

Then going further clockwise, the star on the right is Delta Crucis. That’s a hot star, 364 light years distance. Then we come below Delta, and between Delta and Acrux we find the faintest star of the Southern Cross, Epsilon. If you look at the Southern Cross from a city you might not be able to see Epsilon, as I’ve said, but with a pair of binoculars it would be easy to find. That’s, again, an orange-coloured star like Gamma Crucis. It has a distance of about 230 light years.

Surrounding the Southern Cross we find a constellation of Centaurus, the Centaur. That constellation surrounds the Southern Cross on three sides. It’s to the east, which is to the left, above to the north and to the right to the west. So it is surrounded on three sides. Centaurus, or the Centaur, represents a Greek legend of half-horse, half-human creatures called Centaurs. These were very war-like and quarrelsome creatures.

Interestingly this particular Centaur that is there in the sky next to the Southern Cross is not a war-like creature. It represents a Centaur known as Chiron. That Centaur, Chiron, was known for his wisdom and his kindness. He was a teacher and he taught the Greek heroes of antiquity, Jason and Hercules. He taught them subjects like music, poetry and mathematics. As a reward he was placed by the king of the Greek gods, gods of the Greek mythology, Zeus, among the stars. Originally the Southern Cross, in Greek times, was just part of the Centaur and represented the hind legs of the Centaur.

The two main stars of Centaurus are the two Pointer stars, the Pointer stars which always point to the Southern Cross and the ones which enable us to find and distinguish the Southern Cross from other nearby stars which look like the Southern Cross. You can always recognise the Southern Cross by the two Pointer stars. Out of the two Pointer stars, the one further away from the Cross in the sky is Alpha Centauri, also known by its Arabic name of Rigel Kentaurus which means the Centaur’s Foot.

If you look at Alpha Centauri through a telescope, you can see it is a double star, two stars really close together in the sky. In fact, they are one of the nicest objects to look at through a small telescope. To me, the two stars appear like a pair of distant car headlights. These two stars circle around each other in about 80 years. So they take 80 years to go around each other. They were the furthest apart in 1995, and since then they’ve been coming closer together.

The brighter of the two stars is very similar to our own Sun, while the fainter star is a somewhat orange star. It’s a little bit less massive than our own Sun, a little bit cooler, but it is a slightly larger star than our own Sun.

There is a third star in the system, which is known as Proxima Centauri. Now, we cannot see that through a small telescope, because it is quite a long way away. It’s two degrees away, so it’s four times wider than a full Moon. That’s normally outside the field of view for a telescope. That’s one reason why we can’t pick it up. The other is that it’s a very faint star; it’s a little dwarf star. It gives off only about one-ten-thousandth as much light as our own Sun

The three stars of Alpha Centauri, the Alpha Centauri system, are at a distance of about four and a third light years from Earth. That is, light left Alpha Centauri four and a third years ago, so not that long ago four and a third years before reaching us.

This makes Alpha Centauri the three stars of Alpha Centauri, or the Alpha Centauri system the closest star system to Earth. But in fact, Proxima and you can guess that by the name Proxima is just a little bit closer than the other two. So, Proxima is in fact the closest star to Earth, apart from our own Sun. Proxima was only discovered relatively recently. It was discovered in 1915 by an astronomer called RT Innes. He was an ex Sydney astronomer, who moved to South Africa, and made the discovery while working there.

The other star of the two Pointers is Beta Centauri. That’s the one that appears closer to the cross in the sky, and that is much further away. That is 525 light years away, so once again demonstrating that two stars that appear close together in the sky, in fact can be very large distances apart in reality. So, Beta Centauri is 525 light years away from us.

It’s a very hot, massive star, giving off something like 10,000 times as much light as our own Sun. Through a telescope you can just see that it’s a double star. You can see a fainter star associated with the main primary star though this fainter star is still 400 times as bright as our own Sun.

Finally, before we wrap up this view of the stars in July, I’ll mention another object in part of the constellation of Centaurus, an object called Omega Centauri that is known affectionately to astronomers as Omega Cen. This is a globular cluster, a huge ball of several million stars. It’s believed to contain five to 10 million stars. This ball of stars circles independently around the centre of our own galaxy. It’s the most massive of the 160 or so globular clusters, similar balls of stars, that we know about in our galaxy, the Milky Way.

At 16,000 light years away it’s relatively close for a globular clusters. It’s only visible from the Southern Hemisphere, and it is a very nice object to study. It circles around the centre of our galaxy in the opposite way to the way to the stars, which suggests that it has a rather interesting history.

It has been suggested that it is a remnant of a small galaxy that was swallowed a few billion years ago by our own galaxy, the Milky Way. This is the remnant the very central part, the nucleus of the small galaxy, and we see it as the globular cluster Omega Centauri, Omega Cen. It is visible to a naked eye from a dark sky, but in a city it can easily be picked up with a pair of binoculars.

Back in 1985, when Halley’s Comet was nearing the Earth before its close approach in 1986, it passed right by Omega Cen. It looked exactly like Omega Cen, and a lot of people, at that time, who saw it in their binoculars thought incorrectly that Halley’s Comet had split into two.

Let us now look at the planets and other events in July 2009. This year, on 4 July, the Earth will be at its furthest from the Sun. That is an event we refer to as aphelion. That happens somewhere around noon on 4 July.

Now, this seems to make sense that the Earth is furthest from the Sun in the middle of the Australian winter. But in fact, it has little effect on the temperature. If you think about it, you realise that on 4 July when the Earth is furthest from the Sun, it is the middle of summer in the Northern Hemisphere. So, the temperature is not really affected by the varying distance of the Earth from the Sun.

It does have an effect on the lengths of summer and winter. The fact that our winter takes place with the Earth furthest from the Sun it is the time that the Earth is moving the slowest around the Sun – that means that our winter is a little bit longer than it would be otherwise, because we are furthest from the Sun.

Similarly, our summers in January when the Earth is closest to the Sun then the Earth is moving faster around the Sun. So, our summers might be a little bit warmer, because we’re closer to the Sun at that time of the year. But, our summers are quite noticeably shorter than they would be otherwise.

The main planet that is visible in the evenings is the planet Saturn, and it’s high up in the north-west. On 25 July, the crescent Moon will appear very close to Saturn. The crescent Moon will be to the left, or west, of the planet. The planet Mercury starts becoming visible in July, and it will appear very low in the west, just near the end of the month. So, it will join Saturn in the western sky, but much lower in the sky, very late in the month.

There are more planets visible in the morning, so those of you who rise early in the mornings can see the planet Venus and the planet Mars as well as the planet Jupiter before sunrise. Venus is in the north-east, as is Mars, while Jupiter is in the western sky.

That completes our discussion of the planets and other events in July 2009. You can catch this podcast on the Sydney Observatory blog, www.sydneyobservatory.com/blog. My name is Nick Lomb. I’m curator of astronomy at Sydney Observatory.

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This month’s audio sky guide is presented by Dr Nick Lomb, Curator of Astronomy at Sydney Observatory. You can listen online, or download the audio onto your ipod or mp3 player. Links to the audio and the star map are below.

There is more information and detail in our annual book, written by Dr Nick Lomb, ‘The Australian sky guide’ – however, this year’s has been so popular, it has sold out. If you are interested in the ‘2010 Australian sky guide’ with information and star maps for months from December 2009 until December 2010 inclusive, plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information, you can purchase it online or at Sydney Observatory and Powerhouse Museum shops from November.

The free monthly night sky map PDF (below) shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.

July 2009 night sky map

Read the transcript.

Proto-sunspot AR 11017, drawn by Harry Roberts

“The Sun is behaving in an unexpected and interesting way” said NASA’s Dean Pesnell in announcing yet another prediction for solar cycle 24 on 2009 May 29, adding “It turns out that none of our models were totally correct”. Whatever the prediction for the new cycle, sun-watching has never been this exciting; let me suggest why.

In old cycle 23 (C23) the sun “chose” to put much of its energy into solar flares – producing the strongest flares for thirty years, maybe for 100 years. Then, perhaps not surprisingly, it plunged into the deepest minimum for 100 years (i.e. since 1911).

And now, well into this deep minimum, we see some unusual activity on our star, activity perhaps last seen in 1911. In particular we have begun to see large faculae regions (FR) appear that are almost spotless. During normal solar activity large faculae regions evolve closely with major sunspot groups – with all authors noting one exception, the tiny spotless faculae at the sun’s poles during solar minima (the polar faculae).

NASA dubs the current large faculae regions “proto-sunspots” and speaks of them as “spots trying to emerge”. None of my texts (ranging from Bray to Zirin ) remark “proto-sunspots struggling to emerge” – and while much is known of faculae generally, these FR are perhaps “new” to solar science. Maybe they were common during that last deep minimum in 1911 – and have been forgotten in the modern literature?

They would be hard to interpret were it not for Livingston and Penn’s “Sunspots May Vanish” paper, first deemed “controversial” but now looking plausible. Is it possible that the FR are in fact normal C24 sunspots but their umbrae are too warm to be visible against the bright photosphere –as predicted by the above authors to occur in 2014 – but well ahead of schedule?

Many attributes of a normal sunspot region (AR) are present in these regions e.g. conspicuous bright faculae, with plage and filaments in H-alpha Flares erupt in them, but without strong spot fields the flares do not exceed GOES B-class, and the faculae seem to spread across wide areas. Yet only a few tiny spots or none at all emerge in the faculae regions (Fig1).

Several C24 “proto-sunspot” regions have occurred, I’ve counted six , the biggest and most recent being AR 11017. First seen May 11 as a very large patch of bright faculae 25º behind FR +22/218 (second rotation AR 11015), the new spotless FR was centred at +19/192 but covered 13º in both latitude and longitude – a faculae region about 5000 area units in size! Next day a single small spot arose at +18/194, with filaments and plage, and on the 13th a remarkable sight occurred. A grey smudge was in good seeing shown to be sixteen tiny spots in two tiny clusters about 5º apart, embedded in bright plage and tangled filaments. The clusters were seen next day, now 6º apart with 8 to 10 tiny spots – but hard to see.

The magnetic polarity of proto-sunspot AR 11017, drawn by Harry Roberts

Mt Wilson digital magnetogram for May 13 shows the extent of the faculae (with fields of ~10G) and with concentrated stronger field coincident with the two spot clusters of about 150G. In fact the magnetogram gave the strong impression that the group was a large bipolar sunspot pair with umbrae about 6º apart (Fig2). Mt Wilson’s Babcock magnetograph showed umbral fields in the two clusters of 1700G – just 200G above invisibility at 1500G.

I suspect this record (of 13th) resolved individual magnetic flux “ropes” each about 1000km diameter separating at the sun’s surface (photosphere) –only some having fields strong enough to appear dark. More normall umbral fields (~2700G say) would have caused large dark p and f umbrae to form instead the tiny spots. This was a memorable observation, and I suspect we are watching sunspot slowly umbrae fading from view as the “Spots May Vanish” authors suggest –events that are unfolding ahead of schedule, for unknown reasons.

By email I suggested to Livingston that these regions (FR) are like Alice’s Cheshire Cat, with only the “smile” (the faculae) remaining once the “cat” (sunspot umbrae) has faded. He liked the analogy and advised he had a week coming on the McMath-Pierce solar telescope shortly. May he have some sunspots to measure.

Magnetic field strength for solar cycle 24 sunspots, drawn by Harry Roberts

Mt Wilson has reported umbral fields for 14 of the 17 C24 groups that have so far emerged. Plotting these fields (Fig 3) shows very weak levels in the first 4 groups (2008), rising to a modest peak of ~2300G in AR11008 2008 November. From there (2009) fields have declined with each new C24 spot group – in line with the Livingston-Penn prediction – and of the six C24 faculae regions seen so far three have been spotless. Currently umbral fields lie just above invisibility (at ~1500G). Note the authors’ published graphs show a steep zig-zag in measured field – with a steady decline only when averaged, so perhaps we are in a short-lived “trough” and values may partly recover to fall again. – but current events seem to confirm, amazingly, that sunspots ARE in fact vanishing.

Harry Roberts (Sun and Moon observer and member of the Sydney City Skywatchers)

Students interested in work experience at Sydney Observatory can contact us via email on observatory@phm.gov.au

Students interested in work experience at Sydney Observatory can contact us via email on observatory@phm.gov.au

Sunset from Sydney Observatory on 22 June 2009, one day after winter solstice. At this time of the year the Sun moves slowly as indicated by the name solstice which means, “the day the Sun stands still”, so there would be little difference compared to the day before. As indicated on the image, at the winter solstice the Sun sets at its furthest north for the year. Image Nick Lomb

At sunrise on the winter solstice in 2009 I was back at Elizabeth Bay House as in the previous year. Once again the rising Sun shone along the long hallway that cuts through this beautiful historic house dating from the 1830s. This time though the effect was a little late as the Sun had to clear a large bank of cloud on the horizon.

Watching the midwinter sunrise at Elizabeth Bay house in 2009. Notice the shadows from people’s legs being parallel to the hallway. Image Nick Lomb

The big question about Elizabeth Bay House is whether its original owner Alexander Macleay had the house especially oriented towards midwinter sunrise when it was built from 1835 onwards. As indicated on the Google image below the natural orientaion of the house is towards the Harbour, that is, in this case Elizabeth Bay. Did he tweak the direction slightly just for the sunrise or was it accidental? Without any writings from Macleay it is pure conjecture. My initial guess on looking at the image below is that it was accidental.

A Google map image of Elizabeth Bay with the direction of midwinter sunrise indicated

Alexander Macleay would probably have been familiar with the orientation of Stonehenge, the megalithic monument in England, towards the midsummer sunrise and, in the opposite direction, to the midwinter sunset. This monument was often mistakenly attributed to the Druids. And this is where an email from Dr Daniel Nicholls comes in:

Stair entrance to the grotto near Elizabeth Bay House, image Daniel Nicholls

I read with interest the article from Saturday’s SMH. I wondered whether you were aware of the stone grotto and altar, bearing the inscription 1835, situated in the old Elizabeth Bay House grounds, some metres to the East, now beneath the foundations of a building. The grotto has the distinctive oak leaf pattern of the Druids and perhaps some grape patterns. Sea shells are implanted in the cement. This grotto may provide further evidence that Alexander Macleay indeed built EBH with the winter solstice in mind. The altar would have been exposed to the rising sun prior to the encroachment of buildings obscuring the bay.

Oak leaf patterns in grotto, image Daniel Nicholls

So maybe Alexander Macleay had Stonehenge and its supposed Druids in mind when he commissioned the house. It would be good to know.

The Hickson 44 Group of galaxies. Image courtesy Space Telescope Science Institute

Welcome to the next long-awaited instalment of the Continuing Adventures of Gerald – Mudgee Star Party.

Well after the seemingly continuously cloudy weather of the last few months and Gerald [according to rumour Gerald is a garden gnome - Nick] & I were chomping at the bit to catch lots of faint photons. The weather report prior to heading up was not exactly encouraging with showers forecast for the Friday rain on Saturday and showers Sunday. At least Thursday seemed okay …

So off we set on Thursday morning with, as usual, with all the lingering nagging doubts about ‘what vital thing have I left behind’ that only go away when you finally unpack it all. This year I did forget something – but it wasn’t vital – I forgot to take a fork. The knife, spoon, tea-spoon etc all made it in but the fork somehow missed the boat. Not exactly the end of the world. Most importantly all the bits of the ‘scope made it.

On the way up the year before last I stopped in briefly at Hartley for a nose-around the old court-house and other buildings that I remembered so fondly from a 5th-grade excursion in 1973. This time with a camera to record it for posterity. It also allowed Gary and Taylor to catch-up the 20mins they were behind and we met at Lithgow for lunch at the truck-stop. The countryside there looked well-watered and pretty green but does brown-off a bit as you head north and west to Mudgee. Suitably refreshed the final leg to Mudgee took no time at all. By mid-afternoon we were unpacking and setting up under a half-half sky down in the bus-park (valley of the dobs) beside our new digs – an old 15ft Millard caravan that John had procured for less than a song and had put a lot of work into to make not only habitable but very comfortable.

It was around this time that Gary discovered that he’d left something fairly important behind – his sleeping bag. With some cold nights forecast – not pleasant.

As it turned out, as the afternoon waned and darkness set it the sky improved nicely and gave us an almost full-night’s observing. The SQM [Sky Quality Meter]gave a reading of 21.55 + a ZLM of 6.39 improving over the course of the night to 21.71 = a ZLM of 6.5. The seeing was a bit better than average and I’d have rated it 7/10.

The soundtrack for the night (albums) was: Drama – Yes, The Wall – Pink Floyd, Amarok – Mike Oldfield, Led Zeppelin III – Led Zeppelin, Let it be – The Beatles, Islands – Mike Oldfield, Animals – Pink Floyd, The Planets – Holst, The Firebird Suite – Stravinsky.

After a few test objects to make sure everything was tickety-boo and a good look at Saturn which was really lovely at both x247 and x317, I settled into my looooong list of unobserved galaxies in Leo and then later on Virgo.

[Among Les's looooong list were the Hicksons]

The Hickson 44 Group (shown above) is one of the nicest compact groups of eg’s [galaxies] in the sky:

-97 is the smallest and faintest of the group but is clearly elong in PA 120 and pointed at by -90, it is only about 2.5′ away. Fairly faint, like a ghost image of -90, small elong spindle, about 1.5′ x 10″ of consistent SB.

-90 is a fairly large bright eg with a beautiful *ar nucleus. Classical almost edge on spiral eg in about PA 120 brightens from blunt tips broadly and slightly to the axis nr centre and at centre is a strong stellar nucleus surrounded bu a strong, slightly elong core zone. The S side of that core zone seems underlined as though there is a dark lane there.

-88 is to the NE by 4′ from -90 and is just S of a 9th mag *. Fairly HSB round 1.25′ diameter, round elliptical looking eg with a mod even brightening profile with a small zone nr centre no nucleus visible.

-85 is to the SW by 12′ is lower in SB than -90, fairly bright, 1.75′ x 1.25′ in PA 150, growing broadly and slightly to centre where there is a small core containing a *ar nucleus.

Les Dalrymple, deep sky observer and guide at Sydney Observatory

Hyginus crater and its associated rille or channel plus a chain of craters, drawn by Harry Roberts

Cloud, cloud – more cloud! Anyone noticed how cloudy it’s been lately? Setting up in a clear patch I saw that trees would hide the Moon in 30 minutes! Seeing and phase were both nice, but what to sketch in the time available?

Rima Hyginus came into view – and I’ve sketched it a few times before – but now the chains of craters in the rift stood out more strongly than previously, so I reached for the sketch book.

Lighting at the site showed that the deep rima (rift or graben) stretching both northwest and east of Hyginus seemed to be more like a catena – i.e. a chain of small craters, with many craters positioned right on the rift. As well, the NW branch of the Rima seemed to have two distinct breaks in it (arrow b). Here a faint stretch of trench ran between bright circular craters. Perhaps the sun’s altitude over the site (24º from ‘Virtual Moon’) “washed out” the shallower stretches of rima – making them invisible at the time.

The “craters” however still had distinct shadows, and it was clear they were much deeper than the connecting rift. In places Rima Hyginus looked like a string of white sausages –elsewhere more like a string of brilliant pearls. This was most obvious on the NW branch, particularly at the farther end where several distinct round craters were seen. The larger “pearls” would be about 4km diameter, and being rimless, they cannot be impact features. Presumably material has collapsed into subsurface fractures to form these bright conical “craters”.

Inside crater Hyginus a bright notch in the rim shadow on the east side showed where light shone through the rift onto the crater floor The attached ellipse-shaped “crater” (arrow a) is perhaps a branch of the rift that failed to develop. Like the rest of the Hyginus formation there is no sign of impact origin – and all the “craters” are rim-less. Hyginus itself is 11 km diameter and 800m deep.

Schultz’s “Moon Morphology” p364 tells us “Hyginus is centred in a diffusely bordered low-albedo region (seen) more easily under full solar illumination”. This looked like several fans of dark ash spreading away from the main crater and somel smaller craters to the left in the figure (dotted arrows). I wondered why, if these fans were volcanic, they are seen only on the south side of the Rima. Crater counts seem the same on both north and south sides of the formation – so on an airless Moon you would expect ash to spread evenly in all directions. Such ash is found spread around rimless craters, or pits, in Alphonsus, and the dark deposits may not be of high temperature origin.

A few nearby craters were recorded, Hyginus B is 30km to the left, and a bright halo crater lies to the south.

Enjoy Moon watching if you can find some gaps in the cloud.

Harry Roberts (Sun & Moon observer and member of the Sydney City Skywatchers)

Diagram of the Sun on the morning of Monday 8 June 2009 (Australian time) drawn by Monty Leventhal OAM. Though there are no sunspots, 10 prominences are shown scattered around the edge or limb of the Sun

Previous readers of this blog would be aware of the work of amateur astronomer and member of the Sydney City Skywatchers, Monty Leventhal, as his full disc drawings and digital images of the Sun are regularly used on this blog. Examples are shown in this post. Monty has received awards previously from international astronomical organisations, but now his work has been recognised by the wider community.

“Digital filtergram shows a nice Prominence on the SW limb reaching an approximate height of 56,000 km”, taken on 16 May 2009 at 22:25 UT, image by Monty Leventhal OAM

I was most gratified to see in this morning’s paper that Monty was included in the Queen’s Birthday honours list. He received a Medal (OAM) in the General Division of the Order of Australia. The citation reads “For service to science through volunteer roles at the Sydney Observatory.” Congratulations Monty!

As indicated by the citation he not only observes the Sun on a regular basis, but he has also been volunteering his time to share his passion for the Sun with visitors to Sydney Observatory. You can meet him at the Observatory and look his telescope on every second Sunday.

“Digital filtergram shows a very active Prominence on the NE limb”, taken on 22 April 2009 at 23:15 UT, image by Monty Leventhal OAM

The OAM to Monty is gratifying not only because it recognises his long standing dedication, but it is also a recognisition for the work of amateur astronomers. As the first amateur to be recognised (I am happy to be corrected on this), I hope that Monty will be the trail-blazer and there will be recognisition for many other deserving amateurs in the future.

Well done Monty!

Drawing of a sunspot on 14 April 1869 by James Cook

While working on a new catalogue for the library of the Sydney City Skywatchers, an intern found an intriguing album of ink and pencil astronomical drawings. They are mainly of Mars at its 1879 opposition and Jupiter from 1869 to 1879. Plus there is the sunspot drawing above. That drawing indicates a complex sunspot group such as probably would have been seen often during that year of solar maximum.

The sunspot drawing and some of the others are signed by James Cook. I have not previously heard of an amateur astronomer by that name and certainly he would not be Captain James Cook who had been killed in Hawaii in 1779. The mysterious Mr Cook appears to have used a number of telescopes as some of the Jupiter drawings indicate a “10″ Metallic Newtonian” while others say “Aperture 15 inch”.

Active Region 1019 on the Sun visible on 2 June 2009, drawn by Deirdre Kelleghan

Amateur astronomers are still drawing and imaging the Sun in 2009 although the Sun is currently in a state of exceptionally low activity. Above is a recent drawing by Irish astronomical sketcher Deirdre Kelleghan who twitters. She says of the drawing:

We are having an unusual few days of hot hot sunny sun , so a bit of solar observing was just the ticket for relaxing in my garden.

Active Region 1019 June 2nd 2009
PST 40 mm / 8mm TVP Up scaled by eye
Pastel, and Conte on black paper
11:00 UT

A prominence on the Sun imaged on 29 May 2009 (Australian date) by Monty Leventhal

Monty Leventhal of the Sydney City Skywatchers is another diligent solar observer. He says of the above digital image:

Today’s Digital filtergram shows a Prominence reaching an approximate height of 84,000 km.

Date:- 28-5-09
Time:- 22.25 UT
Conditions:- Good but very cloudy
Supported by the Donovan Astronomical Trust, Sydney. Australia.
Camera:- Canon 300D
Filter:- DayStar T-Scanner. 6Å.
Telescope:- Meade S.C. 10 inch

Over the next few weeks we will look at more of James Cook’s rediscovered drawings.