Archive for the ‘Astronomy blog’ Category


A short-lived outburst from Comet 67P/Churyumov–Gerasimenko on 29 July 2015. The jet lasted barely 30 minutes. Image © ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

As Comet 67P/Churyumov-Gerasimenko reaches its closest point to the Sun, perihelion, on August 13, its activity is increasing. This short lived jet was spotted by the narrow angle camera on board ESA’s Rosetta spacecraft. Heating from the Sun, and the rotation of previously dark areas into sunlight result in an increased release of dust and gas as the comet approaches the Sun. From Earth comets are often most easily seen after their “perihelion passage”.

The gas released is mostly carbon-dioxide. But many other organic molecules are also released. What would it smell like? The smell has been described as a combination of: rotten-egg smell, horse-stable odor, almond and vinegar!

If you want to experience the smell for yourself book in for Warwick Holmes full-sensory presentation, “Philae and the Rosetta Comet Encounter” during Sydney Science Festival at the Powerhouse Museum, Thursday August 20.

August 2015 night sky guide and sky chart

Published by Melissa Hulbert on August 1, 2015 No Comments

To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory Astronomy Programs Coordinator.
Mel suggests stars and constellations to look out for this month include Scorpius, with the red star at its heart, Antares; Sagittarius (which looks more like a teapot than a centaur); Crux – more commonly known as the Southern Cross; and Ophiuchus, the 13th sign of the zodiac! Mel also tells us the best times and dates to try to see the planets Venus, Saturn, Jupiter, Mars and Mercury.

We provide an embedded sky map (below) and an August 2015 night sky chart (PDF) which 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.

Star Map Aug 2015

Our annual book, ‘The 2015 Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2014 until December 2015 inclusive (next year’s, likely to be available from November, will have months from December 2015 to December 2016), plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information. You can purchase it ($16.95) at Sydney Observatory and Powerhouse Museum shops or other good bookshops, or online through Powerhouse Publishing (additional packing/postage costs apply).

READ THE SKY GUIDE (after the jump)



Warwick Holmes holds aloft a 3D printed model of comet 67P/Churyumov–Gerasimenko. The real comet is even darker than this model. Photo Andrew Jacob © MAAS, Sydney.

Warwick Holmes worked for over four years at the European Space Agency (ESA) on the Rosetta/Philae mission to comet 67P/Churyumov–Gerasimenko. He recently visited Sydney Observatory and brought along his model of the comet. It is difficult to photograph because it is jet black. The real thing is blacker still!

Warwick will present an insider’s view of the mission, including the spacecraft design and the images and the science acquired, during Sydney Science Festival, Thursday August 20, 6:30-8:00pm. Booking required. 

Aroma Festival Comes to Sydney Observatory

Published by Melissa Hulbert on July 24, 2015 No Comments

Aroma Festival

Coffee/tea and astronomers have long had a symbiotic relationship – there is nothing like a good cuppa at 2am with still a few more hours of observing to go!

With that in mind, this Sunday (26th July) is The Rocks Aroma Festival of which Sydney Observatory is a part.

From 10am-4pm our barista, Jan, will be brewing the finest blend on a unique coffee bike/cart.

With every day tour ticket purchase enjoy a Cosmic Coffee, Aromatic Black Hole Tea or a Solar Hot Chocolate and a star-inspired chocolate treat.

With sunshine forecast, what better way can you spend a relaxing Sunday then by enjoying a tour, a brew and views from Sydney Observatory?

See Venus, Jupiter and the crescent Moon this weekend

Published by Andrew Jacob on July 17, 2015 No Comments

The Moon, Venus and Jupiter are close in the western sky after sunset this weekend – Saturday & Sunday 18 & 19 July 2015. Map generated using Stellarium.

This weekend, 18 & 19 July 2015, the crescent Moon, Venus and Jupiter make a nice grouping in the western sky in the evening twilight.

The Moon may be first visible on Friday night as a thin crescent  below both Venus and Jupiter. Venus is very bright and is seen above the fainter Jupiter. On Saturday the Moon has moved much closer to Jupiter – as shown in the above graphic – and by Sunday the Moon will be just above Venus.

The appearance of the crescent Moon on Friday evening is also a marker for the end of Ramadan for many people.


Venus is visible to the naked eye at present. On Sunday 19 July 2015 the crescent Moon will help you locate it. Map generated using Stellarium. Warning: Do not look at the Sun directly.*

This weekend is also a good time to view Venus during  daylight hours. This is only possible when Venus is at its brightest. On Sunday shade your eyes from the Sun and locate the crescent Moon in the sky. Nearby you will see a bright “star” – this is Venus. The graphic above shows the position of the Sun, crescent Moon and Venus at midday (AEST) on Sunday July 19, 2015, looking north.

Ross Mitchell, a Skywatchers member, and regular contributor to these blog pages located Venus by eye recently and photographed it – as you can see below Venus also displays a crescent shape. Ross has sent a few images and I will post more soon.

*Warning: Please note that photographing Venus when it is so close to the Sun during daytime requires great care and should only be attempted if you understand how to do so safely. Viewing the Sun with binoculars, telescopes and other optical equipment can lead to permanent, irreversible eye damage.


The crescent Venus photographed by Ross Mitchell, “Thursday 9th July 2015 at 12:12 AEST through a 30x theodolite using eyepiece projection, image cropped and straightened.”

Keeping up with the New Horizons Pluto flyby

Published by Andrew Jacob on July 14, 2015 No Comments

And finally it’s July 14 2015. The New Horizons Pluto fly-by happens today!


After we receive its last approach image at about 5:30pm* AEST New Horizons turns towards Pluto and will be out of touch for many hours. Closest approach occurs at 9:50pm AEST but the spacecraft is busy observing Pluto and its moons then. It wont be until about 11am* on Wednesday July 15 that we receive the first data from the close encounter.

There are numerous places on the web to keep in touch with what is going on. Here are just some of them…

Watch the National Geographic Channel live stream.


See the NASA New Horizons homepage …

for a map showing New Horizons present location,

and a detailed Event Timeline of all the spacecraft imaging and science activities (Note the times are in US east coast times, add 14-hrs to get EAST)

and the Latest News and Images

Watch the NASA TV stream. The flyby stream begins at 9:30pm AEST and the first data from the closest encounter should arrive around 11am on Jul 15 AEST)


You could also follow the New Scientist Live Blog (begins at 8:45pm AEST) or the Slooh online show (but it seems you need to login and pay a subscription for Slooh now).


For Australia’s contribution check out when the Canberra/Tidbinbilla DSN dishes are communicating with New Horizons.

And lastly the Google Doodle shows New Horizons passing Pluto complete with the ‘heart’ feature.

*I have to admit I am having trouble deciphering all the timings! While I’m sure closest approach happens when it is 9:50pm AEST the other timings are complicated by conversions between EDT (USA east coast daylight saving time), UT (essentially GMT), AEST (Eastern Australia Standard Time) and the almost 4.5 hours it takes the signal to reach Earth. Not all my sources are clear about which time they are quoting.


AR12371: Delta Groups and Flares of Solar Cycle 24. Sketch and copyright Harry Roberts ©, all rights reserved.

Regular solar observer & correspondent Harry Roberts reports on his observations of flares seen on June 20-21 (UT). These flares caused aurora that were visible from Sydney, and similar latitudes, on June 23, 2015.

AR12371: Delta Groups and Flares of Solar Cycle 24.

G. E. Hale’s magnetic classification of sunspot groups did not at first include class Delta – this category was defined by H. Kunzel in 1960 as ‘two or more umbrae of opposite magnetic polarity in a single penumbra’ (pu).

Since the start of Solar Cycle 24 (SC24) there have been (writer’s count to end April 2015) 39 Delta groups, the first being AR11045 in 2010 Feb. Between them they have hosted 29 GOES X-class flares (i.e. flares with an X-ray flux >1×10-4Wm-2). The strongest was an X6.9 in 2011 July.

In SC24 thus far, not all Delta groups produced GOES X-class flares, but all such flares were the product of Delta groups: i.e. to see an X-class flare we must monitor Delta groups closely. AR12192 of 2014 October, a Delta group, produced six X-class flares: the strongest an X3.1; also that group was the largest sunspot for over twenty years.

  1. This would have appeared on the Sun about 2015 June 15 – but went unseen until the 19th (UT) due to heavy cloud. By then it had been dubbed class Delta by NOAA and contained about 24 spots: its irregular shaped preceding (p) spot and jumbled large following (f) spots were typical of the class. No polarity data was posted by Mt Wilson that day but data for the 20th showed umbrae of unlike ‘sign’ in the large irregular (f) spot, along with linear umbra and multiple light bridges in the elongated (p) spot (Fig. Preflare): a classic Delta.

This was one of the few recent spots that promised imminent flaring; when the white light (WL) log was done, H-alpha patrol began at 21ST 00:45 – and, amazingly, the expected flare in fact arose at 01:30 reaching visual class 1N!  Three logs show the progress of this unusual flare which had two separate peaks of M-class. AR12371 however did not host any X-class events.

Preflare: The Fig shows the group as logged in WL – with Mt Wilson polarity from earlier added, showing large umbrae of preceding (i.e. p) ‘sign’ (violet) amid the following (f) spots: the Delta configuration. The polarity boundary or ‘inversion line’ is dotted blue based on SDO HMI magnetogram – it matches Mt Wilson data – but with a hint of a smaller one below the big (p) spot. Note the flares will develop along this configuration.

Obscured umbrae. Some authors note that precursors to ‘big flare’ events include the ‘obscuration of spot umbrae by H-alpha emissions’. Often logged in the past, the writer noted that the intricate light bridges (LB) in the big (p) spot umbra (seen in WL), were obscured in H-alpha by emissions of plage brightness (Fig) – and unchanged during the ensuing flares.

Flare 1(Fig 1). This began to brighten at 01:20 and by 01:30 reached GOES M1 level – slender ribbons stretched from the (f) spot at +14,297 to a fiducial point at ~+8,304, south of the big (p) spot. By 01:42 M2 level was reached (Fig 2): now the lesser ribbons were gone, yet those of the (f) spot remained bright – in fact grew brighter. Note the changes to filaments at points X and Y.

Flare 2. By 01:55 the flare had faded to 1F(visual) and the session ended at 02:05. The ‘scopes were stowed and calculation of coordinates began. A glance at the GOES Flux about 02:40 showed another strong flare in progress: perhaps in AR12367 – the only other group on the disc? In haste, the scope was reassembled to reveal a second flare in AR12371! It was 02:47 before the ‘new’ flare could be logged – when clearly past its peak (Fig 3).

Twin Peaks. The earlier M2 had peaked at 01:40 and the M2.7 Flare2 peaked at 02:34 – almost an hour apart –unusual in the writer’s experience. Flares mostly discharge their energy source (entangled strong field and helicity, perhaps) in one event – and some time is needed, usually hours, before a repeat flare.

Flare2 was unusual in retaining much of the geometry of earlier event – in fact the first flare never fell below M1 before the rise to M2.7. The second flare involved new ribbons extending from the remnants of Flare1 across to the big (p) spot along paths similar to the earlier event.

Flare2 was rated visual 2F at 02:47 and when the session ended at 02:52 was still at GOES M1.7 level. Both events remained at peak brightness for extended periods – Event2 for ~30mins: most unusual for current flares – and reminiscent of ‘great’ flares of previous solar cycles.

Fig 4 (below) shows the group the next day: changes include the re-shaping of the (p) spot – to become rounder; and the (f) cluster has split along a line ~ the inversion line, though violet field is still mixed with red as shown.

The hectic session of 20/21 reminded me of the importance of Delta groups in the account of flaring in SC24: a cycle remarkable for the weakness of its X-class flares.


AR12371: Delta Groups and Flares of Solar Cycle 24 – the day after. Sketch and copyright Harry Roberts ©, all rights reserved.


Harry also provided the following plot showing the X-ray flux as measured by the GOES spacecraft.


GOES spacecraft X-ray flux of June 20-21 UTC. The M2 and M2.7 flares observed by Harry are highlighted. NOAA/SWPC.


Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.




Sun.2015May13.Low res

A hedgerow prominence on the Sun, May 13, 2015. Pastels and Conte on black paper. Deirdre Kelleghan, Co Wicklow Ireland. Photo and copyright Deirdre Kelleghan ©, all rights reserved

Deirdre Kelleghan is a regular contributor to this blog. Recently she sent us this lovely sketch of the Sun. Most astronomical objects have a more or less static appearance. Our Moon shows regular changes in shape and the planets moons’ change position. But the Sun presents an ever changing face – every day there is something new and interesting to see. With an H-alpha filter the view is particularly fascinating.

As Deirdre explains,

May 13th I went out to sketch Active Region 2339 in h-alpha but when I saw this massive Hedgerow type prominence on the limb it had to be done.

The sketch was made at 13:33UT on May 13, 2015 at Bray, County Wicklow, Ireland. Deirdre used a PST 40mm H-alpha telescope with an 8mm eyepiece giving a magnification of 50x. The sketch is pastels and Conte on black paper.

Hedgerow prominences, as their name implies, are groups of solar prominences lined up along the Sun’s limb that together resemble a hedge – some better kept than others!

Deirdre Kelleghan is an artist, astronomer and educator and a regular contributor to the Sydney Observatory blog.


Pluto – New Horizons images vs the 2010 “Buie” maps

Published by Andrew Jacob on July 7, 2015 1 Comment

In my previous post about Pluto I included three maps, not images, released in 2010 and laboriously made by a team led by Marc Buie of the Southwest Research Institute, Colorado. Fortuitously, the latest New Horizons image also shows three views of Pluto. How do the 2010 maps compare to the 2015 images?


These maps of Pluto’s surface were released in 2010. The north pole is tilted towards Earth here. NASA, ESA, and M. Buie (Southwest Research Institute).


These New Horizons images were released on July 7, 2015. The tilt of Pluto is similar that in the 2010 maps. However, the longitudes are different. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

The maps and images show Pluto with a similar tilt, north pole towards us, of about 30 degrees. However, the central longitudes are different making a direct comparison difficult. But the following graphic shows the full set of 2010 maps.


Maps of Pluto displayed at 30-degree intervals of central longitude. Compare these to the New Horizons images. NASA, ESA, and M. Buie (Southwest Research Institute).

And now we can compare them.

Let’s first look at the left-hand 2015 image, at 133-degrees. Comparing it to the 2010 map at 120-degrees we see clear matches between the dark feature along the equator (at the bottom of the disc), the bright “square” feature on the right and the dark region surrounding the “square”.

Now the middle 2015 image at 63-degrees. We compare this to the 60-degree 2010 map. The correspondence in features is less obvious. The 2015 image shows the dark equatorial region continues, but its form does not appear to closely resemble the 2010 map data. The 2015 image shows a subtle dark region across the middle of the disc. In the 2010 map data this region appears more pronounced and connects to the equatorial dark region. Maybe this region has frosted over in the intervening years? It was already clear in 2010 that some features of Pluto were changing with time. The clearest correlation is a dark region ‘chord’ on the upper-right of the 2015 image that also appears in the 2010 map data.

Finally, the right-hand 2015 image at 19-degrees. We can compare these to the 0 and 30-degree 2010 maps. Here the correspondence between features is least convincing. There may be a match between the intriguing equatorial dark spots in the 2015 images and the large dark circular region on the 2010 maps. The 2015 image shows a ‘donut’ and a bright spot in the lower half, and these may correspond to one or two bright spots in the 2015 maps.

In conclusion, the new images show features that do appear to correspond to features revealed five years ago in the 2010 maps. Yet, as we expected, Pluto’s surface is more complex and interesting than the old maps suggested.

It is worth noting that the data for the 2010 maps was collected by the Hubble Space telescope in Earth orbit – a distance of around 5.7 billion km with Pluto appearing about 0.1 arc-second in diameter. New Horizons was only 14-million km, and Pluto appeared about 1 arc-minute across (60x larger), when the 2015 images were taken. The remarkable correspondence between the two set of data gives us confidence in the image processing techniques used to make the 2010 maps. I am sure Buie’s team feels the years of effort & computer time they put in to make the 2010 maps was all worth it, and are well pleased with their results.

UPDATE, Jul 09 2015

Shorty after I posted the above images a new map of Pluto was released. I have combined the New Horizons image/map with two black & white HST maps from 1994 and 2002-3 so they are easy to compare. I have cut and rearanged the New Horizons map to match the odd longitude scale (beginning at 270 degrees) of the HST maps. Again there are similarities but also changes happening over timescale of a few years.


A comparison of a New Horizons Image/map with two older maps from HST. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute AND NASA, ESA, and M. Buie (Southwest Research Institute).


The most detailed maps yet of Pluto’s surface were revealed in 2010. NASA, ESA, and M. Buie (Southwest Research Institute).

In 1996 HST images showed surface features for the first time and revealed a complex, varied terrain. Then in 2010, after seven years of image processing, we saw Pluto in full colour for the first time. The colours are probably the result of a complex mix of materials, including carbon compounds, nitrogen ices and carbon monoxide frosts.

By this time we also knew Pluto had an atmosphere, seasons modified its surface features and it two more moons – we now know of five moons in total.


As New Horizons races towards Pluto the images are just beginning to surpass these old HST maps. It reminds me of the excitement and the surprise of discovery we felt in the 1980s. Back then the Voyager probes revealed the outer planets in all their glory – first Jupiter then Saturn, Uranus and Neptune. Only Pluto remained…




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