Archive for the ‘Astronomy blog’ Category

June 30, 2015 – A busy day in the solar system!

Published by Andrew Jacob on June 30, 2015 No Comments

What is it about June 30? Everything is happening at once!

The EOFY sales are on, our thoughts turn to tax returns and the coolest days of the year are approaching.

And in 2015 we also have…

Pluto momentarily hides (or occults) a faint star in the constellation Sagittarius. This happened at 0253am EAST.

It’s Asteroid Day, although there is some scepticism about the need for such a day.

Jupiter and Venus are almost at their closest in the western sky – get your binoculars out to see the crescent of Venus, mighty Jupiter and his moons all at once.

And to wrap up the day a leap second will be added – although this actually occurs at 10am on July 1st EAST.

Perhaps we need the extra time!

Pluto – where in the sky is it?

Published by Andrew Jacob on June 29, 2015 No Comments
Pluto20150629

Pluto is in the constellation of Sagittarius in the eastern sky during early evening. It is not visible to the naked eye. Chart generated by TheSky6 © Software Bisque, Inc. www.bisque.com

Pluto is getting a lot of attention at present (mid-2015). The New Horizons spacecraft is returning increasingly detailed images from the outer reaches of our solar system.

The chart above shows where to look for Pluto. It is not visible to the naked eye, and never will be from Earth. However, if you are lucky enough to have a telescope with an aperture larger than about 25-cm you should spot it – the electronic controls for your telescope, or this finder chart will help.

Without a telescope you can still locate its position. From most parts of Australia look east at around 7 to 8pm. Identify Sagittarius with the help of the chart above, it looks like a “teapot”. Follow the stars to Pluto.

 

Greg Nicholl captures Aurora Australis from Sydney

Published by Andrew Jacob on June 23, 2015 1 Comment
Greg Nicholl Aurora at La Perouse 23Jun2015

Aurora Australis #1 seen from Sydney early on June 23, 2015. Photographed by Greg Nicholl with a Canon 5D MkII. Photo and copyright Greg Nicholl ©, all rights reserved.

Greg Nicholl was fine tuning equipment on his telescope near La Perouse, in the south of Sydney, early this morning, June 23 2015, when he noticed a subtle pink glow on the southern horizon. Greg takes up the story…

This lead to me taking a few quick photos, predominantly in an effort to confirm what I thought I was seeing. My initial thoughts were that it could be an aurora, but knowing how rare it is to see one from as far north as Sydney I dismissed that idea fairly quickly, much to my regret now. Had I known, or at least trusted my gut feeling I would have taken more photos. Right place, right time… Just didn’t fully realise it!

Sightings of this aurora event were reported from elsewhere in Sydney and also from Tasmania and Victoria. As Greg says it is very rare to see an aurora as far north of the polar regions as Sydney (at a latitude of 34 degrees south) – to see beams and movement is a rare privilege indeed.

Greg Nicholl Aurora at La Perouse 23JUN2015

Aurora Australis #2, Sydney June 23, 2015. The Large Magellanic Cloud is also visible at upper middle. Photo and copyright Greg Nicholl ©, all rights reserved.

This aurora was caused by material from the Sun, released in a ‘full-halo’ coronal mass ejection (CME) on June 21, impacting the Earth’s magnetic field. The particles, mostly electrons, slam into our upper atmosphere causing it to glow in a ghostly red shimmering lightshow. Green colours were apparent in some images from further south. Aurora are completely safe to look at and they have no effect on the human body.

This geomagnetic storm was labelled “severe” and probably blacked out shortwave radio communication in the polar regions and may have affected the accuracy of GPS systems. Worse geomagnetic storms, like the Carrington event of 1859, are possible though extremely rare and could potentially have disastrous effects on our modern electronic lifestyle.

Greg’s photos were taken between 05:54 & 05:58 on the morning of Tuesday 23rd June 2015 using a Canon 5D Mk II with a 24 mm lens at f/2.8. Each photo was an 8 second exposure at ISO3200.

This storm has subsided slightly, but not fully. Keep your eyes on the southern horizon for the next couple of nights, particularly if you are in far southern Australia. You may see the Aurora Australis flare up again.

 

The Winter Solstice 2015 – long nights for winter viewing

Published by Andrew Jacob on June 19, 2015 3 Comments
VJM.WinterSolstice2015

Venus, Jupiter and the Moon are visible in the western sky after sunset this weekend. Here they are on Sunday evening, June 21, 2015. Chart created in Stellarium.

Has it been dark lately when you arrive home from work or school? Have you noticed the nights are long and the days are cold? Its winter solstice time again!

Solstice means “sun standstill”, but the Sun’s apparent motion doesn’t stop nor does the Earth stop turning. Since the beginning of the year (or the summer solstice to be precise) the position of sunrise (and sunset) has been shifting gradually northward along the horizon. On the solstice this northward movement ends – the Sun stands still on the horizon for a few days – and then it heads back south.

More precisely, in 2015 the southern winter solstice occurs at 02:38am AEST on Monday June 22. At this moment the Sun is at its most northerly point on its path through the sky and directly above the line of the Tropic of Cancer. While it will be dark in Australia, somewhere on the Tropic of Cancer it will be 12 noon locally and the Sun will be directly overhead. That somewhere will be in the west Atlantic ocean just north of the Dominican Republic and any yacht sailing there will cast no shadow.

Map.WintSolstice2015

The (southern) winter solstice in 2015 occurs with the Sun over the west Atlantic ocean north of the Dominican Republic. Map data ©2015 Google, Sanborn.

The solstice is a natural turning point in the year. Historically it was a time of new beginnings, of rebirth and revival. From now on the days will lengthen and the warmth of summer is on its way.

Although Monday is solstice day itself you wont notice much difference in the length of the day over the weekend. So make the most of the long nights and watch Venus, Jupiter and the Moon shining in the western evening sky.

Geoff Wyatt using the north dome telescope, image courtesy AAP Reuters

Geoff Wyatt using the north dome telescope, image courtesy AAP Reuters

To help you learn about the southern night sky, Sydney Observatory provides an audio guide/podcast, transcript of that audio, and a sky map or chart each month. This month’s guide is presented by Geoffrey Wyatt, Astronomy Educator at Sydney Observatory.

Geoff’s enthusiasm and humour are captivating but based on sound science, and enriched with stories of historical and cultural aspects of astronomy, including Indigenous and Greek myths. According to some Indigenous communities, there is an Emu in the sky (see picture, below).

The EmuGeoff reckons that June is a great month to see the brightest part of the Milky Way high overhead. So go on, get a blanket and a torch with red cellophane on the front, your free sky chart and audio (below) and go outside, and look up at the wonder of the Universe.

HEAR THE AUDIO
You can subscribe with iTunes or upload the (49 mins) audio to your iPod or mp3 player, or listen to it on your computer.

SEE THE SKY CHART
We provide an embedded sky map (below) and a June 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 June 2015

BUY THE BOOK
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, 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 TRANSCRIPT (after the jump)

(more…)

The calendar we use in civil society (the ‘Gregorian’ calendar) is a solar one – based on the time it takes for the Earth to orbit the Sun. Many religious calendars, however, are based on the phases of the Moon. These include the Catholic, Jewish and Islamic religious calendars. The dates of festivities, holidays and important events in the lunar calendar move by about 10 days every year within the Gregorian calendar.

The ninth month of the Islamic calendar, known as Ramadan, is the Islamic month of fasting. The Hilal, or crescent Moon, marks the beginning of the fasting period. However, there are differences of opinion on how to define ‘crescent’. While some simply demand an unaided sighting by eye of the crescent moon, others are leaning towards using astronomical calculations to avoid confusion.

The following astronomical data concern the new moons in June and July of 2015.

The simplest useful criterion is the lagtime between sunset and moonset. If that time is greater than 47 minutes (at the latitude of Sydney) the crescent Moon should be visible to the unaided eye after sunset and before the setting of the Moon.

The most common method of prediction is to use a scheme developed by Dr Bernard Yallop of HM Nautical Office and proposed in 1997. This scheme or algorithm involves the altitude difference between the Sun and the Moon at a calculated ‘best time’ to view the Moon plus the width of the crescent. More details of this method and maps displaying the Moon’s visibility are available here.

The new Moon in June will occur at 12:05am on Wednesday, June 17, i.e. just after midnight (all times are AEST, i.e. Sydney time). On June 17 the Sun will set at 4:53pm, and the Moon at 5:43pm. The lagtime is 50 minutes so the crescent Moon may be visible to the unaided eye. However, by the Yallop method, optical aid (binoculars for instance – but only use your binoculars after the sun has set) may be required to sight the Moon before it is visible to the unaided eye. On Thursday, June 18th, the Yallop method tells us that the Moon will be “easily visible to the unaided eye”.

The following new Moon (marking the end of Ramadan and thus the beginning of Eid-ul-Fitr) occurs on Thursday, July 16th at 11:24am. On July 16 the Sun will set at 5:05pm, and the Moon at 5:24pm. The lagtime is only 19 minutes so the crescent Moon will not be visible to the unaided eye, and the Yallop method concurs. On July 17, however, sunset is at 5:05pm and moonset is at 6:20pm so the lagtime is 75 minutes. The crescent Moon will be easily visible if the western sky is clear of cloud.

May 2015 night sky guide transcript and sky chart

Published by Melissa Hulbert on May 1, 2015 3 Comments

To help you learn about the southern night sky, Sydney Observatory provides a written guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory’s Astronomy Programs Coordinator.

Mel guides you to find the constellations, Orion, Scorpius and Crux (the Southern Cross), along with related ancient Greek and Australian Indigenous astronomical mythologies. She also helps you find some star clusters, including the Jewel Box. And she tells us what to look out for in the May skies.

There’s a lot happening in our sky this month, so read the transcript below for more details.

SEE THE SKY CHART
We provide an embedded sky map below (please be patient as it can take a little while to load) and a May 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.

BUY THE BOOK
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, 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 GUIDE (after the jump)

(more…)

Harry sees a Great Prominence Eject

Published by Andrew Jacob on April 15, 2015 No Comments

2015APR15.prom_3views

A Great Prominence Ejects, Sketch and copyright Harry Roberts ©, all rights reserved.

Regular solar observer & correspondent Harry Roberts reports on the ejection of a large prominence from the Sun’s limb.

Sun-watchers have lately been noting the meager prominences seen above the solar limb, hoping for a rerun of some SC23 ‘greats’ perhaps – and current filaments too have been mostly faint. It’s known that global solar fields are currently (mid-SC24) well below SC23 levels.

Thus, it was a happy surprise to see a huge prominence on the Sun’s NE limb on 2015 March 27 (March 26, 23:13UT). “Helio” timings were ‘run’ across its main footpoints (FP), as well as heights, and some of its complex detail was logged; but much fine structure was not recorded. “Helio” © Peter Meadows, soon showed the prominence stretched from lat. 13°N to 34°N, some 21 degrees. It was 87Mm at the highest point, above (FP) 2, the latter sited at +23,287.

This height, well above Zirin’s “50Mm limit” for large ‘quiescents’, implied the prominence was already ejecting. Yet close study and repeat timings showed no increase in height over the next hour – apart from some rearrangement of material mainly between FPs 2 and 4.

Such prominences are, in reality, large disc filaments seen above the limb, and are termed quiet region filaments (QRF): that is, they arise within ‘plumes’ or ‘streaks’ of decayed field trailing behind (i.e. following) areas of active spot formation. The streaks develop over several solar rotations and fields within them are only <100G in strength; i.e. they are long-lived but low power features. Perhaps longevity is the reason QRF grow so large. As the streaks form, they drift BOTH east and polewards; i.e. they drift NE in our example (Fig1).

This means that in Fig1 the right-hand side (i.e.N) parts of the prominence are likely well behind the solar limb (at Ln289) – perhaps 20° behind the limb (~Ln270°); indeed the fine detail of the prominence and its decreasing height towards the N suggests this. The highest point on the prominence was above FP2, presumably right on the limb, and declined northward. There was no major change in the structure when the session ended at 00:0UT.

Ejection? The structure was again studied (Fig2) at 05:46 on Mar 27UT (5h50m after Fig1), when changes were seen: but bigger ones had been expected. It was brighter and the tallest part of the feature now lay between FPs 3 and 4, where it was 98Mm high, and the ‘arch’ between them was wider and higher: no doubt the ejection was slowly underway. Yet the setting Sun’s altitude was (at 06:35UT) just 15°: with wind and poor seeing the session ended.

Fig3 is an enhanced ©GONG Halpha image made at the Udiapur station. The robotic ‘scopes do not track ejecta, and have a field of view (FOV) just 100Mm above the solar limb. At 11:50UT (12h15m after Fig1) we see the ejection is well advanced, with the main arch lifted mostly above the FOV (broken arrow), though some around FPs 1 and 4 is still attached.

Questions. Filaments are known to regenerate quickly, as the ejection removes the accumulated material but not the ‘filament channel’ nor the progenitor ‘streaks’ of old sunspot polarity. Yet, since the event, there has been no sign of filament regeneration at the site; perhaps in time?

What of its earlier life? My logs show a large but faint filament nearing the west limb on March 10 UT, a possible precursor, but cloud prevented viewing around the 13th when a big prominence may have decorated the NW limb. The site should return to the west limb around April 5: what will we then see?

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

21_Sunset_Nick LombThis morning at 9:45am AEDT the Sun crossed from the southern to the northern part of the sky. On this day daytime and nighttime are almost equal at 12 hours each. Daytime though is a little longer than 12 hours due to the size of the Sun’s disc and because the atmosphere bends the light from the Sun.

Post from the Australasian Skyguide, written by Dr Nick Lomb.

Sunset occurs when the top edge of the Sun appears to sink below the horizon. Photo Nick Lomb

Dancing Curtains of Light

Published by Melissa Hulbert on 3 Comments
Tags:

From the 13-17 March I was in Tromso, before heading further north for the eclipse. The 14th was the first chance of a clear night and friends and I joined an aurora chase out of Tromso into darker, hopefully clear skies. We were not disappointed. About 9pm soft auroral light started and then slowly intensified.

Dazzling curtains of light danced overhead on 14 March 2015.

Dazzling curtains of light danced overhead on 14 March 2015.

For the next few hours, dancing curtains of light gently swirled and moved above us and not only were we treated to the usual green and often red auroras but also purple and yellow.
The following night was unfortunately cloudy (it turns out the 14th and 15th were two of the best nights of the season until the activity of March 17, though this occurred during the daytime in Svalbard) but the night of the 16th was clear and we joined friends on a chase to Kvaloya. Upon arriving we immediate looked up and there again the dancing curtains of light were there. Although slightly fainter than the 14th, the purple and yellow colours in the auroras were stronger and along with these colours and the usual green and red, we also saw a deep turquoise blue from time to time.

Subtle purples and yellows were a feature of the aurora on 16 March 2015.

Subtle purples and yellows were a feature of the aurora on 16 March 2015.

Both nights have been a highlight of our Nordic adventure (along with a stunning solar eclipse yesterday) and something my friends and I agree we’ll never forget.

There are currently reverberations happening from the March 17th Coronal Mass Ejection (CME) and we hope to try for some Svalbard auroras tonight if the lovely (but cold, -26.6 degrees this morning) weather holds!

Aurora over Kvaloya on 16 March 2015.

Aurora over Kvaloya on 16 March 2015.

Search

About

The 'Observations' blog is run by the staff of Sydney Observatory which is located at Observatory Hill, The Rocks, in Sydney, Australia.

This site is for discussion purposes only and does not represent the official views of Sydney Observatory. Any views expressed on this website are those of the individual post author only. Sydney Observatory accepts no liability for the content of this site.

Please direct any correspondence about the content of the blog to:
observatory [at] phm.gov.au
and about web matters to:
web [at] phm.gov.au.