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.
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)
Geoffrey Hargrave : MAAS Collection object P2903-9/17. Gift of William Hudson Shaw, 1974.
On the ANZAC weekend and through to the 24th May Sydney Observatory is turning back the clock, and changing our latitude and longitude in the planetarium to recreate the sky as it appeared to the troops as they landed at Anzac Cove. We will watch the Southern Cross sink in the South and then the Moon set in the West. We will notice the stars in the dark sky, until the sun rises and reveals the steep landscape over the beach. Find out about Sydney Observatory’s connection to the Gallipoli landings through the story of Geoffrey Hargrave told by curator Debbie Rudder.
1:05pm Planetarium: Sky tonight and sky over Gallipoli on ANZAC Day (weekends only)
2:30pm Planetarium: Sky tonight and sky over Gallipoli on ANZAC Day
All tours are 30mins and include a visit to a telescope dome.
Tour cost: $10 adult, $8 conc, $26 family
Members: $8 adult, $6 conc, $22 family
Visitors to the National Trusts S.H. Irvin Gallery special exhibition ‘Your friend the enemy’ are admitted half price with voucher.
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.
This 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
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.
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.
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.
Today dawned cold (-24 degrees), bright and clear and we headed off early on snowmobiles to a remote area away from Longyearbyen. High on the mountain at Fjordnibba, overlooking Tempelfjorden was the perfect place to observe the eclipse from.
Fjordnibba, our observing site for today’s solar eclipse.
The partial phases passed quickly and as the diamond ring approached, amazing shadow bands were seen across the snow. Totality once again passed all too quickly and the second diamond ring signalled the end of totality. To be in such an amazing, remote and wonderful place with crystal clear skies and watching the twilight at totality lighting the mountains has made this one of the most memorable eclipses I have seen.
Widefield image of Totality. Venus is visible in the top right of the image.
Diamond Ring, just before totality.
I’m currently sitting in a well heated room, snow and ice along the window, overlooking an icy fjord. Where am I? I’m at latitude 78 degrees north on the island of Svalbard where the temperature outside is now a balmy -15 degrees. Thousands of astronomers and umbraphiles have descended here to witness one of the most spectacular natural wonders, a total solar eclipse. After two days of cloud, today dawned bright and clear, in fact, today is only the third day the Sun has been seen here since it returned to the sky on 24 February. We are all hoping Mother Nature will be kind enough to provide another stunning day tomorrow for the eclipse.
Total Lunar Eclipse
Saturday 4 April 2015, 9pm – midnight.
VIEW OUR LIVE STREAM OF THE LUNAR ECLIPSE HERE
VIEW LUNAR ECLIPSE FEED FROM GRIFFITHS OBSERVATORY HERE
VIEW LINKS TO LIVE FEED FROM SLOOH
Download this Fact Sheet for details about timing: April 2015 Total Lunar Eclipse Fact Sheet
Lunar Eclipse photo by Geoff Wyatt, 8 October 2014
Lunar Eclipse Live
Sydney Observatory is well placed to view the April lunar eclipse which appears in our north-eastern sky. Sydney Observatory will be live streaming the total Lunar Eclipse. Dr Andrew Jacob, curator of astronomy , will be at Sydney Observatory directing the live feed from 9pm to 11:30pm local time (10-12:30 UT) from our 16-inch north-dome telescope. Here is your YouTube link. Whilst waiting for the eclipse you can hear Astronomy guide, Brenan Dew, explain the Lunar Eclipse and Aboriginal Astronomer, Willy Stevens, discuss how his people explained Moon phenomenon.
Total Lunar Eclipse Event
Saturday 4 April
9pm – midnight
THIS EVENT IS GOING AHEAD USING LIVE FEEDS FROM OTHER SITES AND HOPING FOR AN IMPROVEMENT IN THE WEATHER.
If you have booked and want to cancel please email email@example.com before the event starts.
We are running an event on-site which focuses on telescope viewing of the eclipse and information sessions. Snacks, tea, coffee and hot chocolate available on site. Because it is a late night this is suggested for ages 15 and over. Cost: $59 family, $22 adult, $15 child; members $48 family $18 adult $12 child. Concessions $18. Bookings and pre-payments are essential. BOOK ONLINE NOW! For enquiries please call 9921 3485.
Media Enquiries only please call 9921 3485/ 9921 3484 or 0411137102.
Even if you can’t visit Sydney Observatory during the Total Lunar eclipse keep in touch and lets us know about your eclipse experience via Sydney Observatory Facebook or @sydneyobs Twitter.
Melissa Hulbert, Sydney Observatory, took this image of Moon in eclipse showing the spectacular red colour.
The full Moon reddened during the total lunar eclipse of October 8 2014. Image copyright Geoff Wyatt.
Lunar eclipse 28 August 2007, photos and animation by Geoffrey Wyatt
Total lunar eclipses
Dr Nick Lomb, Sydney Observatory’s consultant astronomer and curator, and Sarah Reeves, astronomy guide, provided the following helpful explanation. On average there is an eclipse of the Moon every eight months, with a little under half of these total. The actual number of lunar eclipses in a year can range from none to a maximum of three. A total eclipse of the Moon is visible from Australia on average every 2.8 years. In Australia, a total lunar eclipse will occur on 4 April 2015. In parts of the Northern Hemisphere there will also be a total lunar eclipse on 27 September 2015.
Why the Moon is red during a total eclipse
The Moon will appear red during totality because red light from the Sun is bent by the Earth’s atmosphere onto the Moon. The light is red as other colours such as blue are scattered in all directions leaving red, just as at sunset. Another way of putting it is that seen from the Moon the Earth is dark, but surrounded by an atmosphere lit up by either by sunset or dawn. Whether the Moon will go red and how dark a red depends on atmospheric conditions at the time of the eclipse. This post about the 2007 total lunar eclipse will give you some idea of what we can hope to see on the night.
How do eclipses occur?
Eclipses of the Moon occur when the Moon moves into the shadow of the Earth. There are three kinds of lunar eclipse – penumbral, partial and total. Penumbral eclipses occur when the Moon falls in Earth’s penumbra (the fainter part of our shadow). A partial eclipse occurs when a portion of the Moon is covered by the Earth’s umbra (the darkest part of our shadow), and a total eclipse occurs when the entire Moon is inside the Earth’s umbra. When the Moon is fully immersed in the dark part of the shadow we see a total eclipse of the Moon. At such times the eclipsed Moon usually takes on a dark reddish colour from the light bent or refracted onto the Moon by the Earth’s atmosphere. When the Moon is only partially immersed in the dark part of the shadow we have a partial eclipse.
How eclipses of both the Sun and Moon occur. Sketch Nick Lomb
An eclipse of the Moon can only happen at full Moon phase. It does not happen every month as the path the Moon takes around the Earth is tilted by about 5° to the path the Earth takes around the Sun. Hence at full Moon the Earth’s shadow usually falls below or above the Moon.
What is the history of Moon eclipses?
Eclipses of the Moon first provided proof that the Earth is a globe as the edge of the Earth’s shadow moving across the Moon is always part of a circle. This was noticed by the Greek philosopher Aristotle who lived in the fourth century before our era. According to ancient Chinese legend an eclipse of the Moon occurs when a dragon begins eating the Moon. Hence the tradition in China during eclipses was to make as much noise as possible by banging on drums and pots to scare away the dragon. This technique has so far succeeded on each occasion.
Viewing a lunar eclipse
Unlike solar eclipses, a lunar eclipse can be seen from anywhere that is experiencing nighttime when the eclipse occurs. Lunar eclipses are also safe to view with no special eye protection, and fun to photograph. For those who missed last October’s event, you won’t have to wait too long – the next total lunar eclipse is due to occur on 4 April 2015.
Check out our free monthly sky guides including podcast, sky map and transcription, giving you a guide to highlights in the night sky for each month of the year.
Check out also our free Moon phase calendar.
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Image courtesy of Delft University of Technology via wikipedia.org/wiki/Pi_Day
That’s right! Today is the day that we celebrate the mathematical constant π (Pi) – 3.141592653589793232384626433…
But why is today Pi Day? Because… if you write the date in the MM/DD format, today is 03/14 and 3.14 are the first three digits of the irrational number that is the ratio of a circles circumference to its diameter. That is: π. But things are even better for π day this year, because in the MM/DD/YY format, this year is 03/14/15, which is π to 5 significant figures: 3.1415. If you want to be even more meticulous, wait until 9.26 (am or pm) and 54 seconds (if rounding up) to get an even bigger dose of π. At this instant the date and time will be: 3/14/15, 9:26:54, which is π to 10 significant figures: 3.141592654! This is as good as mathematical dates can get!
But wait there’s more! Today is not the only day that we can celebrate π in the calendar year, because in just 130 days time it will be π approximation day, or the 22/7 (DD/MM), which as a fraction is a common approximation of this irrational number π.
This post was written by Brenan Dew, Astronomy Guide at MAAS – Sydney Observatory