The movement of the setting Sun along the horizon from just before to just after the autumn equinox. The date and the azimuth in degrees (measured eastwards from north) is marked. Diagram Nick Lomb
In 2014 the autumn equinox is on Friday 21 March when the Sun crosses from the southern to the northern part of the sky. On this occasion the exact time the Sun is on the dividing line between the two hemispheres is 3:57 am.
We often refer to the Sun as rising in the east and as setting in the west. This is not strictly true as during the year each time the Sun rises or sets it does so in a slightly different spot on the horizon. It is only during the equinoxes, spring and autumn, that it rises due east and sets due west. At other times it sets, for example, south of west during the summer half of the year and sets north of west during the winter half of the year. The setting south reaches furthest south on the summer solstice, 22 December in 2014, and furthest north on the winter solstice, 21 June in 2014.
At the solstices the position of the setting Sun along the horizon changes very little from day to day. This slow movement is reflected in the meaning of the word ‘solstice’ as it means ‘the day the Sun stands still’.
In contrast, at the equinoxes, half way between the two solstices, the setting Sun shifts position on the western horizon at a rapid rate, the fastest rate during the year. This is illustrated in the animated drawing above that shows as seen from Sydney the setting Sun shifts position at the rate of one degree along the horizon every two days. As the Sun subtends half a degree width in the sky, its daily shift is equivalent to its own width at this time of the year.
Of course, this shift along the horizon could form the basis of a yearly calendar. Ancient civilisations needed a calendar so that they would know when to plant crops and when to expect harvest so it seems likely that they would have utilised such observations for the purpose of a calendar. Stonehenge has long been suggested as having had a calendar function with gaps between the stones providing observing spots to match the setting or rising Sun to features on the horizon. Chankillo in Peru with 13 evenly-spaced towers running north-south on a low hill is a more certain example of such a calendar based on the changes in the position of the rising and setting Sun.
If you have a reasonable view towards the east and the rising Sun or the west and the setting Sun try observing the shift yourself. Observe from the same spot and either note where the Sun rises or sets on each date or photograph it from the same spot just as it sets. Of course, looking directly at the Sun is dangerous, take care and do not look at it directly.
Urbain Leverrier, the French astronomer who predicted the existence and position of the planet Neptune, was born on this day in 1811. Like the Englishman John Couch Adams, Leverrier based his calculations on slight discrepancies in the motion of the then newly discovered planet Uranus.
The statue of Urbain Leverrier outside Paris Observatory. Image Nick Lomb
The giant planet Jupiter is shining brightly in the northern sky each evening. It is still very bright as it was only in early January when it was at opposition, that is, in the opposite direction to the Sun as seen from Earth. Tonight we have the fine sight of the gibbous Moon near Jupiter; it is above and to the left or west of the planet.
Jupiter and the Moon on the morning of 11 March 2014. Chart Nick Lomb
Tomorrow is the anniversary of the birth of Soviet cosmonaut Yuri Gagarin in 1934. At the age of 27 he became the first human in space when he circled the Earth for one hour 48 minutes in the Vostok 1 spacecraft. Sadly, in 1968 Gagarin died in a plane crash while retraining as a fighter pilot.
The Gagarin Memorial in Star City, outside Moscow. Photo Nick Lomb
In the early evening the Southern Cross, the smallest constellation in the sky, is fairly high in the south-eastern sky. At least two of the five stars of the cross have companion stars. A small telescope shows the brightest star, Acrux, as double, but it is harder to see the companion or companions of the second brightest star, Beta Crucis.
The Southern Cross. Photo Nick Lomb
At the Cosmos preview. Observatory manager, Toner Stevenson, Neil deGrasse Tyson and MAAS director of public engagement Michael Parry. Photo © Powerhouse Museum, Sydney.
On the night of Sunday 16 February superstar astrophysicist Neil deGrasse Tyson hosted a special ‘After Dark’ tour at Sydney Observatory. Thirty lucky viewers of the National Geographic Channel had an exclusive 90-minute tour with Tyson, visiting the 3D theatre, planetarium and our 140-year old telescope. Observatory guide, Tracy Getts, and Andrew Jacob helped out.
Tyson is a masterful science communicator. Despite the rain on the night he kept his audience enthralled with his enthusiastic style, an uncompromising devotion to science and his mastery of science story-telling. Although Tyson is the Director of the enormous Hayden Planetarium in New York he appreciated the intimate and interactive nature of the new Sydney Planetarium, our cosy, fireside planetarium.
But why was Neil deGrasse Tyson in Sydney? He was here to promote the new series ‘Cosmos: A Spacetime Odyssey’. This is a ‘reboot’ of Carl Sagan’s memorable and influential Cosmos series first screened over thirty years ago.
The new series begins on the National Geographic Channel on March 16 but in the meantime you can see the trailer. A few Observatory staff were lucky enough to preview episode #1 the following night. I can’t wait to see the rest if the series. It looks epic and grand and I hope it achieves its aim to “awaken the broadest possible audience to the wonders of the universe, as revealed by the scientific perspective.”
Space rock or asteroid 11947 Kimclijsters circles the Sun between the paths of Mars and Jupiter. Named after Belgian tennis player Kim Clijsters, sometimes known as “Aussie Kim”, the asteroid is at its closest to Earth for the year at the very safe distance of 417 million km.
Kim Clijsters playing on 18 February 2007. Image (width cropped) courtesy Flickr and Stijn Audooren
The president of the IDA, Jim Dougherty, at Melbourne Observatory on Monday 3 March 2014. Photo Nick Lomb
The president of the International Dark Sky Association (IDA), Jim Dougherty, has made a quick visit to Australia. On Monday he met people concerned about light pollution in Melbourne and on Tuesday in Sydney, visiting the Observatory.
IDA is an international organisation involved in educating people about the night sky and night time lighting. It has worked with lighting manufacturers to encourage them to make light fittings that shine light only where it is needed and not into the sky or into people’s eyes causing glare.
Jim, an environmental lawyer by profession, is keen to change the public mindset about night time lighting: more is not better. He says that outdoor lighting uses seven per cent of all power generated and that two-thirds of that is wasted light going up into the sky. Just by reducing the amount of wasted light a significant saving could be made in energy usage with a consequent reduction in carbon pollution levels.
Hopefully, the visit of the IDA president will reinvigorate the fight against light pollution in Australia. There are already a few groups and people involved in this work such as SOLIS in Sydney and OLIS in Melbourne, but there maybe the opportunity to form a local chapter of the IDA and to attract new, keen and active people.
A view of the brightly lit office buildings near Circular Quay in Sydney as seen from the Opera House. Photo Nick Lomb
There is a considerable need to become more active about light pollution as it is not only a problem for astronomers. Light at night disrupt wildlife, for example by making it much harder for nocturnal animals to hide from predators. As well, insects are attracted to lights and become an easy feed for birds, so that there are fewer insects left to fertilise plants and hence there are effects on the whole ecosystem.
Most importantly, research studies indicate that night time lighting can disrupt people’s circadian rhythms with potentially serious health consequences. The American Medical Association said in 2012 that “Low levels of illuminance in the blue or white fluorescent spectrum disrupt melatonin secretion”. And that health effects include “potential carcinogenic effects related to melatonin suppression, especially breast cancer”. Further that “Other diseases that may be exacerbated by circadian disruption include obesity, diabetes, depression and mood disorders, and reproductive problems”. Note that it is blue light that causes the most damage.
As an example of urgent problems, Ausgrid, which supplies electricity over much of the Sydney area and beyond, in August 2013 reported on a trial of new LED streetlights in quiet pedestrian streets at a number of sites in the Sydney metropolitan area. Each of the trial lights from three different manufacturers had a blue colour (~5000K colour temperature). It seems to me that Ausgrid has neither knowledge nor interest in the potential serious health effects of these lights on the occupants of the houses on either side of these suburban streets. With the “success” of the trials, Ausgrid is ready to sell the idea of these blue-rich street lights to local councils and to start rolling out their installation as a replacement for any failed old-style street lights.
As Jim Dougherty says there needs to be a complete mindset change in the community about night time lighting. And it needs to happen as soon as possible.
The map maker Gerard Mercator was born on this day in 1512 in Flanders, which is now part of Belgium. Mercator is known for developing a cylindrical projection for maps in which lines of constant compass direction are represented by straight lines.
A Mercator projection of part of the globe. Courtesy Wikimedia Commons and Strebe
The Sun observed in white light at 10 am AEDT on the morning of 4 March 2014. Sunspot group AR11990 is prominent directly above the centre of the Sun. Photo Nick Lomb
For aging actors, they say, the lure of the stage is irresistible: so it can be for aging ‘super’ spots!
On January 2, AR11944 emerged as a giant group of SC24, hosting a GOES X1.2 flare and many M-class during its transit. Farewelled on Jan 13 we asked: would it return? It did.
In late Jan it returned as a Hale class Delta group – the old (p) spot of earlier group 11944 was now ‘jammed’ against the (f) spot of a large new dipole. The amalgam was dubbed AR11967 and hosted many M-class flares during its 14 days on transit (earlier report). This time we noted the short lives of Delta groups, suggesting no return performance.
AR11990: Wrong this time! Recall that the old (p) spot was the sole survivor of January’s Delta group, 11944. Feb 24(UT) saw the remnant (p) spot, once again, rounding the eastern limb!
The returned spot, now AR11990, and other groups on the disc were logged until 00:03 Feb 25(UT), when viewing ended and positional calculations began. A glance at the GOES flux and a call from ML 60 minutes later, saw the ‘scope hastily set-up again: one of the largest flares of SC24 was in progress!
Four views of the X-class flare from AR11990 on 25 February 2014. Sketch and copyright Harry Roberts ©, all rights reserved
X4.9 Flare: the peak of this great flare had been missed (00:49), but when first viewed at 01:04 was still at X2.3 – and showed extensive flare ribbons (visual 3B) splashed across the eastern limb at the ‘returnee’ site. This was the largest flare the writer has seen in SC24 and a most impressive sight – reminiscent of some great flares of SC23. Six logs of the event were made and four are shown (Fig).
In E-W extent the flare ribbons crossed some 20º of longitude – even passing behind the east limb: perhaps reflecting the extent of the earlier groups that had arisen at the sites. In fact 11990 seemed to lie at the centre of the big flare. Ribbons also spread south from the big spot along a filament channel there.
Several surges were noted. Fig 3 shows one (S2) projecting upwards to the limb. Figs 3 and 4 show post flare loops developing.
The old (p) spot of 11994 had had strong red field (up to 2700G) during its first two transits – red being the current polarity for preceding (i.e. p) spots in southern groups. However, after its earlier ‘collision’ with the new dipole to its west (AR11967) it now had one large penumbra with the original red umbra plus a remnant of violet from the 11967 encounter.
So it’s now a Delta group in its own right – while (almost) all following and preceding lesser spots seem to have gone. What caused such a big flare in what is now a modest sunspot?
Relic Fields: Areas of activity on the Sun may be highly localised – indeed, Schrijver and Zwaan speculate that the solar tachocline [the transition region between the solid rotating interior and the differential rotating exterior regions of the Sun - ed] may ‘store’ magnetic flux for long periods, releasing new flux from time to time: activity nests. The ‘old’ (p) spot site, at –14,106, is presumably such a place.
Zirin refers to persistent filaments that may host ‘spotless’ flares long after a Delta group has faded away. And Belgium researcher, J. Janssens, recently remarked:
It’s interesting to see that the two strongest flares (of SC24 so far) were produced at the same location on the Sun (+17º,300º), but in different sunspot regions separated 8 months in time.
Note in Fig 1 that bright faculae was sited at longitude 123º, some 16º ahead of the old (p) spot, where the (p) spot of the earlier dipole (11967) was sited – faculae that stretched back to the ‘old’ survivor. Several filaments also crossed this area of relic fields.
CME: A spectacular mass ejection emerged above the Lasco instrument’s occulting disc ~40m after the flare- an impressive ejection velocity of about 400km/sec.
Finally, we may ask if the ‘old’ (p) spot of AR11944 has finally ‘run its course’ – was the big flare due to a last rearranging of fields at the site – or might we see further dramas in days to come?
Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.