Get Ready for the Geminid Meteor Shower overnight this Friday/Saturday

As usual at this time of the year, the Earth is entering a stream of debris from rock comet 3200 Phaethon, which is the source of the annual Geminid meteor shower. Forecasters expect the shower to peak on Dec. 13-14 with as many as 120 meteors per hour.

This year the nearly full Moon will reduce the number of meteors you may see but it is still well worth a look. Expected to peak from about midnight Friday Australian Eastern Daylight Time (or 1300 UT) until 9pm (1000 UT) Saturday, this meteor shower will be visible in both hemispheres.

Though you do need to keep in mind that meteor showers often peak hours before or after predictions and for sure we certainly don’t know everything that a given meteor stream might have in store!

This shower is an interesting one though, with an equally interesting history and source. The Geminids were first identified as a distinct meteor shower by R.P. Greg of Manchester UK in 1862, and the estimated ZHR rose from about 20 to 80 through the 20th century. The parent source of this shower remained unknown until 1983, when astronomer Fred Whipple linked them to the strange “rock-comet” body 3200 Phaethon. This is an Apollo asteroid also thought to be a member of the Pallas family of asteroids, 3200 Phaethon seems to be shedding enough material to produce the annual Geminid meteor shower. This makes the annual shower rare as one not produced by a comet. It’s worth noting that 3200 Phaethon also passes extremely close – 0.14 AU – from the Sun at perihelion, and gets periodically “baked” during each 1.4 year passage.

In the 21st century, rates for the Geminids have stayed above a Zenith hourly rate (ZHR) of 120, now the highest of any annual shower. It’s worth noting that an extrapolated ZHR of almost 200 were seen in 2011 when the Moon was at an equally unfavorable waning gibbous phase! The Geminids always produce lots of fireballs, capable of being seen even under moonlit skies.

With our warmer nights down under it is a great time to get out and have a look! Jupiter is also looking good after about 10:30pm and Mars and Saturn are visible in the early dawn skies as well.

An update on Comet ISON!

The comet had been visible in the Southern Hemisphere before passing the Sun but since the 19th November it has been very difficult to see as it has risen just before the Sun. After it had passed the Sun it would be rising just after the Sun rise and setting before the Sun set, in the southern hemisphere so hence we would not have been able to see it.

At around 6:44am our time this morning the comet reached perihelion (its closest approach to the Sun) where it broke up and then something continues on – it might just be gravel and dust or there might stay a chunk of rock big enough to stay comet like. But now only time will tell if it is big.  This goes to prove that although we certainly know a lot more about comets than we did before – there is a lot more that we do not know.  Many have pronounced Comet ISON as already being dead and it certainly will not reach the brightness and spectacular display that had been predicted – but as Mark Twain is often quoted: “Rumours of my demise are greatly exaggerated.”  Something emerged from the sun after Comet ISON made its closest approach today. Is it ISON? Both professional and amateur astronomers are analysing images from NASA satellites to learn more about comet’s fate. Northern ground based observers may have to wait until around the 9/10 of December now to see if there is anything to see. But they will not get the amazing views that we were all hoping for.

However, at every single opportunity it could find, Comet ISON has done completely the opposite of what was expected, and it certainly wouldn’t be out of character for this dynamic object to yet again do something remarkable. Even if the comet broke up, it offered a very rare opportunity to see how one of the oldest objects in the solar system interacted with the Sun’s magnetic field and its behaviour in the sun’s magnetic field will help scientists understand more about both comets and the Sun. This  was the first comet in recorded history which has come from so far away and passed so close to the sun, passing the sun at a distance of around 1.6 million kms that has been so well-studied and observed.

So we wait and see, this has been one of the most well observed, followed and commented in social media worldwide. A fleet of spacecraft watched ISON plunge toward the sun, including NASA’s STEREO satellite, the European Space Agency/NASA SOHO spacecraft and the Solar Dynamics Observatory. The Hubble Space Telescope should be able to take a close look in a couple of weeks if it did indeed survive.

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The photograph above is from the NASA SOHO Space Telescope’s LASCO C3 camera showing a fragment emerging from the other side of the Sun about 3 hours after perihelion.

The picture below is taken this at 00:42UT 1 December 2013 and shows the remnants of the comet as it leaves the SOHO LASCO C# camera’s field of view.

Comet ISON

There has been a lot of interest in the Comet 2012/S1 (ISON), more commonly known as Comet ISON. This comet has been predicted to become the comet of the century; this of course, may not eventuate. For those of us fortunate to have witnessed C/2006 P1 (McNaught) in January 2007 it will sure take a lot of beating.

The comet was discovered on 24 September, 2012, by two amateur astronomers in Belarus and Russia, using a 40-cm (16-inch) telescope. As it took them a day to confirm that the object was a comet, the organisation International Scientific Optical Network with which they are associated was credited with the discovery.

Over the past decade, hundreds of sungrazing comets have been discovered, but they are usually small, short-lived, and only seen by spacecraft designed to observe the Sun. Most sungrazing comets do not survive their trip around the Sun as they are disrupted by its intense radiation and gravity. Most of these, however, are quite small being only tens of metres across. The nucleus of Comet Ison is believed to be around 4km in diameter and hopefully its larger size will insulate the interior from the Sun’s energy.

One reason this is considered to be such an interesting comet is that it is believed to be making its first approach to the inner solar system. Along with this belief, comes the reason for all the uncertainty in the predictions as scientists can only guess at how bright it will become at the time it is closest to the Sun. There will be professional and amateur astronomers eagerly observing the comet from the ground and via the internet as a whole fleet of spacecraft have turned their cameras in its direction.

The comet has been gradually brightening as it speeds up on its journey towards the Sun. Unfortunately for us in the Southern Hemisphere just before and just after it passes behind the Sun on November 29, it will be below the horizon in both the morning and evening sky. This is the time that the comet is most likely to be at it brightest. For northern hemisphere observers, at these times, it may even be naked eye or perhaps visible in binoculars. A few weeks later the comet’s outward trajectory, providing it survives its passage around the Sun, will bring it to just 0.4 times the distance from the Earth to the Sun.

But perhaps, the greatest unknown is, in fact whether or not the comet will actually survive its passage through the corona which is the Sun’s atmosphere. At the time it passes the Sun it will only 1.1 million kms away and the nucleus of the comet will be subject to a combination of both extreme heating approximately 5000 degrees Celsius, which is hot enough to melt iron as well as constant radiation bombardment.  Add to that the fact that the Sun’s strong gravitational pull will be trying to tear it apart. Still the best guess from scientists is that the nucleus or at least a large chunk of it will manage to sweep around the Sun and start making its way out of the solar system.

Comets are believed to be the frozen left-overs from the formation of our Solar System, originating in the Oort cloud. While comets have been in a deep freeze for the past 4 billion years, planets and asteroids have changed a lot from their original compositions. Better understanding of their ices, dust, and organic matter, and how they have changed over the past billions of years, tell us about the origins of our Sun, the planets, and, possibly, life on Earth. To astronomers, every bright comet is an opportunity to learn more about our Solar System.

 NOTE that it is always dangerous to look directly at the Sun. Do not use telescopes or binoculars to search for the comet, just your unaided eyes and block the Sun with a post or other convenient object. Take extreme care!

 

Eta Aquarid Meteor Shower May 3-6

Just a reminder that the Eta Aquarid meteor shower will peak this weekend and into early next week, this shower is associated with Halley’s Comet.

The Moon will be a very slim crescent by the time the Eta’s peak on the morning of the 6th May (Monday).

It is advisable that you try to observe at least the morning before and after the peak as the maxima is very broad for this shower and it is quite possible that rates can vary.

The expected Zenith Hourly Rate is around 65 meteors per hour, but realistically this may be much lower, this shower has shown good rates in the past.

Best observing time is from around 3:30am.
The meteors will appear to “radiate” away from the star Eta Aquarii, meteors closer to the radiant will appear much shorter and ones further away will leave longer streaks, of which you can trace the origin back to the radiant.
Any meteor NOT tracing back to the radiant is classified as “sporadic” or could be a member of another shower which might be showing activity.
Some meteors near the radiant will show as a rapid pinpoint flash of light indicating a “head-on” meteor, don’t worry they won’t hit you!

Look for fast (65km/sec) white/yellowish coloured meteors which leave a 2 to 3 second “train” (sometimes longer), ie: the streak left over after the meteor “burns” out.

There will be some early morning International Space Station passes in the NE on the morning of the peak (6th May) at around 4:21am but will keep low (17 degrees) above the horizon!

Thanks to my pal – Chris Wyatt for the reminder and chart!

Lyrids Meteor Shower, peakings around tonight April 23rd.

Head out early tomorrow morning between midnight and dawn to catch the Lyrids Meteor Shower.

The Lyrids radiant is close to the constellation of Lyra (a harp). The constellation rises just after midnight in the southern hemisphere and moves across the northern sky. The Lyrids meteor shower is best viewed after midnight o well before sunrise on 23/24th April. Point your feet towards the northern sky and look about 45 degrees above the horizon. You should see a really bright white star there – this is the blue white star Vega. This shower is caused by the Earth’s atmosphere passing through the dusty pebbly debris left over from Comet Thatcher and has been known to produce spectacular meteors.

So what is a meteor? As a comet (which is a large ball of rock and ice from the outer Solar System) passes by the Sun they become quite heated up and they begin to shed gas, ice, dust particles and rocks which we see as the comets tail. This is left behind as the comet continues on its journey around the Sun.  If the comet’s orbit intersects that of the Earth’s orbit some of material strikes our atmosphere and we see a meteor.

Comet Thatcher also known was discovered by an American amateur astronomer A.E. Thatcher in 1861. This comet was the brightest in over half a century and both head and tail were visible together in broad daylight. Every spring for at least the past 2,700 years, Earth has passed through the trail, thrilling countless sky watchers with the sight of flaming dust and grit. In 1803, it was reported that it looked as if the entire sky was alight with flaming stars.

The Lyrid meteors strike our atmosphere about 95 kilometres above the earth and at speeds of around 49 km/sec or 175,000km per hour and can burn up in some pretty amazing fireballs.

Typical meteoroids which is the name given to meteors before they hit the atmosphere – range in size from grains of sand to walnuts. The bigger they are, the brighter. A meteor that actually hits the ground – a rare event fortunately is called a meteorite.

So if you want to have a look –  find somewhere away from street  lights and other bright lights where you can see clearly to the north and east. head out early in the morning either just after midnight – although the Moon will make it harder to see some of the dimmer meteors o around about  3:30 to 5 a.m. toting a thermos of hot chocolate, tea or coffee. Make sure you’re suitably rugged up for the weather and get yourself all comfy in a reclining lawn chair, banana lounge or under a blanket or sleeping bag. No special equipment required.  Look towards the North and enjoy the beauty of the early morning sky and see how man meteors you can see.

“SuperMoon” this Sunday

The biggest and brightest full moon of the year arrives tomorrow as our largest natural or otherwise satellite comes a little closer than normal. It will, at least from our perspective on Earth appear a bit bigger – a good experiment – take a photo tonight and take one next full moon in the same place and see if it is true.

The term ‘Supermoon’ is a nickname for a perigee full moon, this is the when the Moon is  closer to the Earth than usual in its orbit. Apogee and perigee refer to the distance from the Earth to the moon. Apogee is the furthest point from the earth while Perigee is the closest point to the earth and it is in this stage that the moon appears larger. Looking at the moon in the sky without anything to compare it to, you wouldn’t notice any size difference. But the difference in size can in fact be quite significant.

full moon at apogee and perigee

If you were to take a picture when the Moon is at perigee and again at apogee using the same camera and lens you would notice the difference.

The full Moon occurs at 1:35pm (AEST) Sunday May 6th in Australia. It is predicted that the moon will about 14 per cent brighter than usual.

Sunday’s event is a “supermoon,” the closest and the biggest and brightest full moon of the year. At 1.35 p.m., the moon will be about 356,956 km from Earth. That’s about 24,653 km closer than it is on average.

That proximity will make the moon appear about 14 percent bigger than it would if the moon were at its farthest distance, however, the difference in appearance is so small that you will find it hard pick it with your unaided eye.

The moon’s distance from Earth varies because it follows an elliptical orbit not a circular one.

Like any full moon, tomorrow’s moon will look bigger when it’s on or near the horizon rather than higher in the sky, thanks to an optical illusion. The full moon appears on the horizon at sunset. On the East coast, for example, that will be a at 5.07pm.

The last “supermoon” on March 20, last year was about 380 km closer than this year’s will be. Next year’s will be even a bit farther away than this year’s. Each year there is a perigee and an apogee Moon and the distances vary.

One effect that can be noticed doesn’t affect me where I live, but coastal folks are very familiar with the tides and how their height varies over the course of a month, again, due to the Moon not always being the same distance from the Earth. As the Moon’s orbit brings it in closer proximity to our planet, its gravitational forces can increase by almost 50%, and this stronger force leads to high tides. Likewise, when the Moon is farther away from the Earth the tides are far less spectacular.

The Moon’s influence can also be balanced out by the position of the Sun – if the Sun and the Moon find themselves 90 degrees apart in relation to an observer on the Earth, then high tides are not as high as they normally would be. This is because despite its greater distance from the planet, the Sun’s mass allows it to exert enough gravitational force on the oceans that it can negate some of the effects of the Moon’s pull. This phenomenon of lower high tides is called a neap tide. In the same way, when the Sun lines up with the Moon and the Earth, as during a Full Moon, then the Sun can act to amplify the tidal forces, drawing even higher tides. These are known as spring tides, named not for the season, but for the fact that the water “springs” higher than normal. The variance in the height of the world’s tides also depends on the local geography of the coastline and the topography of the ocean floor.

Eta Aquarids Meteor Shower May 5/6 2012

The Eta Aquarid meteor shower is the first of two showers that occur each year as a result of Earth passing through dust released by Halley’s Comet, with the second being the Orionids.  The point from where the Eta Aquarid meteors appear to radiate is located within the constellation Aquarius. This shower definitely favours the Southern Hemisphere observer as they

Created in Stellarium - finder for the eta aquarids

are usually a lightish meteor shower producing about 10 meteors per hour at their peak in the Northern Hemisphere but can peak at around 40-50 per hour here in the Southern hemisphere in a dark sky. The shower’s peak usually occurs on May 5 & 6, however this shower tends to have a broad maximum so viewing should be good on any morning from May 4 – 7.

The full moon which occurs on May 6th will probably ruin the show this year, washing out all but the brightest meteors with its glare.

But still worth having a look if you are up, to see how many Eta Aquarids can be seen in the moonlit sky. For the most part, this is a pre dawn shower. The radiant for this shower appears in the east-south-east at about 4 a.m. local time (wherever you are) and the hour or two before dawn usually offers the most meteors.

Try for a photo of Jupiter, Venus and the crescent Moon tongiht

A month ago, Venus, Jupiter and the crescent Moon were nicely for evening sky watchers around the world. Tonight it’s happening again. Tonight the three will form a bright triangle in the western sky at sunset afte around 7pm.

See Jupiter, Venus and the Crescent Moon form a lovely traingle tonight

25th Anniversary of SN1987a

This February marks the 25th anniversary of the discovery of Supernova 1987A.  A star, in the Tarantula Nebula within the Large Magellanic Cloud (LMC), called Sanduleak 69 202, exploded and became a supernova back on 24th February 1987.

It is now 25 years since the light from this cosmic explosion first reached us here on Earth. The star itself actually exploded about 168,000 years before, of course, with the light taking that long to reach us.

SN1987A has become the most studied star remnant in history and has provided great insights into supernovae and their remnants. It has some interesting connections to the Anglo-Australian Observatory and Siding Spring and is still being studied to this day.

SN 1987A was discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24, 1987, and within the same 24 hours independently by Albert Jones in New Zealand. On March 4–12, 1987 it was observed from space by Astron, the largest ultraviolet space telescope of that time. Hubble had yet to be launched.

On February 23rd, approximately three hours before the visible light from SN1987A reached the Earth, a burst of neutrinos was observed at separate neutrino observatories around the globe. This is likely due to neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface).

At 7:35 a.m. Universal time, Kamiokande II detected 11 antineutrinos, IMB 8 antineutrinos and Baksan 5 antineutrinos, in a burst lasting less than 13 seconds. Even though, the actual neutrino count was only 24, this was a significant rise from the previously-observed background level. This was the first time neutrinos emitted from a supernova had been observed directly, and marked the beginning of what is now ‘neutrino astronomy’.

The Supernova exploded in the Tarantula Nebula area near the edge of the Large Magellan Cloud – a satellite galaxy to our own. Even though its location in the LMC meant it was 10 times more distant than if it had been in our own Milky Way, it also meant that we had a relatively unobscured view of the supernova and its environment; there was never any ambiguity about its distance; and the fact that it lies so far south meant that observations could be done each night throughout the first year as it was always visible at some time during the night.

SN1987A was the brightest and closest supernova that has been seen since the invention of the telescope back in 1604. That supernova was called “Kepler’s Star” and the supernova was in our own galaxy around 20,000 light years away. It was so bright that it outshone Venus and Jupiter and was even visible in daylight for 3 weeks back then. The only other one in our own galaxy was “Tycho’s Star” seen in 1572 and also visible to the naked eye. There have only been a total of 8 naked eye supernova that are known.

SN1987 was also It was able to be seen quite easily with the naked eye, despite not even being in our own Milky Way galaxy. Visible for some months afterwards, it was easy to find and exciting to point out to others this bright new star in the LMC. 

SN1987A provided some significant opportunities  specific to the decade that followed and which came about as a direct result of the supernova discovery. These include the development of infrared instrumentation and spectropolarimetry which were evolving rapidly at the AAT and elsewhere. At the time of the supernova, photographic film was still in use at observatories and the internet did not yet exist. All discovery communications were done by telex between the various observatories around the world.

Data was shipped on large tapes back across to England and the other observatories to be reduced and analysed.

Even the introduction of CCDs, with their great sensitivity and dynamic range, made a major difference during the first few years. But much more importantly, the Hubble Space Telescope became available not long after the explosion.  We would have learned a lot less about SN1987A had it occurred a decade earlier, and there is unfortunately no guarantee that we will have any HST-like capability even 10 years from now.

Pioneer Astrophotographer,  David Malin, was working at the Anglo-Australian Telescope at the time of SN 1987A’s first sighting and was able to take several images of the light echoes of the supernova. One of his images is shown below.

Although the AAT observing schedule had been fully assigned for the semester through to June , when SN1987A erupted, data was able to be obtained on almost two thirds of the nights, and those observations took up 16% of the total time available. This was achieved by using up all the engineering, service and director’s time, as well as, requiring each observer to give up one hour per night of their time to allow observations with whatever instrument was on the telescope. The observers willingly co-operated and so much incredible data was able to be collected.

The emphasis was on observations that could best utilise the 3.9m aperture of the AAT or observations which best used the available instrumentation unique to that telescope: for example, speckle interferometry and spectro-polarimetry.

The Anglo-Australian Telescope was ideally situated as it was the only telescope from which the supernova was accessible and which had the necessary instrumentation to make the observations. Even though there were some changes necessary to the existing IPCs based spectro-polarimeter which was optimised for observing much fainter object.

 Data was collected by the non-optimised instrument 4 days after the discovery and it was found that the instrument issues meant that data accuracy would be impacted. So over the next 10 days the engineers worked to modify the instrument to use CCDs as detectors and the first observations with were made on March 7th, a mere 2 weeks after the supernova was first seen.

One particular highlight was the very rapid construction, by Peter Gillingham, of a temporary Littrow spectrograph, which had a resolving power of almost one million, which  was able to be used to study interstellar lines. It was available within 2 months of the Supernova. It has been called the  “wooden spectrograph”.

The new CCD spectropolarimeter – was built up from the RGO spectrograph  plus Pockels cell plus IPCS which itself was a well proven set-up. In order to make it all work with incredibly bright object – the instrument was modified to use the CCD detectors. This raised further hurdles which were one by one overcome and they were able to collect over the next 12 months the first ever spectropolarimetry data on a supernova.

A common-user version of this very successful Ultra-High Resolution  Spectrograph  (UHRF) was later  commissioned and operates on the telescope to this day. Peter Gillingham was able to very quickly come up with a temporary version of a coude mounted spectrograph by combining a novel Littrow lens design with one of the gratings that was eventually destined for use on the UCLES instrument. It was the success of this project which meant they were able to obtain funds to later build the new instrument.  The original instrument was first housed in a large wooden box.

 The AAT was perfectly placed geographically and so was able to get onto observing this supernova very quickly. It has now been observed for many years and the campaign in radio, infra-red and optical continue to this day since 25 years is a long time to us – but rather infinitesimal in the scale of the universe.

So was it just luck? Being in the right place at the right time?

Personally, I don’t think so – I think it was having this amazing instrument up here at Siding Spring and a really innovative group of staff who were able to think outside the box and design instruments and obtain data on this incredible supernova explosion in a very short space of time. Luck may have been the SN going off nearby – but skill and dedication was what made all the difference.

 

SN1987a before and after by David Malin Anglo-Australian Telescope - used with permission

This photograph shows the field around the site of the supernova in great detail, both before the supernova exploded (right) and about 10 days afterwards, when it was still brightening. The image of the star that exploded to create the supernova is elongated. This does not necessarily indicate any peculiarity or a close companion, rather it is the effect of stars being by chance aligned along the line of sight. Several other examples can be seen in this picture and other, different, blended images are seen in the photograph of the same field taken two weeks after the supernova appeared (left). The pre-supernova plates were taken over about 90 minutes on the night of 1984 February 5, centred on the Tarantula nebula. The post-supernova plates (LHS image) were exposed for a total of about an hour on the night of 1987 March 8.

 The difference in image quality (‘seeing’) between these pictures is an effect of the Earth’s atmosphere which was much steadier when the plates used to make the pre-supernova picture were taken. Top left is NE. Width of each image is about 8 arc minutes. Text and Image © 1989-2010, Australian Astronomical Observatory, photograph by David Malin.

 

 

Planetary Alignments in the Evening Sky

Over the next 4 weeks, the solar system’s brightest planets will be putting on a spectacular evening show as they start to move into formation over the nights to come.

If you go out just after sunset and look towards the west, you will see Venus and Jupiter popping out of the twilight even before the sky has gone completely dark. After you have found them once or twice you will be able to find them earlier.   Seeing these two brilliant planets surrounded by darkening blue of the evening sky is a lovely sight.

If you go out at the next night, the view improves, because Venus and Jupiter are converging.  In mid-February they were about 20 degrees apart but by the end of the month, the angle narrows to only 10 degrees—so close that you can hide them together behind your outstretched palm.  Their combined beauty grows each night as the distance between them shrinks.

 A special night to look is Saturday, February 25th, when the crescent Moon moves in to form a slender heavenly triangle with Venus, Jupiter and the Moon as its vertices.  One night later, on Sunday, February 26th, it happens again.  This arrangement will be visible all around the world, from city and countryside alike.  The Moon, Venus and Jupiter are the brightest objects in the night sky; together they can shine through city lights, fog, and even some clouds.

 After hopping from Venus to Jupiter in late February, the Moon exits stage left, but the show is far from over.

 In March, Venus and Jupiter continue their relentless convergence until, on March 12th and 13th, the duo lie only three degrees apart—a spectacular double beacon in the sunset sky. Now you’ll be able to hide them together behind a pair of outstretched fingertips.

 There’s something mesmerizing about stars and planets bunched together in this way. This strange phenomenon is due to the fact that your eye works in much the same way as a digital camera does. In front, there is a lens which focuses the light and the retina acts like a photo-array behind the lens to capture the image of what you see. The retina is made up of rods and cones which are the organic equivalent of electronic pixels.

 There’s a tiny patch of tissue near the centre of the retina where cones are extra-densely packed. This is called “the fovea.” This enables you to see objects in high definition – it is critical to everyday tasks such as reading, driving and watching television. The fovea has the brain’s attention.

 The field of view of the fovea is only about five degrees wide. Most nights in March, Venus and Jupiter will fit within that narrow cone.  And when they do—presto!  It’s spellbinding astronomy.