Meteors Over Japan
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What caused the fireballs that lit up the sky over Australia?
NT Emergency Services
Jonti Horner, University of Southern Queensland
Over the past few days a pair of spectacular fireballs have graced Australia’s skies.
The first, in the early hours of Monday, May 20, flashed across the Northern Territory, and was seen from both Tennant Creek and Alice Springs, more than 500km apart.
The second came two days later, streaking over South Australia and Victoria.
Such fireballs are not rare events, and serve as yet another reminder that Earth sits in a celestial shooting gallery. In addition to their spectacle, they hold the key to understanding the Solar system’s formation and history.
Crash, bang, boom!
On any clear night, if you gaze skyward long enough, you will see meteors. These flashes of light are the result of objects impacting on our planet’s atmosphere.
Read more:
Look up! Your guide to some of the best meteor showers for 2019
Specks of debris vaporise harmlessly in the atmosphere, 80-100km above our heads, all the time – about 100 tons of the stuff per day.
The larger the object, the more spectacular the flash. Where your typical meteor is caused by an object the size of a grain of dust (or, for a particularly bright one, a grain of rice), fireballs like those seen this week are caused by much larger bodies – the size of a grapefruit, a melon or even a car.
Such impacts are rarer than their tiny siblings because there are many more small objects in the Solar system than larger bodies.
Moving to still larger objects, you get truly spectacular but rare events like the incredible Chelyabinsk fireball in February 2013.
That was probably the largest impact on Earth for 100 years, and caused plenty of damage and injuries. It was the result of the explosion of an object 10,000 tonnes in mass, around 20 metres in diameter.
On longer timescales, the largest impacts are truly enormous. Some 66 million years ago, a comet or asteroid around 10km in diameter ploughed into what is now the Yucatan Peninsula, Mexico. The result? A crater some 200km across, and a mass extinction that included the dinosaurs.
Even that is not the largest impact Earth has experienced. Back in our planet’s youth, it was victim to a truly cataclysmic event, when it collided with an object the size of Mars.
When the dust and debris cleared, our once solitary planet was accompanied by the Moon.
Impacts that could threaten life on Earth are, thankfully, very rare. While scientists are actively searching to make sure no extinction-level impacts are coming in the near future, it really isn’t something we should lose too much sleep about.
Smaller impacts, like those seen earlier this week, come far more frequently – indeed, footage of another fireball was reported earlier this month over Illinois in the United States.
In other words, it is not that unusual to have two bright fireballs in the space of a couple of days over a country as vast as Australia.
Pristine relics of planet formation
These bright fireballs can be an incredible boon to our understanding of the formation and evolution of the Solar system. When an object is large enough, it is possible for fragments (or the whole thing) to penetrate the atmosphere intact, delivering a new meteorite to our planet’s surface.
Meteorites are incredibly valuable to scientists. They are celestial time capsules – relatively pristine fragments of asteroids and comets that formed when the Solar system was young.
Most meteorites we find have lain on Earth for long periods of time before their discovery. These are termed “finds” and while still valuable, are often degraded and weathered, chemically altered by our planet’s wet, warm environment.
By contrast, “falls” (meteorites whose fall has been observed and that are recovered within hours or days of the event) are far more precious. When we study their composition, we can be confident we are studying something ancient and pristine, rather than worrying that we’re seeing the effect of Earth’s influence.
Tracking the fireballs
For this reason, the Australian Desert Fireball Network has set up an enormous network of cameras across our vast continent. These cameras are designed to scour the skies, all night, every night, watching for fireballs like those seen earlier this week.
If we can observe such a fireball from multiple directions, we can triangulate its path, calculate its motion through the atmosphere, and work out whether it is likely to have dropped a meteorite. Using that data, we can even work out where to look.
In addition to these cameras, the project can make use of any data provided by people who saw the event. For that reason, the Fireballs team developed a free app, Fireballs in the Sky.
Read more:
How we solved the mystery of Libyan desert glass
It contains great information about fireballs and meteor showers, and has links to experiments tied into the national curriculum. More importantly, it also allows its users to submit their own fireball reports.
As for this week’s fireball over southern Australia, NASA says it was probably caused by an object the size of a small car. As for finding any remains, they are now likely lost in the waters of the Great Australian Bight.
NASA
Jonti Horner, Professor (Astrophysics), University of Southern Queensland
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Look up! Your guide to some of the best meteor showers for 2019
Flickr/Lukas Schlagenhauf, CC BY-ND
Jonti Horner, University of Southern Queensland and Tanya Hill, Museums Victoria
The year gets off to a bang with the Quadrantids, the first of the annual big three meteor showers. Active while the Moon is new, it gives northern hemisphere observers a show to enjoy during the cold nights of winter. Sadly, the shower is not visible from southern skies.
The other two members of the big three — the Perseids and Geminids — are not so fortunate this year, with moonlight set to interfere and reduce their spectacle.
So, with that in mind, where and when should you observe to make the best of 2019’s meteoric offerings? Here we present the likely highlights for this year – the showers most likely to put on a good show.
Read more:
Explainer: why meteors light up the night sky
We provide details of the full forecast activity period for each shower, and the forecast time of maximum. We also give sky charts, showing you where best to look, and give the theoretical peak rates that could be seen under ideal observing conditions – a number known as the Zenithal Hourly Rate, or ZHR.
It is important to note that the ZHR is the theoretical maximum number of meteors you would expect to see per hour for a given shower, unless it were to catch us by surprise with an unexpected outburst!
In reality, the rates you observe will be lower than the ZHR – but the clearer and darker your skies, and the higher the shower’s radiant in the sky, the closer you will come to this ideal value.
For any shower, to see the best rates, it is worth trying to find a good dark site (the darker the better) – far from streetlights and other illuminations. Once you’re outside, give your eyes plenty of time to adapt to the dark – half an hour should do the trick.
Showers that can only really be seen from one hemisphere or the other are denoted by either [N] or [S], while those that can be seen globally are marked as [N/S].
You can download this ics file and add to your calendar to stay informed on when the meteor showers are due.
Quadrantids [N]
Active: December 28 – January 12
Maximum: January 4, 2:20am UT = 2:20am GMT = 3:20am CET
ZHR: 120 (variable, can reach ~200)
Parent: It’s complicated (comet 96P/Macholz and asteroid 2003 EH1)
Despite being one of this year’s three most active annual showers, the Quadrantids are often overlooked and under-observed. This is probably the result of their peak falling during the depths of the northern hemisphere winter, when the weather is often less than ideal for meteor observations.
For most of the fortnight they are active, Quadrantid rates are very low (less than five per hour). The peak itself is very short and sharp, far more so than for the year’s other major showers. As a result, rates exceed a quarter of the maximum ZHR for a period of just eight hours, centred on the peak time.
Museums Victoria/Stellarium, Author provided
The Quadrantid radiant lies in the northern constellation Boötes, the Herdsman, and is circumpolar (never sets) for observers poleward of 40 degrees north. As a result, observers in northern Europe and Canada can see Quadrantids at any time of night. The radiant is highest in the sky (and the rates are best) in the hours after midnight.
For this reason, this year’s peak (at 2:20am UT) is best suited for observers in northern Europe – and given that peak rates can exceed 100 per hour, it is certainly worth setting the alarm for, to get up in the cold early hours, and watch the spectacle unfold.
NASA/MSFC/Meteoroid Environments Office/Danielle Moser and Bill Cooke, CC BY-NC
Alpha Centaurids [S]
Active: January 31 – February 20
Maximum: February 8, 1:00pm UT = February 8, 9pm (WA) = February 8, 11pm (QLD) = February 9, 12am (NSW/ACT/Vic/Tas)
ZHR: Variable; typically 6, but can exceed 25
Parent: Unknown
The Alpha Centaurids are a minor meteor shower, producing typical rates of just a few meteors per hour. But they are famed as a source of spectacular fireballs for southern hemisphere observers and so are worth keeping an eye out for in southern summer skies.
Alpha Centaurids are fast meteors, and are often bright. As with most showers that are only visible from the southern hemisphere, they remain poorly studied. Though typically yielding low rates, several outbursts have occurred where rates reached or exceeded 25 per hour.
The shower’s radiant lies close to the bright star Alpha Centauri – the closest naked-eye star to the Solar System and the third brightest star in the night sky.
Museums Victoria/Stellarium
Alpha Centauri is just 30 degrees from the south celestial pole. As a result, the radiant essentially never sets for observers across Australia. The best rates will be seen from late evening onward, as the radiant rises higher into the southern sky.
This year, the peak of the Alpha Centaurids coincides with the New Moon, making it an ideal time to check out this minor but fascinating shower.
Eta Aquariids [S preferred]
Active: April 19 – May 28
Maximum: May 6, 2pm UT = May 6, 10pm (WA) = May 7, 12am (QLD/NSW/ACT/Vic/Tas)
ZHR = 40+
Parent: Comet 1P/Halley
The Eta Aquariids are possibly the year’s most overlooked treat, particularly for observers in the southern hemisphere. The first of two annual showers produced by comet 1P/Halley, the Eta Aquariids produce excellent rates for a whole week around their peak.
The radiant rises in the early hours of the morning, after the forecast maximum time, and best rates are seen just as the sky starts to brighten with the light of dawn. It can be well worth rising early to observe them, as rates can climb as high as 40 to 50 meteors per hour before the brightening sky truncates the display.
Museums Victoria/Stellarium
Eta Aquariid meteors are fast and often bright, and the shower regularly rewards those who are willing to rise early. Spectacular Earth-grazing meteors that tear from one side of the sky to the other can be seen shortly after the radiant rises above the horizon.
This year conditions are ideal to observe the shower, with New Moon falling on May 4, just two days before the forecast maximum. As a result, the whole week around the peak will be suitable for morning observing sessions, giving observers plenty of opportunity to see the fall of tiny fragments of the most famous of comets.
Southern Delta Aquariids, Piscis Austrinids and Alpha Capricornids [N/S; S favoured]
Active: Early-July to Mid-August
Maximum: July 28 – 30
Combined ZHR: 35
Parent: Comet 96P/Macholz (Southern Delta Aquariids); Unknown (Piscis Austrinids); Comet 169P/NEAT (Alpha Capricornids)
In most years, the approach of August is heralded by keen meteor observers as the build up to the Perseids – the second of the year’s big three showers. This year, moonlight will interfere, spoiling them for most observers.
But this cloud comes with a silver lining. A fortnight or so before the peak of the Perseids, three relatively minor showers come together to provide an excellent mid-winter show for southern hemisphere observers. This year, the Moon is perfectly placed to allow their observation.
These three showers – the Southern Delta Aquariids, Alpha Capricornids and Pisces Austrinids – favour observers in the southern hemisphere, though they can also be observed from northern latitudes.
Regardless of your location, the best rates for these showers are seen in the hours after midnight. Reasonable rates begin to be visible for southern hemisphere observers as early as 10pm local time.
Museums Victoria/Stellarium
Museums Victoria/Stellarium
The Southern Delta Aquariids are the most active of the three, producing up to 25 fast, bright meteors per hour at their peak, which spans the five days centred on July 30.
The Alpha Capricornids, by contrast, produce lower rates typically contributing just five meteors per hour. But where the Southern Delta Aquariids are fast, the Alpha Capricornids are very slow meteors and are often spectacular.
Like the Alpha Centaurids, in February, they have a reputation for producing large numbers of spectacular fireballs. This tendency to produce meteors that are both very bright and also slow moving makes them an excellent target for astrophotographers, as well as naked-eye observers.
Flickr/Jeff Sullivan, CC BY-NC-ND
Taurids [N/S]
Active: September 10 – December 10
Maxima: October 10 (Southern Taurids); November 13 (Northern Taurids)
ZHR: 5 + 5
Parent: Comet 2P/Encke
The Taurids are probably the most fascinating of all the annual meteor showers. Though they only deliver relatively low rates (approximately five per hour from each of the two streams, north and south), they do so over an incredibly long period – three full months of activity.
In other words, the Earth spends a quarter of a year passing through the Taurid stream. In fact, we cross the stream again in June, when the meteors from the shower are lost due to it being exclusively visible in daylight.
So a third of our planet’s orbit is spent ploughing through a broad stream of debris, known as the Taurid stream. In total, the Taurid stream deposits more mass of meteoric material to our planet’s atmosphere than all of the other annual meteor showers combined.
So vast is the Taurid stream that there is speculation that it originated with the cataclysmic disintegration of a super-sized comet, thousands or tens of thousands of years in the past, and that the current shower is a relic of that ancient event.
Museums Victoria/Stellarium
Museums Victoria/Stellarium
Taurid meteors are slow, and are often spectacularly bright. Like the Alpha Capricornids, they have a reputation for producing regular fireballs, making them another good target for the budding astrophotographer.
Rather than having a single, sharp peak, Taurid activity stays at, or close to, peak rates for the best part of a month, between the maxima of the northern and southern streams, meaning that it is always possible to find some time when moonlight does not interfere to observe the shower.
Geminids [N/S]
Active: December 4 – December 17
Maximum: December 14, 6:40pm UT = December 15, 4:40am (QLD) = December 15, 5:40am (NSW/ACT/Vic/Tas)
ZHR: 140+
Parent: Asteroid 3200 Phaethon
Another of the big three annual meteor showers, the Geminids are probably the best, with peak rates in recent years exceeding 140 meteors per hour.
NASA/Lauren Harnett, CC BY-NC
The Geminids are visible from both hemispheres – although the radiant rises markedly earlier for northern observers. Even in the south of Australia, the radiant rises well before midnight, giving all observers the rest of the night to enjoy the spectacle.
Museums Victoria/Stellarium
Moonlight will seriously interfere with the peak of the shower this year, washing out the fainter meteors, with the result that observed rates will be lower than the ZHR might otherwise suggest.
But the shower regularly produces abundant bright meteors, and yields such high rates that it is still well worth checking out, even through the glare of the full Moon.
Ursids [N]
Active: December 17 – December 26
Maximum: December 23, 3:00am UT
ZHR: 10+
Parent: Comet 8P/Tuttle
The final shower of the year – the Ursids – is a treat for northern hemisphere observers alone. Much like the shower that started our journey through the year, the Quadrantids, the Ursids remain poorly observed, often lost to the bleak midwinter weather that plagues many northern latitudes.
But if skies are clear the Ursids are visible throughout the night, as their radiant lies just 12 degrees from the north celestial pole. As such, they make a tempting target for observers to check out in the evening, even if the radiant is at its highest in the early hours of the morning.
Most years, the Ursids are a relatively minor shower, with peak rates rarely exceeding ten meteors per hour. They have thrown up a few surprises over the past century, with occasional outbursts of moderately-fast meteors yielding rates up to, and in excess of, a hundred meteors per hour.
Museums Victoria/Stellarium
While no such outburst is predicted for 2019, the Ursids have proven to be a shower with a surprise or two left to show and so may just prove to be an exciting way to end the meteoric year.
If you have a good photo of any of this year’s meteor showers that you’d like to share with The Conversation’s readers then please send it to readerspic@theconversation.edu.au. Please include your full name and the location the photo (or any composite) was taken.
Jonti Horner, Professor (Astrophysics), University of Southern Queensland and Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Look up! Your guide to some of the best meteor showers for 2018
Flickr/David Meyer, CC BY-NC-ND
Jonti Horner, University of Southern Queensland and Tanya Hill, Museums Victoria
This year gets off to a relatively slow start when it comes to seeing the annual major meteor showers.
The Quadrantids, one of the big three annual showers, are lost to the vagaries of the full Moon in early January.
But the year’s other two most active annual showers – the Perseids (in August) and Geminids (in December) – are set to put on fine displays.
So when and where should you look to have the best chance of seeing nature’s fireworks?
Here we present the likely meteoric highlights of 2018. These are the meteor showers most likely to put on a good show this year.
Read more: Stars that vary in brightness shine in the oral traditions of Aboriginal Australians
For each shower, we give the forecast activity period and the predicted time of maximum. We also provide charts showing you where to look, and give the peak rates that could be seen under perfect conditions (known as the maximum Zenithal Hourly Rate, or ZHR).
The actual rate you see will always be lower than this value – but the higher a shower’s radiant in the sky and the darker the conditions, the closer the observed rate will get to this ideal value.
To see the best rates it is well worth trying to find a good dark site, far from street lights. Once outside, make sure to give your eyes plenty of time to adapt to the darkness (at least half an hour).
Showers that can only be seen from one hemisphere are denoted by either [N] or [S], with those that can be seen globally marked as [N/S].
Lyrids [N/S; N favoured]
Active: April 14-30
Maximum: April 22, 6pm UT = April 23, 2am AWST (WA) = 4am AEST (QLD/NSW/ACT/Vic/Tas)
ZHR: 18+
Parent: Comet C/1861 G1 (Thatcher)
The Lyrids hold the record for the shower with the longest recorded history, having been observed since at least 687BC.
That longevity is linked to the orbit of the Lyrid’s parent comet, discovered in 1861 by A. E. Thatcher. Comet Thatcher moves on a highly inclined, eccentric orbit, swinging through the inner Solar system every 415 years or so. Its most recent approach to Earth was in 1861.
Compared with many other comets, Thatcher’s orbit is relatively stable, as the only planet with which it can experience close encounters is Earth. This means the meteors it sheds continue to follow roughly the same orbit.
Over the millennia, that shed debris has spread all around the comet’s vast orbit, meaning that for thousands of years, every time Earth intersects Comet Thatcher’s orbit, the Lyrids have been seen, as regular as clockwork.
One study of the orbits of Lyrid meteors even suggests the shower may have been active for at least a million years.
Museums Victoria/stellarium
These days, the Lyrids are usually a moderately active shower, producing somewhere between 10 and 20 fast, bright meteors per hour at their peak. Occasionally, though, the Lyrids have thrown up a surprise, with rates climbing far higher for a period of several hours.
The best of those outbursts seem to occur every 60 years or so, with the most recent occurring in 1982 when observed rates reached or exceeded 90 per hour.
No such outburst is predicted for 2018, but even in quiet years, the Lyrids are still a fun shower to observe.
Museums Victoria/stellarium
They are best seen from northern latitudes, but their radiant is far enough south for observers throughout Australia to observe them in the hours before dawn.
For observers at mid-northern latitudes, the Lyrid radiant reaches suitable altitude by about 11pm local time. Viewers in the southern hemisphere have to wait until the early hours of the morning before reasonable rates can be observed.
The forecast time of maximum this year favours observers in Australia and east Asia but the timing of maximum has been known to vary somewhat, so observers around the globe will likely be keeping their eyes peeled, just in case!
Perseids [N]
Active: July 17 – August 24
Maximum: August 12, 8pm UT – August 13, 8am UT = from August 12, 9pm BST (UK) = 10pm CEST (Europe) = 6pm EDT (East Coast, US) = 3pm PDT (West Coast, US) for 12 hours
ZHR: 110
Parent: Comet 109P/Swift-Tuttle
For observers in the northern hemisphere, the Perseids are a spectacular summer highlight. At their peak, rates often reach or exceed 100 meteors per hour, and they are famed for their frequent spectacular fireballs.
The Perseids are probably the best known and most widely observed of all modern meteor showers. They are remarkably consistent, with peak rates usually visible for a couple of evenings, and fall in the middle of the northern hemisphere summer holiday season. The warm nights and frequent clear skies at that time of year make the shower a real favourite!
Like the Lyrids, the Perseids have a long and storied history, having been observed for at least 2,000 years. Their parent comet, 109P/Swift-Tuttle, is a behemoth, with the largest nucleus of the known periodic comets – some 26km in diameter.
It has likely moved on its current orbit for tens of thousands of years, all the time laying down the debris that gives us our annual Perseid extravaganza. It will next swing past Earth in 2126 when it will be a spectacular naked eye object.
Museums Victoria/stellarium
This year the forecast maximum for the Perseids favours observers in Europe, although given the length of peak activity, any location in the northern hemisphere has the potential to see a spectacular show on the night of August 12.
But don’t despair if it’s cloudy that night, as the Perseids have a relatively broad period of peak activity, meaning that good rates can be seen for a few days either side of their peak.
In 2018, the peak of the Perseid shower coincides with the New Moon, and so is totally unaffected by moonlight, which makes this an ideal year to observe the shower.
The further north you are, the earlier the shower’s radiant will be visible. But reasonable rates can typically be seen any time after about 10pm, local time. The later in the night you observe, the better the rates will be, as the radiant climbs higher into the sky.
It is not uncommon for enthusiastic observers to watch the shower until dawn on the night of maximum, seeing several hundred meteors in a single night.
Flickr/Michael Karrer, CC BY-NC
Draconids [N]
Active: October 6-10
Maximum: October 9, 12:10am UT = 1:10am BST (UK) = 2:10am CEST (Europe)
ZHR: 10+
Parent: Comet 21P/Giacobini-Zinner
The Draconids are a fascinating meteor shower, although in most years, somewhat underwhelming. Unlike the previous showers, the Draconids are a relatively young meteor shower that can vary dramatically from one year to the next.
First observed less than a century ago, the Draconids (also known as the Giaocobinids) are tied to a Jupiter-family comet called 21P/Giacobini-Zinner.
That comet was the first to be visited by a spacecraft, and has frequent close encounters with Jupiter, which continually nudges its orbit around. These encounters also perturb the meteor stream the comet is laying down, sometimes enhancing rates at Earth and sometimes diminishing them.
In the early 20th century, it was realised that Comet Giacobini-Zinner’s orbit comes close enough to Earth that we might be able to see meteors as we plough through the debris it leaves behind.
This led to the first predictions of Draconid activity. Sure enough, in 1920, the great meteor observer W. F. Denning confirmed the existence of the shower, with a mere five meteors observed between October 6 and October 9.
In 1933 and 1946, the Draconids produced two of the greatest meteor displays of the 20th century – great storms, with peak rates of several thousand meteors per hour. In those years, Earth crossed the comet’s orbit just a month or two after the comet passed through perihelion (closest approach to the Sun), and Earth ploughed through dense material in the comet’s wake.
After 1946, the Draconids went quiet, all but vanishing from our skies. Jupiter had swung the comet onto a less favourable orbit. Only a few Draconids were seen in 1972, then again in 1985 and 1998.
The late 1990s saw a renaissance in our ability to predict and understand meteor showers, born of enhanced activity exhibited by the Leonid meteor shower. Using the techniques developed to study the Leonids, astronomers predicted enhanced activity from the Draconids in 2011, and the predicted outburst duly occurred, with rates of around 300 meteors per hour being observed.
Museums Victoria/stellarium
This year comet Giacobini-Zinner once again passes through perihelion and swings close to Earth’s orbit. The chances are good that the shower will be active – albeit unlikely to produce a spectacular storm.
Modelling suggests that rates of 20 to 50 faint meteors per hour might be seen around 12:14am UT on October 9. Other models suggest that rates will peak about 45 minutes earlier, with lower rates of 15 to 20.
The Draconid radiant is circumpolar (that is, it never sets) for locations north of 44°N, and is highest in the sky before midnight. This year, the Moon is new at the time of the forecast peak, which is ideally timed for observers in Europe.
If skies are clear that evening, it is well worth heading out at around 11:30pm BST on October 8 (12:30am CEST on October 9) and spending a couple of hours staring north, just in case the Draconids put on another spectacular show.
Taurids [N/S]
Active: September 10 – December 10
Maxima: October 10 (Southern Taurids); November 12 (Northern Taurids)
ZHR: 5 + 5
Parent: Comet 2P/Encke
Of all the year’s meteor showers, the one that dumps the greatest amount of dust into Earth’s atmosphere are the Taurids. The inner Solar system contains a vast swathe of debris known as the Taurid stream. It is so spread out that Earth spends a quarter of the year passing through it.
In June, that debris spawns the Daytime Taurid meteor shower, which (as the name suggests) occurs during daylight hours, and is only really known thanks to radio observations.
After leaving the stream for a little while, Earth penetrates it again at the start of September, and activity continues right through until December. Hourly rates fluctuate up and down, with several distinct peaks and troughs through October and November.
The Taurid stream is complex – with at least two main components, known as the northern and southern branches. Typically, the Southern Taurids are active a little earlier in the year and reach their peak about a month before the northern branch.
Museums Victoria/stellarium
Museums Victoria/stellarium
The Taurids are slow meteors and feature plenty of bright fireballs. So even though their rates are low, they are well worth looking out for, particularly when other showers are also active, such as the Draconids, the Orionids and the Leonids.
Put together, these showers make the northern autumn or the southern spring a great time to get out and look for natural fireworks.
Orionids [N/S]
Active: October 2 – November 7
Maximum: October 21
ZHR: 20+
Parent: Comet 1P/Halley
Twice a year, Earth runs through the stream of debris littered around the orbit of Comet 1P/Halley. Throughout the month of October this gives rise to the Orionid meteor shower.
The Orionids are a fairly reliable meteor shower with a long, broad maximum. Typically, peak rates can last for almost a week, centred on the nominal maximum date. Throughout that week, Orionid rates can fluctuate markedly, leading to a number of distinct maxima and minima.
Orionid meteors are fast – much faster than the Taurids that are active at the same of year. Like the Taurids, they are often bright, the result of the high speed at which the meteoroids hit Earth’s atmosphere.
Museums Victoria/stellarium
Museums Victoria/stellarium
The Orionid radiant rises in the late evening and is only really high enough in the sky for reasonable rates to be seen after midnight. As a result, the best rates are usually observed in the hours before dawn.
This works well this year, as the Moon will be in its waxing gibbous phase, setting some time after midnight and leaving the sky dark, allowing us to watch for pieces of the most famous comet of them all.
Geminids [N/S]
Active: December 4-17
Maximum: December 14, 12:30pm UT = Australia: December 14, 8pm AWST (WA) = 10:30pm (QLD) = 11:30pm AEST (NSW/ACT/Vic/Tas) = United States: December 14, 7:30am (EST) = 5:30am (PST) = 2:30am (Hawaii)
ZHR: 120
Parent: Asteroid 3200 Phaethon
As the year comes to a close, we reach the most reliable and spectacular of the annual meteor showers – the Geminids. Unlike the Perseids and the Lyrids, which have graced our skies for thousands of years, the Geminids are a relatively new phenomenon.
They were first observed just 150 years ago, and through the first part of the 20th century were a relatively minor shower. But since then rates have improved decade-on-decade, to the point where they are now the best of the annual showers, bar none.
The reason for their rapid evolution is that their orbit (and that of their parent body, the asteroid Phaethon) is shifting rapidly over time, precessing around the Sun (wobbling like a slow spinning top). As it does so, the centre of Phaethon’s orbit, and the centre of the Geminid stream, are moving ever closer to Earth.
For northern locations, the radiant rises shortly after sunset, and good rates can be seen from mid-evening onwards. For observers in the southern hemisphere, the radiant rises later, so good rates are delayed until later at night (as detailed in our 2015 report on the shower).
Although the time of maximum this year seems to favour observers in the Americas and Australia, peak rates from the Geminids usually last around 24 hours, and so good rates should be visible around the globe.
This year the maximum falls a day before the Moon reaches first quarter so the best rates are visible (after midnight, local time) when the Moon will have set and moonlight will not interfere.
Museums Victoria/stellarium
Museums Victoria/stellarium
Given that rates from the Geminids continue to climb, the estimated ZHR of 120 is likely to be somewhat conservative. Rates in excess of 130, and even as high as 200 per hour, have been seen in recent years.
Geminids are medium-speed meteors and are often bright. The individual meteors also seem to last just that bit longer than other showers, a fact likely related to their parent object’s rocky nature.
Wherever you are on the planet, the Geminids are a fantastic way to bring the year to an end, and we will hopefully be treated to a magnificent display this year.
Jonti Horner, Vice Chancellor’s Senior Research Fellow, University of Southern Queensland and Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria
This article was originally published on The Conversation. Read the original article.
Look up! Your guide to some of the best meteor showers for 2016
Jonti Horner, University of Southern Queensland and Tanya Hill, Museum Victoria
Many meteor showers, caused by the Earth passing through streams of debris left behind by comets and asteroids, occur as regularly as clockwork, year on year. But whether you can see a great display in the night sky from a given shower varies from year to year, for a variety of reasons.
So what will be the highlights of the coming year, 2016?
Unfortunately, several of the year’s best showers (including the wonderful Geminids) will be wiped out by moonlight in 2016, so aren’t mentioned in this list. Fortunately, though, several good showers remain.
If a shower can only be seen from the northern hemisphere, we’ll denote that with an (N). For southern hemisphere showers, we’ll use (S), and for those visible from both hemispheres, we’ll use (N/S).
For each shower, the time of forecast maximum is given in Universal Time (UT), with conversions to local time for certain regions where the shower could be observed (such as the east to west coast of the US, or the east to west coast of Australia). For other regions where the shower is visible, simply convert from UT into your local timezone.
The Quadrantids (N)
Active: December 28, 2015 – January 12, 2016
Forecast Maximum: January 4, 8am UT = 3am EST (East Coast, US) = 12am PST (West Coast, US)
For observers in the northern hemisphere, the year starts with a bang. The Quadrantids are one of the year’s big three meteor showers, yielding rates that can exceed 100 or even 150 meteors per hour.
Unfortunately, their peak is very short, with rates only remaining above about a quarter of their peak for around a day. As a result of this, and the usually highly inclement winter weather in the northern hemisphere at Quadrantid peak, they are often overlooked.
The radiant of the shower is actually circumpolar for most of the northern hemisphere, so close to the pole that it never sets. For the same reason, the shower is impossible to observe from the southern hemisphere, where the radiant never rises.
Moonlight will not interfere with the Quadrantids in 2016. So, if skies are clear, it is possible that observers could see a great show. While Quadrantids can be seen at any time during the hours of darkness, the best rates are garnered in the morning hours, as the radiant rises higher into the sky before dawn.
A nice spectacle to start the new year.
The Eta Aquariids (S and low latitudes N)
Active: April 19, 2016 – May 28, 2016
Forecast Maximum: May 5, 8pm UT = May 6, 6am AEST (QLD/NSW/ACT/Vic/Tas) = May 6, 3am AWST (WA)
The Eta Aquariids are another shower best seen in the early hours of the morning. But they can be well worth setting your alarm early to observe.
Fragments of the most famous of comets, 1P/Halley, the Eta Aquariids are a broad meteor stream. It takes the Earth around six weeks to cross their full width.
The maximum occurs around May 5, and unlike the Quadrantids, the peak is broad. Rates often exceed 30 meteors per hour, in the hours before dawn, for over a week around the peak.
Museum Victoria/Stellarium
Eta Aquariids are fast meteors, hitting Earth’s atmosphere at 66km/s. They are often truly spectacular when seen shortly after the radiant rises, a few hours before dawn. These Earth-grazers often span the sky from horizon to horizon, leave lingering smoky trails, and are definitely an eye-catching sight.
The peak of the shower in 2016 occurs around the time of New Moon making it an ideal year to check out this enigmatic morning shower.
Piscis Austrinids, Southern Delta Aquariids and Alpha Capricornids (N/S)
Active: Late-July/Early-August
Forecast Maximum: July 28-30, 2016, around midnight local time
In the middle of the northern hemisphere summer, the attention of meteor observers usually turns to the Perseids, one of the highlights of the year. But a number of more minor showers are also active towards the end of July and start of August, and between them, they combine to give reasonable rates for observers in both hemispheres.
While the Perseids (which we’ll say more about in a moment) are best seen from northern skies, the Piscis Austrinids, Southern Delta Aquariids and Alpha Capricornids are visible across the globe and are actually easier to observe from the southern hemisphere than the north.
While each of the showers is relatively minor (at least compared to streams like the Perseids), they combine to yield 20 or 30 meteors per hour at their maxima, which all fall together in a cluster around the July 28-30.
Museum Victoria/Stellarium
The new moon falls on August 2, which means the maxima of these showers can be observed under dark skies, giving an ideal opportunity to check out these less well known showers.
Of the three showers, the Southern Delta Aquariids are the most active. They display several sub-maxima around July 26-31, reaching around 15 to 20 meteors per hour under perfect conditions.
The other two showers are weaker, perhaps yielding around five meteors per hour each at their peak (though they have occasionally exhibited higher rates). But the Alpha Capricornids have a reputation for producing bright, slow, spectacular fireballs, so are well worth looking out for.
The best viewing for these showers is around midnight, local time, though they can be seen for most of the night.
Museum Victoria/Stellarium
The Perseids (N)
Active: July 17, 2016 – August 24, 2016
Forecast Maximum: August 12, 1-4pm UT = 9am-12pm EDT (East Coast, US) = 6-9am PDT (West Coast, US) = 10pm-1am, August 13 JST (Japan)
The Perseids are only really accessible for observers in the northern hemisphere, but from there, they can be truly spectacular.
They occur in the middle of the northern hemisphere summer, during the school holidays there, and almost feel designed to get people interested in astronomy.
The Perseids are possibly the most easily accessible of the three big ones. Where the Geminids and Quadrantids occur in the often bitter depths of the northern winter, the Perseids are well suited to camping, and relaxation on a pleasant warm night.
The Perseid radiant reaches a useful altitude at around 10pm or 11pm, local time. From then on, conditions continue to improve through the early hours of the morning.
In any given year, at maximum, the Perseids can yield in excess of 100 meteors per hour. But 2016 could be unusually good. Calculations show that the Perseid debris stream has been nudged by the gravitational influence of Jupiter, bringing the densest part closer to Earth’s orbit.
As a result, Perseid rates promise to be particularly high. It is quite feasible that maximum rates could exceed 150 per hour.
In addition, 2016’s peak may feature several sub-maxima, as Earth passes through concentrations of dust laid down by the Perseid’s parent comet, 109P/Swift-Tuttle, during previous perihelion passages.
This is particularly important for observers in Europe. On the night of August 11 and morning of August 12, it is likely that these enhanced rates might reach, or even surpass, the number of meteors to be seen at the traditional time of maximum, which falls some 14 hours later.
Wherever you are in the northern hemisphere, the nights of August 11 and 12 are a prime time to watch for the Perseids. Perseids are fast meteors, often bright and eye-catching, and make a good excuse for a camping trip.
The Ursids (N)
Active: December 17 – 26, 2016
Forecast Maximum: December 22, 9am UT = 4am EST (East Coast, US) = 1am PST (West Coast, US) = 6pm JST (Japan)
Moonlight unfortunately interferes with the maxima of all the main meteor showers of the final third of the year, washing out the peaks of the Orionids, the Leonids and the Geminids.
At the very end of 2016, however, comes a northern-hemisphere-only shower that is often overlooked, the Ursids. Ursid meteors radiate from a point just 14 degrees from the north celestial pole.
As a result, their radiant is circumpolar (never sets) for all locations north of a latitude of 14 degrees. The further north you live, the higher the radiant sits in the sky, meaning that Ursid meteors can be observed throughout the hours of darkness.
Museum Victoria/Stellarium
The Ursids occur at the northern-hemisphere mid-winter. This results in the unusual situation that it is possible for people in the Arctic Circle to observe a meteor shower in the middle of the day.
In most years, the Ursids are only a moderately active shower. Around maximum, rates usually reach just about ten per hour. But on a couple of occasions in the past 50 years, the Ursids have produced outbursts, with rates reaching or exceeding 50 per hour.
Given how poorly observed and characterised the Ursids are, it may well be that several other such outbursts were missed. Indeed, there have certainly been several other years in which observed rates were moderately higher than usual.
While no outburst is explicitly forecast for this year, the Ursid meteor shower could prove a very nice way to end another year of meteor observing.
For more information on the meteor showers throughout 2016, check out the International Meteor Organisation’s 2016 meteor calendar.
Jonti Horner, Vice Chancellor’s Senior Research Fellow, University of Southern Queensland and Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museum Victoria
This article was originally published on The Conversation. Read the original article.
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