The Cassini spacecraft captured this breathtaking view of Saturn on May 4th 2014 but I just noticed it today.
Cassini captured this view at a distance of approximately 2 million miles (3 million kilometers) from Saturn using a near infrared filter. Cassini was high above the ring plane and this is a view of the planet we never get from Earth. From our position near the centre of the solar system Saturn (and most of the planets beyond Earth) look fully illuminated all of the time.
One of the features that immediately catches the eye is that hexagon shape around the north pole of Saturn. The hexagon at Saturn's north pole isn't a new feature. It was seen in images taken by the Voyager 1 and 2 probes back in the 1980s.
Here are some closer Cassini views of it:
For some sense of scale: each side of the hexagon is a bit wider than the Earth.
Saturn is a rapidly rotating gas giant planet. How can a regular and seemingly long-lived feature like this arise in the atmosphere of Saturn? Astronomers don't have the definitive explanation yet although there is experimental evidence from laboratories on Earth which might give a clue.
The video shows an experiment to simulate conditions that might lead to a regular structure being set up in the atmosphere of Saturn. They built a cylindrical tank capable of varying the fluid flow within concentric regions inside. A hexagon appeared at the chaotic boundary between fluids moving at very different speeds. A number of vortices formed in the region separating the fluid flow and distributed themselves evenly around the pole at centre. Why a hexagon? Actually the experimenters could fine tune the spin rates to produce a hexagon but they could also generate other regular polygons too. You can see some them here.
The experiment showed how stability and order could arise from chaotic conditions induced by large differences in wind speeds at different latitudes on Saturn. There are still questions to be answered. For instance why is there no comparable feature at the south pole of Saturn? There is a huge, long-lived storm at the south pole, but no polygonal structure.
I love trawling through the raw image section of the Cassini website. It can lead to serious distraction no matter if they're images of the rings, the moons or Saturn itself. But I'm aware that this mission won't last forever; Cassini's time is running out and sometime in 2017 NASA scientists will place it in a final series of orbits which will send it crashing into Saturn.
Just bought a new Microsoft Surface 3. The (happy happy) days when I had to install the operating system myself are gone but I still have to put the software on.
Given that the resources are limited to 128GB (for the moment) on the tablet itself I can only really install stuff I absolutely need. So, this is a list of stuff that I can't get by without. Geek alert!
Absolutely must install SkyTools 3 too to record my observations at the telescope. I have installation disks but no CD drive so it'll have to wait for now.
I could happily survive without Microsoft Office but everyone else seems to use it. So therefore I have to. An unhappy situation. Space is tight on the tablet so I won't be installing Open Office alongside it.
Just put the finishing touches to a planetary elongation chart. Here it is in all of its glory:
A high quality PDF can be downloaded here.
This chart shows the positions of the naked-eye planets to the east (left) or west (right) of the Sun. The vertical axis represents the days and months of the year. The diagonal bands represent constellation boundaries. The wavy yellow band is a region close to the Sun in which it would be difficult to observe the planets. This chart behaves like a game of PacMan; any planets reaching opposition 180 degrees west of the Sun wrap straight over to the evening sky on the far left. Think of this as being like an unwrapped cylinder!
The places where the paths of the planets intersect represent conjunctions. These are visually striking opportunities to see bright planets shining together in the sky. In 2015 there are at least 12 such opportunities.
There's a particularly striking gathering of the planets in the morning sky during October 2015. The planets Mercury, Venus, Mars and Jupiter will all appear together before sunrise on many of those autumn mornings.
Here's a star chart showing the northwards drift of the comet during the first weeks of 2015.
I've left the magnitude estimates off the chart but astronomers are expecting Comet Lovejoy to be around 6th, maybe even 5th magnitude during this period. That will put it within easy reach of binoculars and small telescopes. From especially dark sites it might attain naked eye visibility.
Comet Lovejoy is very well placed for UK astronomers in the New Year. After beginning the month close to the southern horizon in the early evening sky it rapidly climbs north from Lepus (the Hare) through Eridanus (the River) and into Taurus (the Bull).
Just a bit of background on the comet itself. It was discovered by veteran comet hunter Terry Lovejoy in August 2014 and was his 5th comet discovery. This one is going to reach a similar brightness to one of his previous comets - 2013 R1 - which was visible in the UK in late Autumn 2013.
2014 Q2 Lovejoy will be closest to Earth (0.469 AU / 43.6 million miles) on January 7th. It will reach a perihelion (closest to the Sun) distance of 1.29 AU (119.9 million miles) on January 30th. The entire orbit of this comet lies outside Earth's orbit and that's why the comet can be seen almost on the opposite side of the sky to the Sun despite being near perihelion.
I'll post updates on Comet 2014 Q2 Lovejoy and, hopefully, some pictures over the coming weeks.
A PDF finder chart is available here.
I've been spying the Intergalactic Wanderer recently through the telescope. That's a much more poetic name than NGC 2419, which how astronomers officially catalogue it.
I took a picture of it last year with my usual setup: Nikon D80 at prime focus of a Celestron 4 inch refractor.
That fuzzy ball at the centre is one of the Milky Way's largest, most massive globular clusters. It contains twice as many stars as Omega Centauri and perhaps five times the number of stars found in the "Great" Hercules Globular Cluster, M13. In other words - the Wanderer is huge. Only its vast distance makes it look unimpressive through small telescopes.
Here's a clearer picture of it.
The Intergalactic Wanderer is about 300,000 light-years away. That's almost twice the distance of the Large Magellanic Cloud (the largest satellite galaxy of the Milky Way). In fact the "Wanderer" title was conferred when astronomers though the cluster might not be part of the Milky Way. Now, astronomers realise that the Wanderer does indeed orbit the centre of the Milky Way but it takes around 3 billion years to do so.
Despite it's relative obscurity - even amongst amateur astronomers - this faint fuzzy has gained some degree of recognition through its appearance on a frequently shared Facebook meme:
...which probably has more than a grain of truth in it.
It's mostly work, work, work with a dash of astronomy. I'm writing end of semester exams for the two maths modules I teach. I'm fine tuning some booklets of maths practice problems for the students to take away over the Christmas period. I spent a few hours last weekend writing an online test for Monday morning...but the computers all crashed when the students came to do it. So I'm hastily writing a replacement to do next Monday instead. On top of that I'm fixing some explanations and problems in the previous version of my maths book; there are a lot of things I need to improve about the textbook since I started teaching some of the topics - like Functions - this year. On Friday I've got an astronomy event with NASTRO at Bamburgh. Not sure what I'm going to talk about at that. Lots of young astronomers expected so I want it to be interactive. Over and out :-)
Early evening March 17th 2002 I had my telescope set up in the garden just outside the house. It was still twilight but it was dark enough to see the constellations: the brightest stars of Gemini, Taurus and Orion were easily visible. Jupiter and Saturn were also shining and very high in the sky. Then I noticed a bright new star in the sky not far from Jupiter. For a moment I thought it was a satellite but then realised that it didn’t look like it was moving. My next thought was that it might be a new supernova! I got the telescope – a 10 inch Dobsonian – on to the new star very quickly.
The view through the eyepiece was unusual; it was disk shaped – a bit like Jupiter – but bigger and with a brighter core at the centre. Through the eyepiece it did actually appear to be slowly moving. At this point I realised that I was probably watching a rocket from beneath and looking directly into the exhaust.
I watched for a few minutes and then went to get the digital camera. I’d taken a few shots of the moon before, by holding it to the eyepiece. No control over the exposure or flash but I was hopeful I’d get something. Returning to the telescope I watched in amazement as the disk seemed to shatter into hundreds of pieces and disperse. I took this picture:
Two of the pieces seemed more substantial and I watched them for a few more minutes as they slowly drifted apart. I was always curious about what rocket I actually saw there and why it ended up in pieces like that.
So having found the picture again recently I saw that the date and time was stored in the image properties! I googled the date and found that the GRACE mission was launched that day.
GRACE was launched atop a Rokot launch vehicle from Russia earlier that day so I initially thought I’d seen the separation of the individual satellites. I tried to find a way of confirming whether GRACE was visible from the UK on the day of launch. After a bit of digging I found a paper which seemed to confirm that various manoeuvres had to take place in the within visibility of several ground stations. The path of the satellite (shown in the paper) would have made it visible from the UK.
So….a minor mystery solved. I’m not sure I saw the actual separation of the satellites from the rocket – that was supposed to happen 90 minutes or so after launch (I was watching many hours later). It was probably a burn to separate or correct the separation of the satellites. I’m happy to have what may be one of the few pictures of the start of this incredible mission!
The dark evenings of November provide a great opportunity to view the Milky Way as it flows through the northern constellations of Cassiopeia and Perseus. There are so many star clusters to see! As a young astronomer 30 years ago, I remember looking with binoculars from my bedroom window and discovering a nice semi-circle of stars below a brighter star. The view is shown in the large red circle below.
This scattered cluster of stars was not listed in any of the deepsky object catalogues that I knew about (Messier, New General Catalogue) and it was many years until I discovered that this object had a name. The bright star at the focus of the semicircle is called Mirfak (or alpha Perseii) and the cluster of stars is called the “alpha Persei Moving Cluster“. It is also known as Cr39; it is the 39th entry in a catalogue compiled by the Swedish astronomer Per Collinder in 1931. It also goes by the name Melotte 20.
So what is it? Well “cluster” is too strong a word. Astronomers call this an “association” instead. The stars are more loosely gravitationally bound than a cluster and the stars may eventually go their separate ways. For now, they’re all moving in roughly the same direction through space.
The cluster is approximately 600 light-years away from us and the 50 or so stars are mostly massive, very hot blue-white stars. The exception is the brightest member, Mirfak, which is slightly cooler and more yellowish. The age of the stars is estimated to be about 70 million years. Binoculars show the cluster very well; telescopes have a field of view just a bit too big to do this group of stars justice.
There are many other clusters of stars to be found in this part of the sky. Just go outside with your binoculars and take a look for yourself!
Week 5 on the course was devoted to the mid-term exams in all the academic subjects; so no lectures or seminars.
In Week 6 we got stuck into more algebraic tools and methods; namely polynomial division, factor theorem and remainder theorem. Read on for more details.
The Taurid meteor shower reaches peaks on November 3rd and again on the 12th. For many amateur astronomers the month of November is associated with the Leonids - a much more famous shower which has occasional stormy outbursts. But I have to say, I prefer the Taurids because they have a more interesting backstory!
About 20,000 to 30,000 years ago a huge comet - perhaps 50 km in diameter or more - became embroiled in a series of close approaches to the planet Jupiter. Nothing unusual about that - Jupiter has a huge family of comets even today and we;ve seen first hand how Jupiter can change comet orbits and even tear comets apart.
These days, all we have left of the original giant progenitor comet is a small, faint comet with an orbital period of 3.3 years (called Encke's Comet) and a complex series of dust streams which the Earth encounters in November each year. The dust released by the fragmented nuclei over periods of thousands of years have gradually been spread out into a broad swathe of the inner solar system. Actually, the Earth also encounters one of the streams during June but during the daylight hours. It is speculated that the devastating Tunguska event of 1908 was due to a larger fragment disintegrating in the Earth's atmosphere. That's another story.
On Earth, each November, we see the remains of a giant comet, streaking into our atmosphere as a shower of shooting stars and appearing to come from the constellation Taurus. It takes the Earth weeks to cross these lanes of dust and in doing so we encounter two distinct peaks - evidence of the complex evolution of the meteor orbits. So in November we see the Northern Taurids near the start of the month and and the Southern Taurids around two weeks later. Activity is fairly low - typically about seven or eight per hour. Compare this to, say, the short sharp spike in activity of the Perseids in August or the Geminids in December.
Will we see another giant comet? Interestingly, there is evidence to suggest a big comet, seen in our skies in 1106, broke apart and the sun-grazing fragments have produced several of the best comets of past millennium.
There's also the possibility that a swarm of Kreutz sungrazing comets (probable fragments of the Great Comet of 1106) are en-route to the inner solar system and will arrive in the coming decades. If true then there are good prospects of seeing another Great Comet (or Comets).
So, no major showers this month. But chances are good this month that if you spend enough time outside watching the sky you will see the remnants of an ancient, giant comet ending their existence in a brief flash of light.
For a more in depth technical article about the Taurids --- see here.
* Had to fight an urge to add the word Batman! to this title.