Archives For Fun

Solid, liquid, gas. The three states of matter are something I first explored in primary school and water was the best example. You can easily see water frozen in your freezer, and it spews as a gas from your kettle. But if you mess with these normal states, you can do some fun and strange things with something as everyday as water.

We’re all taught in school that water boils at 100°C and freezes at 0°C. This range was defined by a Swedish astronomer(!) called Anders Celsius when he devised the temperature scale that bears his name and which is also known as ‘centigrade’. It’s a very useful way of thinking about temperature[1].

Rather awesomely, there is a way to cool water below 0°C without it becoming ice. The process is called ‘supercooling‘. To try it you’ll need a bucket, some bottled water, lots of salt (we used 700g of the stuff doing this), and a big bag of ice.

Supercooling Kit

Supercooling involves lowering the temperature of a substance but preventing it taking a solid form. In the case of water you can supercool it way down (to about -45°C if you have the right kit) – just so long as you can stop ice crystals forming. Ice forms around ‘nucleation sites’ – places where ice crystals can get a foothold and start growing. These sites are usually impurities in the water or on the surface of some other material that its in contact with. So if you can get very pure water in a very smooth container, you can take it below freezing but keep it liquid. For that reason you should use plastic bottles of mineral water, but filtered water will work too. We used both here.

Salty Slush


  1. Put some water into a bucket and pour all the salt in. Mix it up really well, and try and make sure the salt is all dissolved.
  2. Stand the bottles of water in the bucket and pour in the ice cubes until they almost cover them. You want to cover the bottles just enough that you can still pick them up and also turn them.
  3. Mix it up! Salt reduces the freezing point of water and so the ice will melt quite a bit as this goes along. You want to create a bucket of briney slush. This will let the temperature get very low.
  4. Now you need to leave your bottles alone. Every ten minutes or so, go and rotate them gently. This is just to make sure the water cools down evenly and is cooled throughout. After about 45 minutes the process should be complete. You should be able to feel that the bucket is very cold to the touch – ice will be starting to form on the outside.
  5. Now you can play with your supercooled water…

Supercooling Water

Playing with Supercooled Water

Here comes the fun part! Note that if this stuff isn’t working for you then you probably need more salt and ice – or to give it more time to cool down.

Supercooled water is just waiting to turn into ice. If you gently pick up one of the bottles and then violently shake it, it will almost instantly turn into ice. Shaking it creates air bubbles in the bottle on which ice crystals can form. Once a few have started, it’s a runaway process since the best place for ice crystals to form is on other ice crystals. This is pretty amazing and I couldn’t get a good video or photo of this happening – it was too quick.

What we did a lot of was make ice towers! It’s a seemingly magical process that my four-year-old thought was brilliant. To do this you simply take an ice cube and pour supercooled water onto it. (It’s best to place this on something to contain the excess water!). As the water touches the ice it quickly crystallises and starts to create a tower, building upward as you pour. It’s pretty cool (ahem!). Again: the best place for ice crystals to form is on other ice crystals.

The towers were quite beautiful too, made of pure, transparent crystals. They were quite solid for a minute or two and then quicky disintegrated (it was 22°C in our house).

Why Salt?

Salt is used to grit roads in the Winter because it lowers the freezing point if water and makes the ice melt. In the process it actually lowers the temperature further. If you have a thermometer handy then you can watch the water in the bucket drop in temperature as this experiment progresses. This is why this method works to supercool the bottles – the temperature quickly dropped to around -8°C in our bucket and the slushy mixture makes good contact with the outside of the bottles for quick cooling of the water inside. I suppose this might work in the freezer but opening the lid our of chest freezer would disrupt the cooling and frankly the slushy brine is half the fun!

Science at Home

My four-year-old loved doing this. We talked about molecules slowing down and ice forming. We talked about the Winter and frozen puddles, road gritters, and cold drinks. Mixing in the salt and ice is fun and making ice towers blew her away. The 45-minute wait was the hardest part for her – so we made glowing jelly at the same time!

I’m not sure if supercooling is necessarily something that young kids will take away from this but there’s lots to understand about ice and freezing. The ice towers were very exciting and next time I do this I’ll have some gloves ready for the kids so they can do the pouring and shaking – the bottles are too cold otherwise.

I’ll leave you with another ice tower video:


[1] I cannot fathom why anybody prefers Fahrenheit, which starts with frozen brine at 0°F, the freezing point of water at 32°F and it places the boiling point of water 180° higher at 212°F. Because those are all such handy numbers. Human ‘blood-heat’ was supposed to be at 100°F but things got rearranged – so now it seems odd. Sheesh.

How to Make Glowing Jelly

September 7, 2013 — 28 Comments

Here’s a really simple and fun experiment to do at home: make glowing jelly (or jello, American friends)! The method is really easy – you’re just making jelly – but you do need some kind of UV light source to see the effects[1].


It’s a very simple idea: you make jelly but use a 1:1 mixture of plain ol’ water and tonic water (e.g. Canada Dry). Tonic water contains quinine which is naturally fluorescent and so the resultant jelly will glow under a UV light. Here’s what I did:

  1. Boil 100ml of water and mix with the jelly so it all dissolves.
  2. Top up with cold water up to 300ml.
  3. Add 300ml of tonic water.
  4. Mix it up really well and put it in the fridge.

Quinine glows a blue-ish colour under UV light so I used green jelly to maximise the effect. I’m assuming that the jelly acts as a kind of filter to the fluorescence, so using red jelly would probably result in a very poor glowing jelly. And nobody wants that. There was no blue jelly in the shop; not much blue food in general, actually.

Fluorescence occurs in some materials when they absorb high-energy light photons and then re-emit that energy as lower-energy photons. In this case, the quinine is absorbing UV photons and re-emitting them as visible light (UV light is higher-energy than optical light).

Glowing Jelly!

The results were pretty much awesome. You can see our glowing green jelly above. It tasted great too. Lime turned out to be a good flavour to accompany the tonic water, which would normally have a bitter taste. The kids gobbled it up – under the glow of the UV lamp.

Glowing Jelly

This project was really quick and easy and the kids loved it! I think there may be glowing jelly – and maybe other glowing foods – at Halloween this year.


[1] You can buy UV torches and lights at Maplin or Amazon. There are likely other places too, of course 🙂

I have given a lot of talks over the past few years and I’ve seen more than I can count. This year I saw one of the worst presentations ever – literally in my life I’m pretty sure I’ve not seen one as bad – and I’ve also seen some of the best. I’m starting to piece together what makes a talk good and bad, and I can generally tell within seconds how it’s going to go.

A key component in the personality of a speaker is their choice of software. I definitely have opinions on the different presentation tools, so here they are. If you don’t want to read 1,500 words about slide decks and speaker tools then you had best stop reading now. Okay, you were warned.

Let’s start with the old favourite: PowerPoint. Like Microsoft Word, PowerPoint is synonymous with what it does. People ‘give a PowerPoint’ and ask for your PowerPoint file when they’re actually asking for your slides. Many people don’t even know there are other tools available. PowerPoint hasn’t improved in years, and as such it’s still possible for people to include flashing lights, window-blind transitions and even sound effects (the greatest of all presentation sins!). I haven’t checked, but I think you can still put a MIDI tune into PowerPoint.

If you see this: run away

If you see this: run away

PowerPoint is perfectly capable of producing beautiful slide decks and lets speakers use presenter display (if the sight of it doesn’t make them think their machine is broken). PowerPoint’s modern templates are attractive but because they are so widely used, one should essentially avoid them, or at least significantly modify them. It remains the most popular way to give a talk, and many people have no choice but to use PowerPoint. Many poor souls are forced to use their company’s ill-fitting slide template with its horrible colour scheme. Is it just me or are all ‘company’ PowerPoint themes odious?

For Mac users there is Keynote: PowerPoint’s more experienced older cousin. Keynote wears sunglasses, smokes roll-ups and was making slides before it was cool; PowerPoint wears a Members Only™ jacket and remembers how nice pastel colours were in the 1990s. Keynote is close enough to PowerPoint that is pretty easy to learn the basics but also has a plethora of advanced features and tools that actually place it in a different category. That’s not to say that every Keynote talk is automatically superior of course, just that in the right hands Keynote can produce far more professional presentations.

Alas, using Keynote does not make you Steve Jobs

Alas, using Keynote does not make you Steve Jobs

Keynote’s major weakness is the dreaded Presentation Laptop. This is the laptop you often have to use, but cannot predict. You are usually only even told about it hours before the talk – sometimes not at all! The Presentation Laptop is usually a Windows Vista machine with PowerPoint 2000 installed and an odd obsession with trying to update Adobe Something to a new version during your talk. Keynote users must then either convert the talk to PowerPoint and risk everything going wrong, or export the talk to PDF and risk requiring your host to conjure someone from IT Support to open Adobe Acrobat for them (after first upgrading Adobe Something of course)[1]. It isn’t Keynote’s fault exactly, but if will insist of using the hipster presentation tool for the hipster laptops, then you sort of have to expect it.

PDF is the third way to give talks in general. Usually the PDF folks have long given up on all the above hassles and happily forsaken slide transitions or presenter display[2]. PDF talks often mean that the speaker either prepared a lot for the talk or that they’ve given this talk before. Either way it’s a good sign more often than not. PDF talks are also favoured by the Linux crowd and so you probably know that they are standards compliant and maybe even Creative Commons licensed.

Now let’s cover some of the less well-known but still tragically-common ways to give talks, and let’s start with my least favourite: Prezi.

Prezi is pretty awful and you know it. No come on, when someone stands up to give a Prezi presentation your heart sinks a little doesn’t it? Mine does. No one actually uses Prezi differently to PowerPoint or Keynote, they all effectively show us slides regardless of Prezi’s infinite-canvas concept. It’s a wasted opportunity that’s normally incompatible with the laptop at the podium and often requires several minutes of tech support.

Even this Prezi logo is simple and easy to understand

Even this Prezi logo is simple and easy to understand

Prezi presentations were going to redefine talks – I know I was excited about it at first – but then reality set in. Creating talks in Prezi is a woeful experience. The software is sluggish and has a steep learning curve and you alway seem to have to update it. Then once you’re into the flow you have to steadily unlearn years of presentation norms if you’re going to actually make it worth using something other than slides.

Prezi talks nearly always hit a tech problem and suffer even more than Keynote when faced with the loathsome Presentation Laptop. If you’re a Prezi convert – and it does appear to be a religious experience – then you may be reading this thinking ‘but he clearly hasn’t tried to use Prezi‘. Rest assured I really have. We’ll just have to agree to disagree, and by that of course I mean agree that I’m right an you’re not writing this.

Google Presentations: 2004 Flashback!

There’s also the rising trend for browser-based presentations. As if browsers aren’t abused enough. Google’s online presentation tool is essentially PowerPoint 97 in a browser. Sound like a bad idea? That’s because it is. It is at least slowly getting better all the time though, and has the advantage of working across a lot of operating systems. I’ve also seen several people roll custom HTML-based slide decks. These are often very attractive, and means you can easily incorporate websites into your talk, but because they are done by developers they’re nearly always version 0.1 and riddled with bugs. If the setting is fairly informal then this can be impressive and charming, but in more professional spaces it can be a curse.

Finally a word about talks without slides of any kind. At least some of you will have read this and been saying to yourselves ‘in my day we did talks with nothing but a blackboard/whiteboard/cave wall and they were some of the best talks I’ve seen‘. Well you may be right (although clearly talks were still bad then too) but images, movies and charts are so often required for talks today that I’m afraid it’s too late. It many cases the images, movies and charts are all that is required but often they are crucial to the topic being discussed. It is usually hugely beneficial to talk to the public about astronomy with the aid of images; it is difficult to give professional financial talks without charts of some sort. In web development, screenshots are often required.

There is absolutely still a place for oratory and I love speakers who can perform in this way. But let’s not pretend that it would be good or everyone to do this. Not everyone is Barack Obama and not everyone has the time (or the speech writers) to become him.

The awful truth is that without PowerPoint, Keynote, Prezi – and the rest – most talks would be even worse; we should grateful for the fact that despite the collective failings of these tools, people still manage to give talks at all.

[1] I once turned up for a talk and was told that using my own laptop would be fine, despite the ominous presence of a ‘presentation’ device. However when my talk arrived there was no VGA port – or indeed any port – available. The laptop was plugged into an odd docking station instead. The IT guy had to go and fetch a cherry picker in order to plug-in a ten-foot VGA cable for me to plug into. Luckily they looked far sillier than I did, and the audience found it funny. Shocking.

[2] Personally I used Keynote but these days try to ensure that any slide deck will look 95% fine as a PDF. This avoids the dreaded Presentation Laptop, and mental anguish in general.

Summer Sights

August 1, 2013 — Leave a comment

Once you have a Meade ETX-90 Telescope aligned and ready to go (no small feat, at times) you can see some pretty cool objects in the Summer sky. Saturn is currently riding high, and the rings are at a lovely angle – but that’s about it for the Solar System as I’m not willing to wake early for Jupiter. There’s also Andromeda (and M32 if it pleases), but for the ETX-90 most extra-galactic sources are too faint. Instead I’ve been systematically observing the star clusters and nebulae of the Milky Way. It’s been fun!

The ETX-90 is equipped with Meade’s Autostar system, which can take you on a tour of the sky once it’s set going. It will tell you that you’re off to M11, and then M22 and maybe M5. If you’re like me and don’t have the Messier and NGC catalogues memorised, this is basically a lucky dip of galactic sources. You might find a perfect globular cluster or a dizzyingly faint star-forming nebulae – it’s down to the whim of the Autostar. It’s a lovely way to spend an hour or two on a warm evening.

I’m not much of an astrophotographer so instead I’ve been starting to use up my SLOOH credits and have been recording the same objects using the ‘online space camera’ that I am seeing through the ETX-90. Above you can see my SLOOH views of Saturn, the Wild Duck Cluster (M11) and the Lagoon Nebula (M8).

SLOOH have an iPad app out that lets you buy access on a per-picture basis. It’s expensive (£1.99/image) and not as much fun as controlling the telescope using their usual online interface. However the iPad app is free and pretty easy to use.

The Wild Duck Cluster is my favourite of these images. I’ve not seen it before the other night and it looks most like what I saw through the telescope. The cluster is a very compact open cluster that contains thousands of stars. It’s about 6,000 light years away, and it always humbles me to be able to see so deep into the Galaxy on a night when the Galaxy itself is so clear in the dark night sky. Lovely.

Smile for the camera… in space! In fact it’s cameras as two spacecraft will be taking images of the Earth tonight – there might still be time to get your hair done. The two spacecraft are Cassini and Messenger and although you’ll not even be a pixel in this image – the concept is quite fun.

This idea was started by Carolyn Porco and the Cassini team. A few years ago they created an amazing mosaic image of the Saturnian system, see below, which featured a tiny, pale blue dot: the Earth. It’s just up- and left-of-centre in the image below.


The image is quite astonishing and so they decided to try to organise a new photo of the Earth by Cassini but to rally the world to pay attention and #waveatsaturn this time. This unique photograph (aren’t all photos unique?) will be taken tonight (July 19th) between 21:27 and 21:47 UTC (see other time zones here).

The only problem is that not all the world will be facing Saturn at this moment – you can only look at half of it at once after all. This is where Messenger steps in. Messenger is in orbit around Mercury and will also image the Earth today and tomorrow. Today’s time slots have passed by tomorrow Messenger will image the Earth at 11:49, 12:38, and 13:41 UTC.

So get ready to pose for the camera. These are the ultimate aerial shots.

[Read more at JPL News]


I thought it would be fun to ask Twitter what space fact they would tell kids aged 7. Today I spoke to a class of young children about the Solar System and managed to get a few of these into my hour.

I rather enjoyed the various responses and thought they might inspire more in turn. So here’s a collection of things astronomers would tell very young children. Feel free to tweet me @orbitingfrog with more!

“You can fit over 1,300 Earth sized things inside Jupiter but over 1,300,000 Earth sized things inside our Sun. Stuff is huge!” – Megan Whewell

“If you drove to the sun it would take 152 years.” – Alistair Gibbs

“That [space is] all a big nothing.” – Erik J Cox

“[There’s] more water on tiny Europa than there is on earth” – Ian in Brighton

Io smells like rotten eggs because of the sulphur volcanoes. Stinkiest place in the Solar System?” – We Are All in the Gutter

“The giant planets have likely moved and Neptune and Uranus might have switched places.” – Meg Schwamb

“Tell them that dwarf planet Ceres was once a planet too & survived the downgrade to asteroid status.” – Richard Drumm

“You could float Saturn in the bath. If you had a Saturn-sized bath.” – Jim O’Donnell and John Hicks

“If the sun is a big beach ball, then the Earth is a small marble about a football field away” – Michael Nielsen

“[There’s] Red helium-neon rain on Jupiter and metallic snow/frost on Venus” – @blobrana

“The rain on [Saturn’s moon] Titan is flammable (but there’s no oxygen there so it never burns).” – James O’Brien

NOTE: I’ll add more as they are Tweeted

Ig Nobel Awards 2012

September 21, 2012 — Leave a comment

Highlights from this years’ Ig Nobel Awards for achievements that first make people laugh and then make them think:

MEDICINE PRIZE: Emmanuel Ben-Soussan and Michel Antonietti for advising doctors who perform colonoscopies how to minimize the chance that their patients will explode.

LITERATURE PRIZE: The US Government General Accountability Office, for issuing a report about reports about reports that recommends the preparation of a report about the report about reports about reports.

PSYCHOLOGY PRIZE: Anita Eerland and Rolf Zwaan for their study “Leaning to the Left Makes the Eiffel Tower Seem Smaller”

Different Rainbows

March 3, 2012 — Leave a comment

Walking trough the park today we were caught by a heavy rain shower that literally came out of the clear blue sky. Whilst dashing through town to our car we spotted a spectacular rainbow. In fact it was a double rainbow, which many people will be familiar with. The lower (primary) bow was interesting though, as it appeared to show fringes of green and pink inside the violet edge.

When I got home I learned that we had seen a Supernumerary Rainbow. Luckily I caught a nice photo of it (the best camera is the one you have on you) which is shown above. I also enhanced the image to show the fringes better, this is shown below.

Your common-or-garden rainbow is created when light from the Sun is reflected around inside raindrops and projected back at you (see image below). You stand with the Sun behind you and the rain ahead of you (or all around you) and if the conditions are right you see the rainbow forming an arc. The arc forms at an angle of approximately 42 degrees from the axis of the Sun’s rays. The rainbow is not a physical entity but an optical effect and so it moves as you do – meaning you cannot find the end of it, let alone a pot of gold.

Supernumerary bows are created because different rays of light are actually deflected within each raindrop slightly differently. Imagining a raindrop that is roughly spherical, as in the image above, rays that are incident near the top are deflected out at slightly different angle than one incident near the middle. The rays have fractionally different path lengths.

When light rays of different path lengths exit raindrops, they interfere and either enhance or cancel out particular colours. In reality there are many rays entering many raindrops over a range of incident angles. Over the whole range of angles the wave pairs alternately reinforce or cancel each other to produce light and dark fringes. Each bright fringe is a supernumerary bow.

If the raindrops in the air are all about the same size then this means this effect becomes pronounced and you can easily see the supernumerary rainbow. Rain showers with lots of different raindrop sizes don’t produce supernumerary bows.

In reading up on this topic I also read about lots of other types of rainbow I’d never thought about, including red rainbows that occur at sunrise or sunset and so lack the blue chart of their spectrum, reflected rainbows and zero order rainbows which aren’t rainbows at all but enhancements of the Sun’s apparent brightness due to a rainbow occurring.

Norway and the Aurora

February 28, 2012 — Leave a comment

I returned last night from a trip to Norway to see the aurora. I posted previously about my stint as a Trip Scholar for the excursion on a Hurtigruten vessel, organised by the Oxford Alumni Office. It was a fantastic trip. As well as the Northern Lights we got to see some incredibly beautiful parts of the world, still frozen in Arctic Winter and just getting ready to begin to melt toward Summer and eventually the Midnight Sun. (You can see my Flickr photos here)

We were travelling on the MS Trollfjord and were out at sea for much of the time. To see the stars and aurora you had to don all your warmest gear and head out onto the deck where the wind chill brought temperatures down to -20°C at times.

On our first night we had a chance viewing of the aurora for about ten minutes, which was great but a bit too brief. Many people didn’t catch them at all and the following day there was some disappointment from those who didn’t even realise they had missed the chance.

One the second day of our trip I had an alert that a coronal mass ejection has left the Sun earlier that day and was heading toward the Earth. It was due to hit the Earth’s magnetic field during our final evening on the boat and thus we had an increased chance of seeing the aurora as we sailed into Tromsø to following day. I reported this alert to the group and explained some of the physics of what was going on. The news totally excited everyone and it lead to a day or so of people asking every question imaginable about the Sun, the Earth and the aurora. It was great fun!

As we came into Tromsø the following night the sky was quiet and often cloudy. The ship’s aurora prediction had remained unchanged at a score of one (out of ten). I had explained that when it comes to predicting aurorae, nothing is very concrete. Even our solar flare from earlier in the trip was no guarantee. The disappointment was obvious, but the determination was enormous. A lot of people simply sat out on the freezing deck from sunset and waited. I waited with them.

At around 7:45pm we pulled into a port north of Tromsø (the ship stopped in many places all the time). The town’s lights made it difficult to see much but someone spotted a faint glimmer and we all lined up to inspect it. It intensified and grew green: the Northern Lights had arrived! Over the course of ten minutes or so it became brighter and structures became apparent. It formed an arc over our heads and soon the bottom of the aurora – the curtain – became clearly defined and vertical striations of green regularly punctuated its shape. Everyone was very excited. As the ship pulled away from the town, it turned and we moved alongside the lights for some time. They change rapidly yet often imperceptibly, and pulse in and out of existence at times.

A little while after heading out of the port it was much darker and the lights were better positioned relative to the lights on the ship. Some cloud was appearing, but the aurora were brighter and at times the deck burst into spontaneous applause. It was quite magical. About 45 minutes after they had appeared, the lights were hidden by cloud. Having been on deck for around two hours it was time to go inside, eat and most of all: defrost.

After toasting the lights, and the trip in general, we decided to chance on more trip outside. This time it didn’t take long for the cloud to move away and as we came into Tromsø we were treated to an even better, brighter display. Swirls and arcs and curtains of green light. At times I could even make out the red top above the greens, meaning that Nitrogen at even higher places in our atmosphere was being excited and glowing. We tried to take many photos but they really don’t do justice to what we could make out with our eyes.

I went onto flickr just now and looked for photos taken around Tromsø on either of the two nights we saw the lights. You can see one at the top of this post, taken by Flickr user nitin-p from Tromsø on the first night we saw the lights. The photo looks very similar to what we saw the first night from the deck. The second photo (below) is more like what we saw on the final night as we drew into Tromsø. Brighter, with more structure. This photo is from Flickr user momentaryawe and was also taken from Tromsø.

There were many people on board with very fancy-looking cameras, tripods and other photography kit. Some were even in our Alumni tour group. I gave my email address to many people who have promised to send their best pictures so I can make a gallery here to share around. It would be great to share some photos that were taken from the ship itself.

I was very happy with my Northern Lights trip, and I think the people in our group seemed to get a lot out of it. Not only did they see the lights, but the solar flare warning, and subsequent aurora, left many of them with a better understanding of how such things can be seen, modelled and understood to further our knowledge about the Sun and our relationship to it. Several people expressed the fact that they had no idea how big and powerful the Sun was before the trip and that seeing the lights after being told what makes them happen, enhanced their experience and made the lights better somehow. I was really pleased with that comment and I’m very happy to have done to trip. I would recommend the Northern Lights to anyone, and will be trying to see them again myself one day.

Awesome figure alert!

February 26, 2012 — Leave a comment

The magnetic fields of the inner Solar System animated for your geomagnetic-storm-predicting needs.