Archive | August 2013

Postcard to Saturn: A Big-Hearted Mosaic of Earthlings


Click to enlarge. Trust me, just do it… (Image: NASA/JPL-Caltech)

On July 19, the Cassini spacecraft looked back toward Earth, 898 million miles away, and snapped a photo of us — one of many that went into a remarkable mosaic of the Saturn system assembled by mission scientists.

In that composite image, Earth was a pixel-sized pale blue dot.

On that same day people from more than 40 countries and 30 U.S. states snapped pictures of themselves as they waved back at Cassini and posted them to Twitter, Facebook, Flickr, Instagram, etc. Now, using these images, the Cassini mission has assembled a brand new mosaic — the one above.

If you haven’t already, click on it to enlarge it….

Pretty cool, eh? But wait. Now you really have to go to this link and then click on the image there. Trust me… But please come back here when you’re done.

Even more cool, right? Positively spectacular, I would say.

Now, spread it around so other Earthlings can enjoy it.

Can You See Your Own Brain Waves?


An intriguing new paper in the Journal of Neuroscience introduces a new optical illusion – and, potentially, a new way to see ones own brain activity.

The article is called The Flickering Wheel Illusion: When α Rhythms Make a Static Wheel Flicker by Sokoliuk and VanRullen.


Here’s the illusion:

It’s a simple black and white “wheel” with 32 spokes.

To see the illusion, get the wheel in your peripheral vision. Look around the edge of your screen and maybe a bit beyond – you should find a ‘sweet spot’ at which the center of the wheel starts to ‘flicker’ on and off like a strobe light.

Remarkably, it even works as an afterimage. Find a ‘sweet spot’, stare at that spot for a minute, then look at a blank white wall. You should briefly see a (color-reversed) image of the wheel and it flickers like the real one (I can confirm it works for me).

By itself, this is just a cool illusion. There are lots of those around. What makes it neuroscientifically interesting is that – according to Sokoliuk and VanRullen – that flickering reflects brain alpha waves.

First some background. Alpha (α) waves are rhythmical electrical fields generated in the brain. They cycle with a frequency of about 10 Hz (ten times per second) and are strongest when you have your eyes closed, but are still present whenever you’re awake.

When Hans Berger invented the electroencephalograph (EEG) and hooked it up to the first subjects in 1924, these waves were the first thing he noticed – hence, “alpha”. They’re noticable because they’re both strong and consistent. They’re buzzing through your brain right now.

But this raises a mystery – why don’t we see them?

Alpha waves are generated by rhythmical changes in neuronal activity, mainly centered on the occipital cortex. Occipital activity is what makes us see things. So why don’t we see something roughly 10 times every second?

It’s hard to say what we ‘ought’ to see – perhaps flashing lights, or colors, or patterns – but it is rather interesting that we don’t see (or feel or hear) anything at alpha frequency.

Or do we? Sokoliuk and VanRullen argue that the flickering of the wheel is related in some intimate way to alpha. They offer two lines of evidence here.

Firstly, in a task in which people had to compare the illusionary flicker against a wheel that was actually flickering at different frequencies, the most popular frequency perceived as matching the illusion was 9.1 Hz – i.e. a typical alpha wave one.

But there was a lot of variability:

Secondly, the authors say that perceiving the illusion (not just seeing the physical wheel) causes increased alpha waves:

How could this happen? The authors speculate that there’s a:

Correspondence between the spatial organization of visual cortex (retinotopy, cortical magnification, lateral connections) and the temporal dynamics of neuronal information propagation (neuronal time constants, conduction delays)…

Once alpha activity reaches a critical threshold, the rapid alternation of favorable and less favorable phases for sensory processing produces a “pulsed-inhibition” that can become visible as a regular flicker in the center of the wheel.

This is an extremely cool set of experiments, but to my mind they haven’t yet shown a ‘smoking gun’ which proves that the flicker really is alpha, as opposed to being something that happens to provoke alpha, and be of roughly alpha frequency.

Perhaps a smoking gun would be to show a correlation between an individual’s own alpha frequency (these, we know, differ between people, but are very stable for each individual) and that person’s perceived flicker rate.

Galaxies Collide, Produce Superheated Gas Cloud



Observations with NASA's Chandra X-ray Observatory have revealed a massive cloud of multimillion-degree gas in a galaxy about 60 million light years from Earth. The hot gas cloud is likely caused by a collision between a dwarf galaxy and a much larger galaxy called NGC 1232

Dwarf gets eaten by a spiral galaxy far, far away. X-ray image credit: NASA/CXC/Huntingdon Inst. for X-ray Astronomy/G.Garmire, Optical image credit: ESO/VLT

The enormous swirl in this image is a spiral galaxy that goes by the name of NGC 1232. It appears to be spinning along, minding its own business. But X-ray images allowed astronomer Gordon Garmire to see a strange glow spread across its middle—the purple in the photo above. He knew, then, that something fishy was going on.

Now, in a recently published paper, Garmire proposes that the purple haze is a superheated gas cloud that formed when the spiral galaxy collided with—and consumed—a dwarf galaxy (no longer visible because it’s been eaten by Mr. 1232). If researchers prove that this fireworks display is actually the messy aftermath of a galactic collision, it could shed light on the evolution of galaxies.

Galaxies in Shock

Astronomers are still working out exactly what went down, because this is the first time the aftermath of such a wreck has ever been seen. Garmire suggests that the collision created a shock wave that generated superheated gas with a temperature of 6 million degrees. In addition to the gas, the shock wave may have triggered the formation of massive stars, clustered in a bright spot on the far right side of the image.

Even though the galaxy mash-up is 60 million light years away, NASA’s Chandra telescope was able to capture the X-ray glow of the gas cloud; in the image above that is overlain on a view of the scene in visible light (which appears blue and white). The images were taken in 2008 and 2010, and the analysis was published on this month.

The Collision Continues

Because the composite image only shows two dimensions, researchers aren’t sure if the cloud is flat or spherical. Depending on its form, the cloud’s mass could be anywhere from 40,000 to 1,000,000 times that of our sun.

Although astronomers don’t know when this never-before-seen galactic collision began, the aftermath is expected to last another 50 million years. And if the spiral galaxy did indeed eat its unidentified dwarf neighbor, the researchers say they may be able to analyze the afterglow from this collision and others in the future to figure out how galaxies grow.