I is for Infrared

Ever since humans first sprouted eyes, we knew light was a thing. We could even discern different colours. For thousands of years, we thought that was it and didn't put any thought that there might be light beyond what the human eye could see. Human skin is also sensitive to heat. When the Sun shines on your skin, you feel warmth.

Then in 1800 polymath* William Herschel discovered what he called "calorific rays". (His original paper announcing this.) While he was observing light through a prism, (which, as you know Bob, splits into its spectrum of a rainbow,) he noticed that the area just beyond red felt warm. He realised that heat was a form of invisible light.

Yep, he discovered infrared (IR), the first noted non-visible part of the the electromagentic spectrum.

The reason our eyes can't see infrared is because the wavelengths are too long for our photoreceptors to pick up. But we can sense it as heat.

Unfortunately, heavy densities of molecules (like humans and atmospheres) are very good and absorbing and emitting infrared, so the best IR telescopes are those in orbit around Earth (like the Herschel Space Observatory). Because infrared is so close to visible light, many of the same technologies that allow us to view visible light can be used to capture infrared--mirrors, lenses and digital detectors. Convenient.

Once you get up and away from the heat of Earth, Infrared becomes a really useful wavelength for astronomers, as it can pass through dust clouds that otherwise block visible light. Also, infrared loves interacting with molecules, which is why we can perceive it as heat. This interaction allows us to use infrared to detect non-star bodies in orbit around our Sun, and possibly in our local stellar neighbourhood.

A Zooniverse project called "Backyard Worlds: Planet 9" allows citizen scientists (like me) to analyse infrared data from NASA's WISE telescope to look for objects like red dwarf stars, brown dwarfs and mysterious planets so far out we might not have recognised them until now. Since these objects don't glow brightly like stars, their peak radiation is more likely to be in the infrared.

This jam's really easy, so if you are interested, please feel free to join in our fun at Backyard Worlds. This project's only been going on for a month or so, and already people have found previously undiscovered stuff.

Here's what the Milky Way looks like from different wavelengths. Compare the infrareds to the (optical) visible spectrum. See how we can see through all the dust?

Do you ever think about what you would look like from a different wavelength?

Heat and hardcore: calculate out at what wavelength you shine,  assuming your body temperature is 36.6 degrees Celcius. So, where in the Electromagnetic Spectrum do you fall?

*A polymath is someone who is a master of many fields. William Herschel, as well as being a well-regarded gentleman scientist was also a spectacular composer.


_________________________________
Her Grace also identifies as a polymath for similar reasons.

H is for Hydrogen and Helium

H is for Hydrogen and Helium, pretty much most of the matter of the universe.

For an astronomer, the Periodic Table of the elements goes like this: hydrogen,  helium, everything else.  (Okay, it really goes, hydrogen, helium, 'metal', starkiller (iron), supernova poop.)

Hydrogen is the most abundant element in the Universe at a whopping 74% of all baryonic matter. Helium takes up about 24%, which leaves about 2% for everything else. Most of that hydrogen and helium float about as Interstellar Medium (ISM), gas clouds like nebulae and gravitationally collapsed into stars.

Why's this? Because in the early seconds of the Big Bang, hydrogen was the easiest atom to synthesis through Big Bang nucleosynthesis. Helium wasn't too hard to synthesise either. Heavier elements tend to be nucleosynthesised in stars through fusion or by supernovae. (This is why they tend to be called "metals" by astronomers, regardless of what they are. If you're not hydrogen or helium, you're a metal.)

A hydrogen atom: one proton, one electron.
Doesn't get any more basic than that. 

How do we know there's so much hydrogen out there? Because hydrogen has its own little radio broadcast channel along the 21cm wavelength line or 1,420 MHz. (Okay, it's more in the range of microwaves, than actual radio waves, but still cool to a radio astronomer.)

In fact, once we were able to identify hydrogen, we were able to see so much more of the Universe, as microwaves at that 21cm frequency can easily penetrate the clouds of dust that tend to block visible light. It was by mapping the hydrogen of the Milky Way that led us to discover it was a spiral galaxy.

Hydrogen hardcore: observing the universe through 21cm.

Do you think we'll run out of hydrogen eventually? How?

____________________________
Her Grace once used hydrogen to fill up party balloons because she'd run out of helium.

(Bonus) G is for Gravity and all things falling "down".

You get a bonus post today because how can you talk about things astronomical without talking about gravity?

Gravity is one of the four known fundamental interactions* (the other three being electromagnetism, strong nuclear force and weak nuclear force) that causes things with mass and/or energy to come together. Since mass and energy are interchangeable (as in E=MC^2) they are both affected by gravity. Time is also affected by gravity.  (Also, the more mass there is together, the stronger the gravity, and the more affect on time it has.)

So, pretend for now the universe is a great big empty nothingness containing only two atoms of hydrogen as far apart as they could possibly be. Because they have mass, they will be attracted to each other, regardless of distance. This attraction is gravity. The closer together they get, the stronger the gravitational attraction.

Now, imagine a universe full of hydrogen. No matter how spread out it is, every hydrogen atom is going to gravitationally interact with every other hydrogen atom. They closer they are, the greater the attraction.

In the early days of the Universe (for those who subscribe to the Big Bang theory), it was full of mostly hydrogen. For whatever reason, certain atoms of hydrogen got attracted to certain other atoms of hydrogen and they all came together. If you get enough hydrogen (a Jeans mass' worth) in a close enough area (a Jeans length's worth), then gravity will collapse it down enough for fusion to start and a star is born. Come back on J-day and we'll talk more about this.

Gravity is what makes fluffy clouds of hydrogen collapse down into stars. If it wasn't for gravity, nothing would bother interacting.

Remember about ten years ago when Mike Brown (aka @plutokiller) suggested the demotion of Pluto to the status of dwarf planet? Much of the current definition of a planet all involve gravity.

1. In orbit around the Sun?  Requires gravitational attraction between the planet and the Sun. Planet has enough velocity so it doesn't fall into the Sun, yet insufficient velocity to escape the Sun's gravity well. (Check out the inverse-square law.)
2. Round in shape? Again, sufficient mass to have enough gravity to overcome mechanical structure and assume a round shape. Astronomers call this hydrostatic equilibrium.
3. Clear the neighbourhood around its orbit?  As a planet takes it yearly trip around the Sun, it gravitationally affects stuff around it, either flinging it out of the way or dragging it in and either acquiring more small moons or new surface craters.  (This is where they claim Pluto and Ceres fall down, because they're kept company by a whole bunch of other rocks in their orbits.)

So yeah. We know what gravity does. It's effect on all things (baryonic and dark matter) is quite noticeable.  However, we don't know exactly what gravity is.  How is it transmitted? How does it communicate? How do those two hydrogen atoms in our hypothesised empty universe know to be attracted to one another? We've been able to detect gravitational waves in our quest to figure out what this is. Does gravity travel via gravitons, the way light travels by photons? Or is there something else we have yet to discover?

No hardcore stuff for you today, as I think I've included sufficient linkage to fry your brain if you so choose

*Einstein says gravity isn't a "force" per se, but rather a consequence of the curve of spacetime and the uneven distribution of mass and energy. Don't worry too much about that, as you can see the results of two masses experiencing gravitational attraction every time you fall down.

Gravity in our everyday life: friend or foe? You tell me.

______________________
Her Grace is wondering if she should be including mathematics in some of her posts.

G is for Galaxy

A galaxy is a hyuuuge collection of stars (and dust and clouds of hydrogen and rocks of varying sizes and dark matter) held together by gravitational force.

The galaxy everyone should know best is our Milky Way galaxy. Look up into the sky pretty much on any clear night and you should be able to see a milky band of fuzzy light stretching north-ish to south-ish. It'll look something like this:

You can see fuzzy light from stars too far away to resolve individually, you'll see dark dust clouds obscuring the middle and do you see those two fuzzy patches to the left?  Those are the Magellanic Clouds. They were named "clouds" by pre-techological humans, even though they're galaxies in their own right, busy tagging along with the Milky Way.

The word 'galaxy' comes from the name Milky Way in Greek: galaxias (γαλαξίας). Rumour has it a goddess was breastfeeding and the milk from her breasts sprayed across the heavens.

Aside from the Milky Way and the Magellanic Clouds, there is one other galaxy that you can see with the naked eye, the  Andromeda Galaxy (M31). Its picture is often used as the poster child for most galaxies:

Granted, it's so far away you can only see the core with the naked eye, but it can be seen here (M31 is the catalogue name for the Andromeda Galaxy) in the Andromeda constellation, just north of the Great Square of Pegasus:

But if it was luminous enough for the whole thing to be seen with the naked eye, it'd actually look this big:

Yeah. That's awesome.

Galaxies come in several shapes: barred spirals (like our Milky Way), spirals (like Andromeda), ellipticals (big egg-shaped clouds), irregulars (like the Magellanic Clouds) and lenticulars (which look like Mexican sombreros).

We're currently riding along in an outside spiral arm of the Milky Way. If you look up at the constellation Orion, you're looking through the spiral arm out into Outer Space. If, six months later, you stare at the constellation Sagittarius, you're looking inward to the center of the galaxy.

There's a supermassive black hole in the middle of our galaxy called Sagittarius A* (A-star). It's a bit hard to see with the naked eye, so you'll just have to rely on those scientists who have access to X-ray observatories and other ways of piercing the thick dust clouds of the galactic core.  Here's how we know there's a black hole in the middle of our galaxy--by its gravitational influence on surrounding stars.

Wanna go hardcore over the galactic core? See what Sgr A* is up to.

What's your favourite galaxy?  Got any pics?

__________________________
Her Grace, as a child, was once very disappointed that she couldn't see the Andromeda Galaxy due to a bad spate of light pollution. Alas, this is still an issue for her.

F is for Fusion, or Why Stars Shine

It wasn't until the 20th Century that we figured out how the Sun burned. Before that, several guesses involved burning oil or some other combustible. But as we learned to estimate the mass of the Sun, it became obvious that previous ideas were incorrect. There simply wasn't enough mass to keep the Sun burning for more than a few thousand years by that method.

Then a scientist called Arthur Eddington suggested that nuclear fusion might be the source of the Sun's apparently long-lived brightness.

Fusion is when two atomic nuclei join close enough to become one atomic nuclei. A surprising amount of energy is released when this happens. TL;DR - this energy is what makes a star shine.

Nerd stuff:
The Sun fuses hydrogen into helium, thus releasing vast quantities of energy in the form of gamma rays.

In smaller stars like our Sun, the fusing of hydrogen into helium takes place through a proton-proton chain reaction. Looks a little bit like this:

In bigger stars, they have fun fusing hydrogen into helium through a Carbon-Nitrogen-Oxygen cycle. It looks more like this:

Wanna have some fun? Look up stellar nucleosynthesis, which explains the output of fusion, and find out what nucleosynthesis makes.

What happens when a star starts fusing Mg into Fe?

______________________________

Her Grace wonders if alchemists knew about fusion, if they'd still try to find methods of turning lead into gold?

E is for Extremophile

Astrobiology is a genuine field of science that studies how life could happen in the universe. While Earth is teeming with biology, it is unfair to compare the rest of the Solar System with our prolific-ness. Could life, in some form, exist elsewhere in the Solar System? If so, and knowing what conditions are there, what form would that life take? Enter extremeophiles, those hardy little unicelluar organisms that absolutely insist on dwelling in places we never thought life was possible.

It's all about figuring out what kind of organisms can survive what kinds of conditions. Looking to known extremophiles on Earth, we've got little critters living in boiling hot springs in Yellowstone, thriving in the saltiest lakes in Utah and cheerfully metabolising away in Antartica. If they can live under such extreme conditions here on Earth, why not elsewhere?

Life on Mars?  Still possible in microbial form. While the radiation-scorched surface where water can't exist in liquid form may appear quite inhospitable, the potential for liquid water below the surface still exists. Life as we know it needs water. We know water ice exists on Mars and water vapour has been detected. Extremophile organisms could dwell underground, or even in the polar ice caps.

And Mars might not be the only place in our Solar System that could host microbial life. Jupiter's moon Europe and Saturn's moons Titan and Enceladus have conditions that might be favourable to extremophiles.

Hardcore: Astrobiology and Extremophiles

Where do you think the most likely place to find extremophile life is on Mars? What kind of extremophile?

________________________
Her Grace has spent a wee bit of time in the field of astrobiology, probably the best use of those Cell Bio classes she took her Freshman and Sophomore years at university.

D is for Dark Matter

Dark matter is not stuff. It is not composed of baryons, or atoms as we know them.

What is it? We're not sure. We can't see it or touch it. (IOW, it doesn't interact with the EM spectrum.) Yet we know it's there.

How? By its gravitational influence on baryonic matter and light.

It was discovered when scientists (such as Lord Kelvin and Fritz Zwicky) tried to work out how gravity affected stuff around it. What they could see and what gravity told them was out there, were two different things. Over and over, they worked the calculations and came up with gravity telling them there was more out there than first thought.

But what could it be?  Until we figure it out, we've called it dark matter. There's a few guesses using ideas involving acronyms such as MACHO and RAMBO and WIMP.

Now, some hypotheses suggest that our understanding of gravity might not be fully correct. That's a possibility. But until we can come up with a better one, we'll take the one we've got and try to account for the strangeness.

Dark matter comes in cold, warm and hot, (references to its velocity, not it's actual temperature). After all, if we could detect its temperature, it would be interacting with the Electromagnetic Spectrum and would therefore not be Dark Matter. There's also Dark Energy, which is believed to drive the expansion of the universe.

So, make any sense?  Don't worry if it doesn't. But if your brain hasn't fried yet, consider this little possibility: could there be some sort of connection between dark matter and Fermi's paradox?

Go hardcore: see how Dark Matter affects the universe as we know it.

Ever wonder if there was something out there that we simply couldn't see?

_________________________________
Her Grace refuses to lose sleep over something she can't see.