M is for Mars

Yep, you get a bonus post for today to celebrate half-way through A to Z. Let's talk about Mars.

We know more about Mars than any other planet, with the exception of our own homeworld of Earth. We've stared at it through telescopes, sent orbiters and landers, and are even planning manned missions. We are doing everything we can to learn as much as possible about Mars.

What intrigues us so about this little Red Planet? The possibility that humans could live there.

Once we learned how torridly hot Venus was, and how cruel she could be to our vehicles, we kind of lost interest in her and put all our focus to Mars. Don't mistake me, Mars is also contrary when it comes to Earth's metal go-seek-ems. The Mars Curse eats about half of what we send there. Still, we persist because, by gum, we're humans!

Ever since we first peered at Mars through telescopes and saw what might be seasonable variability, we can't help but turn our attention to it. At first we thought the changes might be evidence of a growing season, then we saw canali (channels), which got mis-transliterated to "canals". Imagine our disappointment when the Mariner 9 missions sent us back images of a dry, desolate, pockmarked world. Broke our hearts. We were so hoping it was host to life.

But we haven't given up yet. As we map Mars, we've discovered a vast system of river channels and possible lakes once upon a time, and we've detected water ice in the polar caps.  While the low atmospheric pressure of Mars precludes any liquid water on the surface, we believe water may have flowed there at one time, maybe even oceans (aka the Wet Mars theory). The Viking landers had an astrobiological component, and every lander since has been searching for water, a necessary chemical for life as we know it. It is still possible that extremophile life could be extant on Mars, we just have to know how to find it.

As for human occupation? Living on Mars still captures the human imagination (Mark Watney, anyone?). I know Elon Musk has a plan, there's the Mars One project and  NASA's consideriing a manned Mars mission, though you might have to wait for the next hiring window to open if you're interested in going. (Also astronauts don't make as much money as you'd hope they would.)

Until then, we'll observe it from afar and send more robots.

There's so much we could talk about on Mars, from its volcanoes to its (lack of) magentosphere, to its iron oxide redness to its thin atmosphere to its damp past and more. I favour a Wet Mars theory, though I won't dismiss a White Mars theory.

Hardcore about Mars, because why would you want it any other way:

• Mars, generally  
• Mariner 9 
• Viking missions 
• Curiosity and Opportunity 
• MAVEN 

What do you love most about Mars?
Do you think we can find extant life?
Should humans create a long-term colony on Mars?

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Her Grace is happy to talk about Mars anytime. She's written several post-grad papers about it.

M is for Moon

How can you blog about astronomy and not mention the Moon?

Other than the Sun, the Moon is the most obvious celestial object in the sky. It's mentioned in every human culture since record-keeping began. We've dreamt about it, wrote songs and poetry about it, and eventually got to visit there.

The Moon is the only solar system body humans have visited. If I was an astronaut with an opportunity to walk on the surface of the Moon, I think I'd be most useless, as I'd go all fangirly and rolling in the lunar regolith. Yes, I am a prime candidate for space tourism.

We know lots about the Moon simply due to proximity. We can see it with the naked eye, which makes studying it so much easier.

Facts about the Moon

Distance from Earth: average 384,400 km (or 1.28 lightseconds)
Circumfrence: 10,921 km
Gravity: 1.63 m/s2 (one tenth of Earth's)

Facts are really boring, aren't they?

Cool Facts about the Moon

The Moon it tidally locked to Earth. That means it only shows the one side. The rotation of the Moon matches the revolution of the Moon about the earth. However, due to its elliptical orbit, it does this funny little swinging dance called libration.

The far side of the Moon is often called the dark side of the Moon, not because it's blocked from the Sun. In this case, the word "dark" means "unknown". The far side of the Moon gets its fair share of sunlight, especially during the new moon phase. Until 1959, we had no idea what the far side of the Moon looked like. (It looks like this:)

Note the dearth of maria. Unlike the near side of the Moon,
there's very few cooled lava pools. I find it ironic that the "dark" side of the moon
has a greater albedo than the near side.

Because of the US and USSR's space race to get to the Moon, in the name of peace, an Outer Space Treaty was agreed upon.  Most countries have become party to this treaty. Part of that treaty states that the Moon does not belong to any country, but is free for peaceful exploration and use. (Also: no weapons of mass destruction allowed.)  This treaty is the basis for international space law. (Space, technically, begins above the Kármán line at 100km above sea level.)

What do you love about the Moon, our nearest and dearest space neighbour?

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Her Grace loves the moon when she can stare at it and hates it when she's trying to stare at other stuff. For something with incredibly low albedo, it sure can be a source of nocturnal light pollution.

L is for Lightyear

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."
--Douglas Adams

Space is so big, we measure it in lightyears (ly). Don't let the name fool you. It's not a measurement of time, but distance. A lightyear is the distance light can travel (in a vacuum) in a year (365.25 Earth days).

How far is that? Exactly 9,460,730,472,580,800 meters (or you can round it up to 9.461 x 10¹⁵ meters).  Yep. That's really big. (Why measure it in meters instead of, say, kilometers? Because the meter is a basic unit of Système International. Makes calculation easier and more precise, I promise.)

If that number makes your head spin, sit down, rest awhile and let your brain chemistry reset itself.

Want an easier number to handle?  An astronomical unit (AU) is the distance from the Earth to the Sun. A lightyear is 63,241 AU long.

When it comes to measuring distances, astronomical units tend to be used for stuff within our Solar System, lightyears for the local neighbourhood of stars, and parsecs for everything else. After all, space is really, really big.

A parsec is about 3.26 lightyears. Why the strange number? Because of how we measure faraway stuff.

I'm sure you've played with parallax in high school science, where you hold out your thumb, look at a distant tree with one eye closed, then switch eyes, noting how your thumb appears to move compared to the tree. That's how we measure stuff in space, only we use, the month of June as one eye and the month of Decmeber as the other eye, a nearby star as our thumb and a faraway star as the tree.

Works like this:

A parsec (pc) is the distance that one AU subends an angle of one arcsecond. An arcsecond is 1/3600 of a degree from a circle. As you know, 360 degrees make a circle. (Parsec is an abbreviation of the "parallax of one arcsecond".) If you understood all that, cool. If not, just stick with 3.26 lightyears, as you probably will never need to calculate parallax.

So, how far away from us is stuff?

• Alpha Centauri (nearest known star): 4.6 lightyears (ly)
• Distance to the star Bellatrix (in Orion): 244.6 ly or 75 parsecs (pc)
• Distance from the Earth to the centre of the galaxy: about 26,000 ly or 8 kpc (kiloparsecs)
• Milky Way Galaxy is 100,000 ly or about 30 kpc wide.
• Distance to Andromeda Galaxy (nearest major galaxy): 778,000 parsecs (778 kpc).
• Farthest known galaxy, GN-z11: 13.3 billion lightyears (3,985,819 kpc) 

And that's about as far as we can see. For all we know, there is more stuff out there. We honestly have no idea how big the Universe is.

No hardcore stuff today, unless you want to convert kiloparsecs to meters. I think I've given you enough to keep your head spinning for a while.

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Even Her Grace likes to take a break now and then.

K is for Kelvin, or how we measure temperature in the universe

So yesterday I inflicted math on you and suggested you choose a temperature for a cloud of hydrogen in outer space.  Day before I enforced somewhat easier math on you, but only gave you a temperature in Celsius.

And all the Americans stuck out their lower lips and whined, "But what's that in Fahrenheit?"

Nuh-uh. I am not going to give you any temperature in Fahrenheit, now or ever. Real scientists calculate in Kelvin, as it's one of the base units of Système International. (Degrees Celsius are often used when dealing with relative temperatures and kelvin are used with absolutes.) Astronomers, on the big scale, prefer to measure in Kelvin (K), because we often deal with extremely hot stuff (blue stars at 30,000 kelvin) and extremely cold stuff (hydrogen clouds at 5 kelvin).

What, you say?  Who's this Kelvin dude?

William Thomson, 1st Baron Kelvin was a 19th century scientist who got elevated to the peerage for his marvelous work in thermodynamics. He was quite famous, enjoying the kind of fame and fortune a Kardashian can only dream of. Yep, even Scottish nerds can be meritocratically famous.

He expressed a need for an absolute thermometric scale that went from absolute zero on up. Fahrenheit (imperial) and Celsius (metric) were both based on arbritrary temperatures (like the freezing point of water... but is that pure water or a 50/50 saline solution? and the temperature of the human body, and boiling water... but is that at sea level?).  He wanted a system that was free from such arbitrariness.  The only thing that would be absolute enough for him was the absolute absence of energy, or Absolute Zero.

Thus, the kelvin scale was born and named after Lord Kelvin.

The kelvin scale's good for measuring colour temperature, as there is a correlation between the colour of stars and their temperature.  (Remember a couple of days ago when you calculated your personal peak radiation, and you ended up shining brightly at about 900 nm in the infrared? That's what I'm talking about.)

The human body, at approximately 300 kelvin peaks in the infrared. Our lovely G2-type Sun peaks in the yellow-white visible light range at 5778 kelvin. It's hotter, so that's why it glows so much brighter than we do.

Bellatrix, one of the blue stars in the constellation Orion is a B2-type star glowing at about 22,000 kelvin. But if you go around claiming how hot Bellatrix is, people might wonder if you're interested in Helena Bonham Carter. Bore them with math and science instead.

Wanna go hardcore? Use Planck's law to calculate what temperature you'd have to be to start glowing visible red (about 650 nm).

J is for Jeans Mass and Jeans Length

Essentially, the Universe is a bunch of hydrogen floating about and occasionally clumping together.

You're like, "Dude! No way!" And I'm like, "Way!" And you're all, "Nuh-uh!" And I'm all, "Yuh-huh!" And you go, "But it can't be just hydrogen. There's clumps of stuff!" And Sir Issac Newton goes, "Why's there clumps of stuff? There shouldn't be (but there is! I see clumps of stuff!)" and James Jeans said, "Strewth, there's clumps, because science!"

And he went on to explain how the clumps came to be.

See, our buddy Issac knew just enough about science to question the issues regarding stuff (in this case, hydrogen) clumping together.

So, we've got a whole lotta hydrogen floating about out there in a giant molecular cloud of the stuff. As you know, as soon as a hydrogen atom (or molecule) gets close enough to another one, gravity draws them together.  Get a whole lotta atoms/molecules together, and gravity draws them in. Ah, but here was Newton's quandary: Get enough of them together in a dense enough clump, and the gas pressure would force them away from each other (like how a balloon gets puffy when you fill it). Yet, we've got lots of lumps of stuff. How did that happen?

Our buddy Jimmy figured that if there were clumps, there had to be a reason. He worked out that there was a certain point where, if you got enough atoms togethers, their combined gravity would be stronger than gas pressure, and clumps would happen.

When gravity is equal to or lesser than the gas pressure, nothing happens. When the gravity is stronger, then you get clumps of stuff like stars. The greater the mass of the cloud, the smaller its size, and the colder its temperature, the more unable it will be to resist gravitational collapse. (Temperature? Sure Temperature causes pressure, which is why a boiling kettle whistles while a cold one does not. If your cloud's got a fever, it's gonna need more mass to collapse.)

There was a certain point that this swapover happens. We call that the Jeans Mass (after our buddy Jimmy).

Jeans Length is the radius of a cloud where this collapse will start to happen.

And this is how baby stars are born. As we already know, stars are powered under fusion, which drives nucleosynthesis, and when the stars die and go boom (for various kinds of boom), it scatters all its soot and ash, which then clumps together into rocks and stuff through a process called accretion.

Hey nerd! Go hardcore and do the math:

Jeans Mass:

kB = Boltzmann's constant
T = temperature of the cloud (Kelvin)
r = radius of the cloud
μ = mass of your hydrogen atom
G = gravitational constant
ρ = cloud's mass density (cloud mass divided by cloud volume)

(Wanna cheat?)

Jeans Length:

Same variables as above, with k being the Boltzmann's constant and ρm being the cloud's mass density.

Does math make things easier or harder for you?

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Her Grace does not like math, but she will do it all the same.

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.


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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?

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