S is for Star

S is for Star, and really, you cannot talk about astronomy without mentioning stars. Impossible.

Anyone who's ever expressed the slightest interest in astronomy does so because of stars.  You look up in the sky, see the stars, and go, "Cool!" Stars are what get us interested in space.

Here's an earworm to annoy you for the rest of the day, "Twinkle Twinkle Little Star" (the astronomically correct version):

Stars are the most obvious part of the universe because they shine so brightly along all the electromagnetic spectrum. I consider them a key component of the cosmos. They are the movers and the shakers. They are responsible for all the "metals" (ie elements heavier than H and He) out there. E V E R Y T H I N G out there that's not Hydrogen/Helium, is because of stars.

As you know, hydrogen makes up a good three-quarters of the universe. When that hydrogen (usually in a nebula) gets enough gravity to collapse together, fusion starts and you get a star.

Vital Stats of Stars

Size

Stars range in weight (measured in solar masses or M_☉) from about approximately 0.2 M_☉  to humongous beasts pushing 150 M_☉. Now, that might not seem like a very big range, seeing that one solar mass (M_☉) equals the weight of our Sun at 1.98855 × 10³⁰ kg. But if you look at the radii of these stars, the smallest is about 20% wider than Jupiter, but the biggest is a whopping 1500 times as wide as our Sun. Frickin' huge.

Here's a size comparison:

Also, the bigger a star, the faster it burns through its hydrogen. Really, really big hypergiants have been known to live for the brief moments of a few million years. Living fast, dying young, they leave a really impressive supernova/hypernova before letting its corpse collapse into a neutron star or even a black hole.

Smaller stars last a lot longer. Our own Sun will live about 10 billion years, whereas some red dwarfs could possibly live for trillions of years.

OGLE-TR-122b is the smallest main sequence star we've discovered so far that's still fusing hydrogen. If it got any smaller, it wouldn't have enough gravity to ignite fusion. Unless you're fusing, you ain't a star.

Colour

Stars range in colour, which also correlates with temperature.

Stars are classified according to colour(temperature), with blue stars being the hottest and red stars being the coolest.

O B A F G K M
The spectra of star types. See how the spectra peak in certain colour ranges? That's why stars appear coloured.

Blue O-type stars tend to be 30-40,000 Kelvin.
Blue-white B-types are 20,000 K,
White A and F stars are about 8-10,000 K
G-type stars, like our yellow Sun, are about 6000 K
Red K and M-type stars can be as cool as 3000 K  (For reference, you are around 310 K).

Look up in the night sky and see if you can tell what colour a star is? While most of them appear "white", compare nearby stars to see if you can detect a faint bluish cast or reddish cast.  Betelgeuse in Orion is distinctively red, as is Antares in Scorpio. Rigel in Orion is rather blue.

Why aren't there any green stars?

Actually, there are. Any "white" star is actually radiating in the green part of the visible (optical) spectrum. Green happens to be right in the middle of the spectrum, so when a star is emitting green, it also emits red and blue. Combine all these together (additive colours), and they look white. Our Sun, a G2-type star is generally classified as Yellow-White. But if white is really green, that makes our Sun a yellow-green star. (Consider how much green light gets reflected by plants on Earth. That light's gotta come from somewhere.)

Birth and Death of a Star

So, a star is born from the gas of a nebula. After it gets over its initial teething phase, it settles into the Main Sequence, happily fusing its hydrogen into helium. It'll spend about 90% of its life like this.

Once it runs out of hydrogen, they move off the main sequence, do a few interesting things (like helium flashes, variable pulsing, puffing up like balloons), then die.

When it comes to the death of stars, the manner of its demise depends on its mass.  For smaller mass stars, like our Sun, it'll inflate into a red giant, then with a gentle poof, shed its outer layers, leaving the cooling cinder of a white dwarf.

But if it's a massive star, especially of the live-fast-die-young category, it starts fusing everything into onion layers of elements until it reaches iron. Once that happens, fusion stop, the pressure keeping the star puffy ceases, the star collapses in on itself, rebounds, and dies most violently B A N G!! in a  spectacular supernova.

Don't let the gentle spread of this light echo fool you. This time-lapse covers a period of four years. The light echo is about six light years across. We're talking some serious velocities here.

The energy released in this explosion is enough to start a new wave of nuclear reactions that fuses iron into the higher elements like gold and uranium and blowing them out into the universe.

Whatever is left over gets fused into neutrons and collapses down into either a neutron star or a black hole in the middle of a brand new nebula.

Meanwhile, the shockwave of a supernova can extend for several parsecs, rolling through any neighbourhood nebular clouds of hydrogen, possibly triggering some of it to collapse into new stars.

And thus, the cycle begins again.

Some people just like looking up in the skies. And that's okay. Do you have any favourite stars?  What make them your favourites?  I'm fond of Betelgeuse and Canopus.

No hardcore stuff today, unless you want to investigate more about V838 Mon which occurred in 2002.

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Her Grace is sometimes content just to stare up at the stars with MK-1 eyeballs.

R is for Radio Waves

Since everything in the Universe is so terribly far away, the only way we can science it is through observation. Fortunately, we have the Electromagnetic Spectrum, which can tell us all sorts of things.

At the high end we have the powerful, ionising wavelengths of X-rays and gamma rays, and at the low end we have the more zen-like non-ionising wavelengths such as microwaves and radio waves. All these different wavelengths interact with baryonic matter in different ways. This difference gives us an advantage in astronomy. For example, Earth's atmosphere will block gamma rays but will allow radio waves through.

This makes radio waves both ideal and infernal for ground-based astronomy.

If you tune your car radio in between the official broadcasting stations and listen to the static, some of static comes from the universe. (Radio static is how they discovered the Cosmic Microwave Background, or the radio wave echo of the Big Bang.) Sounds like this:

The atmosphere isn't uniformly transparent to radio waves, because our atmosphere is a rather complex thing. Some frequencies will shoot straight through, others will bounce around. This bouncing around can cause interference, which you can detect on your car radio as static.

The closer you are to population centres, the stronger the radio will be, because we have radio broadcasters and mobile phone cell towers and all sorts of radio-bright sources.  Also, humidity in the atmosphere can block out radio waves.

So, what's an astronomer to do? The best earth-based radio astronomy sites are those away from civilisation, out where it's dry (low humidity) and "radio-quiet".  Western Australia has a Radio Quiet Zone  in the Murchison (our gratitude to the Wajarri Yamatji people, the traditional owners of this land) for the Square Kilometer Array, a large radio telescope. http://skatelescope.org/

Don't think that radio astronomy is out of reach for the amateur astronomers and citizen scientists. There are plenty of amateur radio astronomy clubs and organisations throughout the world.

But if you don't want to go hardcore and build your own radio telescope, you can still experience radio astronomy. If you tune your radio to the frequency of 1420 MHz (that's 1420 AM), you could listen to the hydrogen of the Universe speak to you. Sounds like this.

Spectral lines from other radio-sensitive stuff are detectable in radio astronomy:

• 1400 - 1427 MHz: 21cm hydrogen line
• 22.01 - 22.5 GHz: Water
• 23.6 - 24.0 GHz: Ammonia
• 36.43 - 36.5 GHz: Hydrogen cyanide and Hydroxil
• 72.77 - 72.91 GHz: Formaldehyde

More about how radio astronomy works.

Here's some pictures of stuff in radio frequencies.

Galaxy M51 (Whirlpool Galaxy) in radio and optical:

The planet Jupiter is also radio-bright:

Galaxy M87 showing off a radio-bright jet from its supermassive black hole:

The Sun in optical, radio and X-ray:

Galaxy M31 (Andromeda Galaxy) in radio and visible. Radio has a way of shining through the dust that would normally block visible light. This is one of the advantages of radio astronomy.

What the Milky Way looks like at 408 MHz:

Radio astronomy, indeed astronomy in all the wavelengths provides astronomers with a different point of view.

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Her Grace once observed the universe through a mate's homemade radio telescope. It looked an awful lot like a silver umbrella attached to a laptop, because it was.

Q is for Quasar

In the middle of the 20th Century, astronomers were astounded to find a very bright radio source--stunningly bright. In fact, they were brighter than anything else previously known  (or since, really).  They called them Quasi-stellar Objects (QSOs).

But what were they? Astronomers captured their spectra and had a look. The spectra looked really odd, until they figured out that they were extremely redshifted. Redshift is a nifty astronomy tool. Here's how it works:

Original spectrum    vs   a redshifted spectrum

See the absorption lines in the rainbow spectrum on the left? This is a normal spectrum where some of the light has been absorbed by an element (say, hydrogen and its Balmer Lines).  When the light that makes this spectrum comes from very far away, the expansion of the universe stretches it out and makes the frequency drop. The result is the spectrum on the right, where the absorption lines move in a red-ward direction. This is redshift. Think Doppler Effect.

The greater the redshift, the farther away an object is. The spectrum sampled from quasars were so redshifted it took us a while to figure out just how redshifted they were.

In other words, these really bright radio sources were really, really far away. That was doubly-amazing because of the Inverse Square Law--intensity reduces with distance.

"Dude!" we cried.  What could possibly create so much energy to be so bright from so far away?

Eventually, we figured out quasars were really, really active distant galaxies and that the extreme energy output came from the accretion disks of the  supermassive black holes in the middle of those galaxies. Those suckers can really put on a shine when actively consuming some poor star.

(Is our own Milky Way a quasar? Currently no, as our Sagittarius A* is a rather quiet supermassive black hole at the moment.) Quasars are believed to be an early universe phenomenon because we observe them as coming from waaay back in time. But that doesn't mean that Sgr A* couldn't become a quasar in the future, given enough to eat.

So we figured out that quasars are:

• really old
• really distant
• really bright

Once we established that, we realised they could be used as a kind of anchor point in mapping of the skies. See, the farther away something is, the less likely it is to apparently move.

Want to know more about quasars?

• Easy tricycle level (with training wheels)
• Mountain bike level (for the average science-curious layman) 
• Hardcore Harley Davidson level:
• First papers on quasars
• Subsequent papers on quasars
• More modern explorations on quasars 

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Her Grace prefers to study objects that are a little bit closer than z=7.085.

Using Singing to Create a Positive Emotional Benefit

We haven't had a TASE (Talk About Something Else) Day in a while. We're overdue.

A friend is teaching a child how to master their emotions. Like all good researchers, she asked her peers for their experiences.  I suggested singing as a quick and immediate method the child could use to get themself out of an emotional rut like frustration or anger.

I've always known singing to be a positive mood-lifter, far more effective than just listening to music. I've taught classes in using singing for optimism, and often teach my regular music students how to use music for their emotional benefit. (A bit of a selfish purpose behind this one as well, for if a child learns to love creating music, they'll be more likely to practice.)

Not everyone is a musician, but I believe everyone is capable of singing. You might be a bad singer and woefully out of tune, but you can still sing, and you will still receive the benefits I list below. Never let anyone tell you you shouldn't sing. I refuse to oppress a singer just because they might not have learned to master their pipes yet.

Anyone who's sung out loud may have noticed the centering effect music has. Really, it works, so here I go hardcore with research to explain how this works.

Singing can alter your mood through:

• Employing deep and focused breathing. To sing, one must first draw breath, then release it in a focused and controlled manner to make sound. This deep breathing can also slow heart rate and neural activity. It also provides re-focus, as the brain must concentrate on producing music. Also, the vibrations of music has an effect on the autonomic nervous system. (Clark & Tamplin 2016)  
• Triggering endorphin release. While merely listening to music can make us feel better, the actual performance, whether playing an instrument or singing, has the greater benefit. It requires the singer to be active and not just passive, as a listener would be. This activity stimulates greater endorphin release. (Dunbar et al 2012)(Kreutz G et al 2004) 
• Using a different part of the brain. This disengages the "stuck" brain and engages fresh thinking, which will be less likely to get stuck in a feedback loop. Singing also engages the same part of the brain that processes emotions. Take that over, and the negative emotions are easier to deal with and get over. (Chanda et al 2013) Also helps with stuttering and emotion-related speech issues, like an inability to explain oneself when upset.
• Familiarity. As our common rituals and favourite things soothe us all, the familiarity of a favourite song can also bring us back to ourselves when we feel out of sorts. (Ibid)

So, how does one get this singing schtick to beat off the black dogs?

• Before you find yourself in an emotional bucket o' crap, choose a positive song or ten to be part of your emotional first-aid kit. I've got several, but one that works really well for me is "Before the Parade Passes By" from the musical "Hello Dolly".  Get in the habit of singing your first-aid kit songs now and then so you can get used to how they feel in your chest.
• When you find yourself down or frustrated or angry, pull out the song that "feels right" for the moment, and start singing, even if you don't feel like it. If you're not really in a place you can sing out loud and can't get to one, humming is also acceptable. But if you can do some proper out-loud singing, the deep breathing will do you much good.
• Do not let whatever harshed your original mellow steal the focus from your song. You're here to beat the grief, not let it beat you.  (3/4 or 4/4 are good beats.)  Singing won't solve your original problem, but it will resettle your brain enough for you to have more spoons with which to cope.

Barbara Streisand singing "Before the Parade Passes By".

I am interested to hear results from anyone who's willing to experiment on this method and report back.

References

Clark IN & Tamplin J (2016) "How Music Can Influence the Body: Perspectives From Current Research" Voices, 16, 2

Dunbar RI, Kaskatis K, MacDonald I, Barra V (2012) "Performance of music elevates pain threshold and positive affect: implications for the evolutionary function of music", Evolutionary Psychology, 10, 4

Kreutz G, Bongard S, Rohrmann S, Hodapp V, Grebe D (2004) "Effects of choir singing or listening on secretory immunoglobulin A, cortisol, and emotional state" Journal of Behavioural Medicine, 27, 6

Chanda ML & Levitiin DJ (2013) "The neurochemistry of music (A meta study)" Trends in Cognitive Science, 17, 4





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Her Grace is a Coloratura Mezzo-Soprano by training, though her voice has gone a little smokier with age.

P is for Planet (It's okay, you can call Pluto a planet if you want)

In ancient times, skywatchers noticed certain stars wandered about, and didn't stay fixed like the rest of them. The ancient Greeks called them  πλανῆται (planētai, "wanderers"), and the name stuck. Indeed, if you observe them for several days or weeks, you can notice them inching along relative to the stars in their apparent proximity.

Essentially, a planet orbits a star. All other descriptions are mere refinement.

In 2006 the International Astronomical Union (IAU) issued an updated definition of what a planet is. This came along because more planets had been discovered on beyond Pluto. Once they realised they'd have dozens, potentially hundreds of new planets, they thought they'd come up with some definitions to help sort or categorise the planets. This definition is based off the gravitational interaction of a planet with its environment:

"A planet is a celestial body that:

1. is in orbit around the Sun, 
2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and 
3. has cleared the neighbourhood around its orbit."

Based on this, we've got four Terrestrial planets (Mercury, Venus, Earth, Mars) and four Gas Giants (Jupiter, Saturn, Uranus, Neptune).

"But what about Pluto?" you cry! "They demoted it! It's no longer a planet!"

Uh, yes but no. Pluto is still a planet. Go ahead and call it one if you want. It's new classification may be "dwarf planet", but that is still a planet.

Shot this pic of Venus a month ago
with my smartphone thru my telescope.

When I was a wee junior astronomer, I always thought Ceres got a bad rap. It was classified as a planet when discovered in 1801 (yep, it was discovered before Neptune).  Everyone thought this was nifty, until lots of gentleman scientists started discovering more and more rocks. "Surely these cannot all be planets," they mused. Once they figured out just how small and numerous these rocks were, they reclassified them as "asteroids" in the 1850's, and poor Ceres got demoted.  Yeah. These things happen when you start looking and finding stuff.

So, when the 2006 definition came along, Ceres got re-promoted and classified as a planet once more, albeit in the "dwarf planet" category. I didn't mind (Okay, I was ecstatic!). But many people who weren't around for the 1850 demotion of Ceres, didn't realise the historical precedence for this sort of card-shuffling of our Solar System.

Just like in the 1850's, the 2006's brought a new definition of a classification, because lots more of whatever it was they were classifying were found.  Kuiper Belt Objects (KBOs) were being discovered all the time, and some of them were large enough they could be classified as planets. Also, planets were being discovered around other stars. Everyone went, "That's so cool!" Astronomers went, "Yeah, but we need to sort our rocks."

So the definition was born.

A dwarf planet's not just about size. The only change between the classification of a dwarf planet and a terrestrial planet is that a dwarf planet hasn't cleared the neighbourhood around its orbit. So, Ceres wanders along in the Asteroid Belt and Pluto and Eris and Sedna and company wander about in the Kuiper Belt.  (Trojans don't count, because they're gravitationally shepherded.)

Our Moon, as shot by Your Truly.

Refinement #1:  If an object meets the above criteria, but doesn't clear it's orbit, it's a dwarf planet.

I notice you didn't ask about the Moon (any of them). Couldn't the 2006 planet definition qualify them as well?

Enter Refinement #2: If an object is in orbit around another object, it's a satellite (aka a moon).

Just thought I'd mention this, as we have moons (like Ganymede) that are bigger than Mercury and Pluto. But, as Ganymede and her sisters are in orbit around Jupiter, our Luna (Moon) is in orbit around Earth, and Titan and his mates are in orbit around Saturn, we're calling them satellites.

So, what about rocks that aren't round and aren't orbiting anything else?  We call them Small Solar System Bodies (SSSBs).  These include asteroids, comets, pebbles and anything else with a gravitational connection to the Sun.

So go outside tonight and look up. Can you spot any planets?

Want to know if that bright light up in the sky is a planet or a star? Easy; stars twinkle. Planets don't. (If the light blinks regularly and is moving, it's a plane. If it grows bright then fades and is moving, it's a satellite. If it flares up really bright, enough that you could see it during the day, and lasts several weeks before fading, it's a supernova. If it's fuzzy and grows a tail, it's a naked-eye comet. If it's sudden, really really bright, and takes up your whole field of vision, it's the flashlight of a police officer who's wondering why you're laying on the ground staring up at the sky.)

So, want to know what planets are currently up?  Why, all of them, if you know where and when to look.

The early evening sky favours us with a glimpse of Mercury in Pisces. Uranus is also close by, but twilight might be too bright at the moment to spot it well. (Give it a go in about six months' time. Under the right conditions, Uranus can be spotted with the naked eye and some skill in very dark skies. But if you've got binoculars or a telescope, I recommend this for better luck.)  Mars isn't too far behind in Aries.

My wee shot of Saturn.

A couple of hours after sunset should give you bright Jupiter in Virgo, rising in the east. While easily the brightest planet in the sky right now, you'll really have a show with binocs or a telescope, because you'll be able to spot the four Galilean moons and maybe even see banding.

You'll have to stay up late, or get up early to see Saturn between Scorpio and Sagittarius. This year and next year is excellent to view Saturn through a telescope, as the rings are pretty much as full on tilted our way as they get.

Neptune is a morning star in Aquarius and Venus is close by, just before dawn.

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Her Grace loves to stare up at the sky, and does so nearly every single night.

O is for Orion

Orion has got to be my favouritest constellation. It's so big and obvious and has so many nifty features that makes it ideal for introducing people to astronomy.

Orion sits right over our equator so it's visible to most of the Earth, making it accessible to pretty much every human. Even if you're at the North Pole or in Antarctica, you will still be able to partially view Orion.

Honestly, I don't know where to begin in sharing the awesomeness of this constellation. I'll touch on a few things, but leave the rest of the exploration of this fabulous constellation to you. Right now Orion will be sitting low in the western sky, just after sunset.

On a planisphere, it looks like this:

In the sky it looks like this:

Best viewing time: January, when it's high in the sky, but not too late at night.

The major stars are called:

• Betelgeuse (obviously red)
• Rigel (obviously blue)
• Bellatrix
• Mintaka
• Alnilam
• Alnitak
• Saiph

The Orionid Meteor Shower in October is thanks to Halley's Comet.

There are lots of nebulae in Orion (known collectively as the Orion Molecular Cloud Complex), but the Orion Nebula can be seen with the naked eye. It forms the sword hanging from Orion's Belt.

The Horsehead Nebula is a dark nebula, like we talked about yesterday. Use your telescope to see this one.

Because Orion comes in upside down in Australia, the belt and sword become an asterism called The Saucepan or The Pot:

Hardcore:  All the cool stuff happening in Orion.

I love Orion. What's your favourite constellation and why?

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Her Grace will also observe Orion in July, when it reappears in the sky in the early-morning before dawn.

N is for Nebula

A nebula (Latin for 'cloud') is a cloud of hydrogen, dust and other stuff in outer space. While the Interstellar Medium (aka the ISM, aka 'the space between stuff') tends to have a density of a few molecules per cubic centimeter, a nebula can be hundred times denser than that. (Still, compare it to the Earth's atomosphere at about 10¹⁹ molecules per cubic centimeter.)

Some nebulae are essentially cold hydrogen clouds. An H I region is a neutral atomic hydrogen cloud and an H II region is a cloud of ionised atomic hydrogen (or a bunch of floating protons. Fun, huh?).

You can also get molecular clouds, which are exactly as they sound--clouds of molecular hydrogen, which are ideal for star formation. (Apply your Jeans mass and Jeans length here.)

There's planetary nebulae, which have nothing to do with planets (blame Herschel). These brightly-glowing nebulae result from an old low-mass red giant star puffing off it's outer layers as it dies. Planetary nebulae are a good way for a star to release the products of its fusion--namely, all the elements they synthesized up to iron.

They glow not because they're still undergoing fusion, but re-emitting the light from stars--including its central star. This is why so many of them look like pretty eyes.

Ring Nebula:

Lemon Slice Nebula:

 Eye of God Nebula:

This one looks like Sauron:

Supernova remnants occur when large stars (more than 8 solar masses) end their lives by going boom, er rather, when they go B O O M!!  Becuase of this, they tend to look a bit more scatter-shot than planetary nebulae.

the famous Crab Nebula:

Puppis A:

Now, we know these nebulae are supernova remnants because for a few of them, humans actually witnessed and recorded the supernova that created them. The Crab Nebula went boom in 1054AD and Tycho's Supernova happened in 1572.

Most nebula are visible because they re-emit or reflect light, but some nebula, like dark nebula, are absorption nebulae with enough dust and density to block out any light. Unlike the light hydrogen clouds, these tend to be metallic or 'dirty', with lots of elements and molecules in them.

We know about them because they often block out light and appear as a dark splotch against a brighter background.

Coalsack Nebula, located in the Southern Cross constellation:

While they might not be as visually interesting as their emittive or reflective cousins, don't give them any side-eye, though. These nebulae are as important as their sisters for star formation.

Speaking of star formation, here's a Hubble picture of the Orion Nebula with several young stars:

In conclusion, nebulae are clouds, often left over from the death of stars, that are capable of birthing new stars.

Hardcore: Nebulae.  Have fun and knock yourself out.

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Her Grace is glad she doesn't have to die and go boom in order to give birth to promising young stars.