February 8 – Big Smalls

Today’s factismal: Most stars aren’t visible because they are too small and too cool.

If you go out at night and look up in the sky, you will probably see lots of stars out there. Though a couple of them are bright enough to look like they have color (e.g., Betelgeuse, Aldebaran) most of them just look like little white dots in the black velvet of night. But what you may not realize is that you are just seeing part of the picture. That’s because when you look at the night sky you can only see those stars that are big enough and bright enough to be seen – and they are just a small fraction of the stars out there!

Most stars are much smaller than the Sun (a.k.a., "Sol").

Most stars are much smaller than the Sun (a.k.a., “Sol”).

How small? Well, astronomers aren’t certain but they agree that at least 70% of all stars out there are “dwarf stars” with less than half the mass of the Sun (known as “Sol” in astronomy circles); some think that it may be as much as 85%! These stars range in size from about ten to five hundred times the mass of Jupiter (to an astronomer “size” always means “mass”). Because they are so small, they burn hydrogen very slowly. Eventually, they will run out of hydrogen and turn into white dwarfs, in a mere 500 billion years or so. In the meantime, these small stars, like Epsilon Indi BB, give off very little visible light and most of their “shining” is done in the infrared (“heat”) portion of the spectrum.

The hotter something is, the "blue-er" its color is. This is true of stars as well as planets.

The hotter something is, the “blue-er” its color is. This is true of stars as well as planets.

The rare big stars, like VY Canis Majoris, have a lot of fuel but they burn through it fast becoming super-hot and glowing a bright blue that slowly changes to red as they lose mass and cool off slightly. (And I do mean “slightly”; at its start, a hypergiant like VY Canis Majoris burns about 500,000 times as brightly as the Sun but it gradually drops to a mere 200,000 times before exploding into a nova.)

Bigger stars are much more massive and much hotter; that makes them brighter and bluer than small stars

Bigger stars are much more massive and much hotter; that makes them brighter and bluer than small stars

So there are a lot of small and dim stars that aren’t visible to the naked eye; they are the candle to the rare big star’s searchlight. But the thing is that there are a lot more candles than there are searchlights. For every star you see at night, there are at least 100 more that are too small to be seen.

A look at the Milky Way using ultraviolet and infrared light (Image courtesy NASA)

A look at the Milky Way using ultraviolet and infrared light
(Image courtesy NRAO)

Big big or small, astronomers study them all. And here’s an image of what those stars look like when we peek at them using ultraviolet and infrared light. “Ordinary” stars that we can see at night glow a greenish white, where newborn and small stars heat up the surrounding dust and make it glow a bright violet for infrared and a startling purple for radio waves. If you’d like to see more pictures like this, and maybe help find hot stars in other galaxies, then point your scope to:

February 6 – The Sky’s A Rockin’!

Today’s factismal: Nearly 42,000 meteorites hit the Earth every year.

Odds are, you’ve seen the really cool dashboard video of the meteor that light up the sky in Illinois and Wisconsin last night. Right now, we don’t know much about this particular meteor other than it was big and bright. We don’t know if it landed somewhere on Earth like the 42,000 other meteorites than come to ground each year or if it headed back out into space like the The Great Daylight Fireball of 1972. We’re not even sure where it came from – was it a piece of a comet or a chunk of an asteroid?

The Great Daylight Fireball of 1972 (Image courtesy and copyright James M. Baker)

The Great Daylight Fireball of 1972 (Image courtesy and copyright James M. Baker)

What we do know is that there will be nearly 70 different chunks of rock and ice that speed by the Earth in February alone! They’ll zoom past at distances ranging from just outside the atmosphere to 78 times the distance to the Moon. They range in size from the size of a tiny house (about 36 ft) to the size of a tiny village (about a mile across). These rocks are made up of chunks of comets and asteroids and even bits of Mars and the Moon that have been blasted into space by impacts from other chunks of rock!

A meteor streak across the Milky Way (My camera)

A meteor streak across the Milky Way
(My camera)

What is important about these chunks of rock is that they tell us how dynamic our Solar System is. Instead of being a dead old system with an orbit for everything and everything in its orbit, the Solar System is a dynamic, ever-changing system with the planets and comets and asteroids interacting to change orbits and thrown new stuff in new places. And they can provide us with samples from other planets and from the earliest formation of the system. Besides which, they are just plain pretty!

A meteorite as seen from above the atmosphere  (Image courtesy NASA/Ron Garan)

A meteorite as seen from above the atmosphere
(Image courtesy NASA/Ron Garan)

But the best thing about meteor is that you can help scientists learn more about them! If you download NASA’s Meteor Counter App (available for iPad, iPhone, and iWannaMeteor), then you’ll be able to send NASA scientists valuable information on the number of meteors that hit during the shower. They’ll then use that information to help us understand how likely it is that we’ll get hit. To learn more, go to NASA’s web site:

January 30 – ISIS Is It

Today’s Factismal: The joint USA-Canada ISIS Satellite launched January 30, 1969.

Let’s suppose that you live in Oklahoma and want to talk to a friend who lives in Canada. In the days before the internet, you had four choices: You could travel to Canada to talk to your friend, but that would take weeks and cost a lot of money. You could send your friend a letter, but that would take weeks even if it was fairly inexpensive. You could call your friend on the phone, but that was very expensive even if it was fast. Or you could radio your friend, using the ionosphere to send the signals over the horizon to Canada. And, because it was cheap, fast, and tricky, that’s what geeks would do.

Sending radio signals using the ionosphere

Sending radio signals using the ionosphere

Using the ionosphere to skip signals over the horizon and around the globe has been popular since radio was born. And it was the experience of the early radio “hams” that helped scientists predict the existence of a layer of ionized gas in the atmosphere that they called the ionosphere (“sphere of ions” in science-ese). The gas acted like a mirror, reflecting radio signals over the horizon, just as a periscope reflects light around a corner. And thanks to the ionosphere, ham radio operators and others could send their signals more than 2,000 miles across the globe, instead of being limited to the sixty miles or so that direct line of sight provides. (This is also why you can sometimes receive an AM radio signal from very far away.)

But the ionosphere is more than just a plaything for radio enthusiasts. It is also part of the Earth’s magnetosphere; the magnetic field that protects life on Earth from the deadly ionizing rays of the Sun. Without the ionosphere, solar flares would scorch the Earth and coronal mass ejections would blast the surface with radiation. But thanks in part to the ionosphere, these events get turned into harmless auroral displays; bright bands of fire, dancing in the night sky. And the Sun pushes the ionosphere closer to the Earth on the day side and pulls it further away on the night side, affecting communications and ion distribution. Because it interacts with the Sun, the ionosphere is not a fixed layer with a constant geometry. Instead, it is a constantly-moving, ever-changing layer of churning electrons, protons, and ionized plasma.

The ISIS 1 Satellite (Image courtesy CSA)

The ISIS 1 Satellite (Image courtesy CSA)

There have been a number of satellites that have investigated the ionosphere, either by recording electrical activity from above or by dipping samplers into it. One of the most successful of these was the ISIS 1 satellite. A joint project of NASA and the Canadian Space Agency, ISIS 1 measured the density of electrons in the ionosphere and the relative contributions from the Sun and from cosmic rays. The success of this program led to more joint satellites and eventually to the development of the CANADARM, a remote waldo that is installed on the International Space Station.

If you’d like to experiment with the ionosphere yourself, then join NASA’s INSPIRE (Interactive NASA Space Physics Ionosphere Radio Experiments) Project:

January 25 – Hot Topic, Cool Science

Factismal: IRAS was launched on January 25, 1983.

Astronomy entered a new age in 1983, with the launch of the Infrared Astronomy Satellite, or IRAS for short. IRAS wasn’t the first telescope into space, nor was it the first infrared telescope. But it was the first infrared telescope in space. And that is what matters, because it turns out that space is the place to be if you want to see something that is invisible.

The InfraRed Astronomical Satellite (IRAS) discovered the first exoplanet (Image courtesy NASA)

The InfraRed Astronomical Satellite (IRAS) discovered the first exoplanet (Image courtesy NASA)

You see, the part of the spectrum that we see is just a very, very limited part of a much wider whole. The visible spectrum, which covers the colors from blue through red, says a lot about the world. But the invisible spectrum, which covers colors that are cooler than red (the infrared) and hotter than blue (the ultraviolet), tells us a lot more about the universe. Part of that is simply because most of the universe is very, very cool. And the rest is because the parts that aren’t cool can be very hot indeed.

The hotter something is, the

The hotter something is, the “blue-er” its color is

And it turns out that the temperature is the key to the color. Back in 1900, Planck was able to show that the color of an object was intrinsically related to its color. For example, the Sun is yellow because the part of it that we see is about 5000 K (about 8540 F, or “really, really hot”). We now use that principle in a number of ways, from taking the temperature of a star to taking the temperature of a baby.

But not all colors of light make it through to the ground. To understand this, think of a brick wall. You cannot see through a brick wall because the bricks block the visible light while allowing more energetic gamma rays to pass through. Similarly, our atmosphere blocks a substantial part of the infrared light while letting the more energetic visible light through. And, just as you can see what’s on the other side of a brick wall by walking around it, telescopes can see the infrared colors blocked out by our atmosphere by going above it.

And when they did, what an amazing array of interesting things they saw. While looking at over 500,000 light sources, IRAS discovered the source of the Geminid meteor shower. IRAS discovered six new comets. IRAS saw the dust created by asteroid collisions as a giant cloud surrounding the Solar System. And IRAS saw 75,000 different galaxies with huge numbers of new stars being born. Most importantly, IRAS gave us the first picture of planets forming from a cosmic cloud of dust and gas.

And the hits from IRAS keep coming, even though the satellite quit working nearly thirty years ago. That’s because there are lots and lots of images from IRAS and other space telescopes that need people to look through them. People just like you! If you’d like to try your hand at classifying infrared images, then try the Milk Way Project:

January 16 – Blowin’ In The (Cosmic) Wind

Today’s Factismal: The Stardust mission returned samples from a comet ten years ago today but the science continues!

There are a lot of things we don’t know in science. But there are a lot of things that we know, too. For example, we know that everything in the Solar System, from the Sun to the Earth to the smallest asteroid, all formed from the same cloud of interstellar dust and gas that collapsed some 4.5 billion years ago. But the Sun is very different from the Earth, which is very different from a comet or an asteroid. So while we know where we came from (as one astronomer used to say “We are all stardust”), how we got here is still something of a mystery. Though we have samples of the rocks on Earth, the Moon, Mars, and several asteroids, all of those have been changed by different geologic processes over the past 4.5 billion years. What we really need to understand how our Solar System formed is a sample of the original material.

The Stardust probe (NASA illustration)

The Stardust probe
(NASA illustration)

And that’s why the NASA Stardust mission happened. In 1999, NASA launched a space probe that was designed to do something that had never been done before: to go to a comet, grab samples of the dust, and return it safely to Earth. The probe looked a little like a five and a half foot long shoe box with a surfboard on either side; the two surfboards were solar panels that supplied the energy to run the instruments. Like other space probes, Stardust included a mass spectrometer to identify the composition of dust and gases it encountered and a camera to provide images. But Stardust’s heart (which was located on the front of the probe) was the sample collector.

Comet dust captured by Stardust (Image courtesy NASA)

Comet dust captured by Stardust
(Image courtesy NASA)

In order to collect samples of comet dust without damaging it or heating it up, NASA used aerogel, a material that is 99.8% empty space. Though aerogel had been invented as a bar bet in 1931, it hadn’t found a practical use until the Stardust mission (since NASA popularized the material, it has become very common in some industrial applications). Because aerogel is so light, it would stop the dust grains gradually with a minimum of breakage. And because aerogel is translucent, the tracks made by dust grains could easily be spotted by scientists.

The Wild 2 comet, as seen by Stardust (Image courtesy NASA)

The Wild 2 comet, as seen by Stardust
(Image courtesy NASA)

Both aerogel and the mission were an unqualified success. Stardust visited the asteroid 5535 Annefrank and discovered that it is larger and more interesting than previously thought. Stardust successfully captured dust both from between the planets and from comet Wild 2 and discovered that comets may not be as pure as we thought. And Stardust took the names of more than a million people (including me!) out between the planets.

During it's twelve year mission, Stardust visited an asteroid and two comets (Image courtesy NASA)

During it’s twelve year mission, Stardust visited an asteroid and two comets
(Image courtesy NASA)

Today, the samples from that mission are being analyzed by people just like you. If you’d like to take a stab at identifying dust grains and helping discover how our Solar System started, then fly on over to:

January 9 – Miss Demeter

Today’s Factismal: Ceres was first thought to be a comet.

Most astronomy fans know Ceres by reputation if not by name. It is the largest body in the asteroid belt, that loose pile of rubble that never quite coalesced into a real planet back when the Solar System was being built. It is small enough that you could it would take 78 chunks of rubble the size of Ceres to build one Moon. But what most astronomy fans (and other folks) don’t know about Ceres is that it has caused trouble for astronomers from the day it was found – and continues to cause trouble today!

When Giuseppe Piazzi first observed Ceres in 1801, he called it a comet. But Johan Bode decided that it was in the right place to be the “missing planet” he was looking for between Mars and Jupiter, and so he called it a planet and gave it an astronomical symbol. Unfortunately for Ceres, astronomers soon discovered over a hundred more “missing planets” in the same neighborhood, and they took to calling it a minor planet (astronomers get upset whenever there are more than ten planets; nobody knows why) when they didn’t call it an asteroid (astronomy speak for “tiny little star-like thingamabob”). And then, when yet more Pluto-sized objects were found in the outer Solar System, Ceres was reclassified yet again as a dwarf planet (see the previous note about astronomers and numbers bigger than ten).

An image of Ceres, taken by the Hubble Space Telescope

An image of Ceres, taken by the Hubble Space Telescope

Even its name is a subject for debate. In America, it is known as Ceres, for the Roman goddess of the harvest. But the Greeks have never consented to that name; they prefer to call it Demeter (which causes all kinds of confusion as there is another asteroid known as 1108 Demeter). And the Germans prefer to call it Hera for reasons that are inscrutable to anyone but a German.

Ceres as seen by the DAWN probe (Image courtesy NASA)

Ceres as seen by the DAWN probe
(Image courtesy NASA)

What is not in doubt is that Ceres is large enough to be shaped into a ball by its gravity, and that it has an interior that is divided into an icy outer part, a rocky middle section, and a metallic core (i.e., meets the definition of planet for everyone but the IAU). It is also possible that Ceres has an inner ocean between the outer icy part and the rocky middle; this is exciting because it makes Ceres one of the few places in the Solar System where life as we know it could exist. Ceres’ size and shape tell us that it is a relic of the early days of the Solar System, when everything was collapsing into small bodies that then collided to form the planets. So we can add planetismal and protoplanet to Ceres’ list of appellations.

The layers of Ceres, as we now know them. We expect to learn a lot more about Ceres once DAWN arrives there in 2015. (Image courtesy NASA)

The layers of Ceres, as we now know them. We expect to learn a lot more about Ceres once DAWN arrives there in 2015. (Image courtesy NASA)

Right now, the DAWN spacecraft is orbiting Ceres. Planetologists (i.e., the folks who still classify Pluto as a planet) are studying the asteroid in order to learn more about how planets form and develop over time, and to see evidence of the early history of the Solar System. They’ll also compare Ceres, which is the largest asteroid, with Vesta, which is the second largest and was visited by DAWN in 2013. As part of the NASA mission, JPL has launched the Asteroid Mappers website, where you can help to identify features on Ceres and Vesta:

December 31 – Hairy Situation

Today’s factismal: The New Year will start with not one but two comets!

There is something special about comets in the sky. These “long haired” wanderers do more than just provide a spectacular light show; they also create meteor showers and change the way we think about the world. And for the next couple of weeks there will be not one but two comets visible in the sky!

The first one is a regular visitor. Called Comet 45P/Honda-Mrkos-Pajdušáková (after the three people who discovered it), it is a member of the “Jupiter family” of comets. These are short-period comets that cycle between rushing by the Sun before heading back out toward Jupiter to cool their heels for a bit. 45P has a period of about five years; the last time it fly by the Sun was in 2011 and the next time will be in 2022.  And it will come relatively near Earth on February 11, 2017 – it will be just about eight million miles away! (If that sounds too close, remember that the Moon is about thirty times closer.) If you can’t wait, go out just before dawn and look to the East with binoculars. That faint, fuzzy patch? That’s the comet. It will get bigger and brighter over the next few weeks so you’ll have plenty of opportunities to see it.

Comet 45P as it flies from Jupiter's orbit in toward the Sun and back (Image courtesy NASA)

Comet 45P as it flies from Jupiter’s orbit in toward the Sun and back
(Image courtesy NASA)

But that’s not the only comet we can see tonight! There is also comet C/2016 U1 NEOWISE which was discovered by NASA’s NEOWISE project. Using images from the WISE space telescope, which spent a year surveying the sky in infrared, the folks at JPL have identified this long-period comet. Instead of just sprinting between Jupiter and the Sun, these comets run all the way from out past Pluto; as a result, their journeys can take tens of thousands of years. Right now, we aren’t sure how long this particular comet takes to complete an orbit or even if it will be ejected from the Solar System. What we do know is that it has already passed its closest approach to Earth and is heading in toward the Sun. As it gets closer, it will get brighter and may be visible to the naked eye early in the morning between now and January 14th when it passes the Sun and heads back out again.

A timelapse photo from SOHO showing what happens to a comet as it goes around the Sun (Image courtesy ESA)

A time lapse photo from SOHO showing what happens to a comet as it goes around the Sun
(Image courtesy ESA)

As comets get closer to the Sun the outermost ice heats up and spews out gasses that form a globe called the coma (which means “hair”). The gasses in the coma then become ionized and get dragged out by the solar wind forming the long glowing tail that is characteristic of comets; this gas tail always points straight away from the Sun. Little flakes of rock dust can also be lost. Because the dust is denser than the gas and isn’t ionized, it can form a second tail that curves away from the comet. (So straight tail=gas, curvy tail=dust. Now go impress your friends.) That dust is left behind in orbits that sometimes lead it to fall on Earth as fireballs.

The surface of a comet as seen by ESA's Rosetta probe (Image courtesy ESA)

The surface of a comet as seen by ESA’s Rosetta probe
(Image courtesy ESA)

And you can see the show using a pair of good, inexpensive binoculars. Binoculars are preferred by new astronomers because they gather a lot of light, which helps you see faint things, and because they give enough magnification, so you can see things like the moons of Jupiter, and because they are inexpensive (about $50). Or, if you’d like to spend about $1,000,000,000 you could launch another Solar and Heliospheric Observatory or SOHO for short.

This satellite, which was launched in 1995 and is still active today, was intended to observe the Sun and tell us more about how solar flares and coronal mass ejections affect life on Earth. But what NASA hadn’t expected when they launched SoHo was that they would see comets. But it turned out that SoHo saw a lot of comets that came to be called “Sun-grazers” for their death-defying feat of diving in near the Sun before heading back out into the dark depths of the outer Solar System.

Sometimes the stress of passing near the Sun or a planet causes a comet to break into pieces (Image courtesy ESA)

Sometimes the stress of passing near the Sun or a planet causes a comet to break into pieces
(Image courtesy ESA)

SoHo is still in orbit today, looking at the Sun and looking for comets. If you’d like to join the folks that have found more than 2,400 comets using SoHo images, then head on over to Sungrazing Comets: