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Brian Koberlein
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Do Eeet!

Two years ago I applied to ACEAP as an astronomy educator, and I'm so glad I did.

Want to go to Chile and see some of the most advanced telescopes on the planet? Want to see the southern sky? Want to come back and tell everyone of your astronomy adventures?

Then definitely apply to ACEAP!

If you're not interested, I'd love it if you could share the link with your friends. They'd like to get this out to as many folks as possible.
18 January 2017 Applications Accepted for 2017 Astronomy in Chile Educator Ambassadors Program Applications are now being accepted for the 2017 Astron...
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US citizens or permanent residents only. Or I would apply for sure.
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Many Moons

The most popular model for the Moon's origin is that of a single large impact with a Mars-sized body. But maybe our Moon was formed by multiple impacts over time.

Our Moon is unusually large for a small planet like Earth. Did it form from a single impact with a Mars-sized body, or did it form over time from multiple impacts?
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Elow
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Deep Field Black Holes

At the heart of most galaxies lies a supermassive black hole. How such black holes came to be is a matter of some debate. Did black holes form first, and galaxies later formed around them (bottom up model), or did galaxies form first, and only later did their cores collapse into a black hole (top down model). To answer this question we need to have a good understanding of when these black holes started to form. A new ultra-deep x-ray image is helping to answer these questions.

A deep field image is one that has a clear view of very distant objects. The most famous deep field is the Hubble Ultra Deep Field (HUDF), which showed us just how many galaxies there are in the cosmos. The HUDF was in the visible and infrared, but there are others such as the ALMA Deep Field, which was taken at microwave wavelengths, which gave us a view of distant gas and dust. Now the Chandra X-ray Observatory has taken an x-ray deep field, which gives us a view of distant black holes.

Black holes don’t emit light themselves, but the gas and dust near a black hole can become superheated by the gravitational squeezing of the black hole. Such “active” black holes can emit huge jets of plasma that give off intense x-rays. By studying these x-ray emissions, we can determine things such as the size and rate of growth of the black hole. This new deep field image gathered light from supermassive black holes when the Universe was about 2 billion years old. Since the region observed was the same as the Hubble Deep Field, the team could match x-ray black holes to galaxies in the Hubble deep field, and get an idea of the size and evolution of the black holes and their galaxies. What they found was that the “seeds” for these supermassive black holes were likely on the order of 10,000 to 100,000 times more massive than our Sun. This would tend to support the bottom up model where black holes formed first. If the top down model was correct, we would assume the seeds would be smaller, on the order of 100 t0 1,000 solar masses.

This new data doesn’t completely rule out the top down model, but it is consistent with other evidence that supports the bottom up model. Right now it looks like black holes formed early in the Universe, and this triggered the formation of galaxies around them.

Paper: Fabio Vito, et al. The deepest X-ray view of high-redshift galaxies: constraints on low-rate black-hole accretion. MNRAS 463 (1): 348-374. doi: 10.1093/mnras/stw1998 (2016)

A new x-ray deep field image supports the idea that supermassive black holes formed before galaxies did.
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nice
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Antimatter Astronomy

In astronomy we study distant galaxies by the light they emit. Just as the stars of a galaxy glow bright from the heat of their fusing cores, so too does much of the gas and dust at different wavelengths. The pattern of wavelengths we observe tells us much about a galaxy, because atoms and molecules emit specific patterns of light. Their optical fingerprint tells us the chemical composition of stars and galaxies, among other things. It’s generally thought that distant galaxies are made of matter, just like our own solar system, but recently it’s been demonstrated that anti-hydrogen emits the same type of light as regular hydrogen. In principle, a galaxy of antimatter would emit the same type of light as a similar galaxy of matter, so how do we know that a distant galaxy really is made of matter?

The basic difference between matter and antimatter is charge. Atoms of matter are made of positively charged nuclei surrounded by negatively charged electrons, while antimatter consists of negatively charged nuclei surrounded by positively charged positrons (anti-electrons). In all of our interactions, both in the lab and when we’ve sent probes to other planets, things are made of matter. So we can assume that most of the things we see in the Universe are also made of matter.

However, when we create matter from energy in the lab, it is always produced in pairs. We can, for example, create protons in a particle accelerator, but we also create an equal amount of anti-protons. This is due to a symmetry between matter and antimatter, and it leads to a problem in cosmology. In the early Universe, when the intense energy of the big bang produced matter, did it also produce an equal amount of antimatter? If so, why do we see a Universe that’s dominated by matter? The most common explanation is that there is a subtle difference between matter and antimatter. This difference wouldn’t normally be noticed, but on a cosmic scale it means the big bang produced more matter than antimatter.

But suppose the Universe does have an equal amount of matter and antimatter, but early on the two were clumped into different regions. While our corner of the Universe is dominated by matter, perhaps there are distant galaxies or clusters of galaxies that are dominated by antimatter. Since the spectrum of light from matter and antimatter is the same, a distant antimatter galaxy would look the same to us as if it were made of matter. Since we can’t travel to distant galaxies directly to prove their made of matter, how can we be sure antimatter galaxies don’t exist?

One clue comes from the way matter and antimatter interact. Although both behave much the same on their own, when matter and antimatter collide they can annihilate each other to produce intense gamma rays. Although the vast regions between galaxies are mostly empty, they aren’t complete vacuums. Small amounts of gas and dust drift between galaxies, creating an intergalactic wind. If a galaxy were made of antimatter, any small amounts of matter from the intergalactic wind would annihilate with antimatter on the outer edges of the galaxy and produce gamma rays. If some galaxies were matter and some antimatter, we would expect to see gamma ray emissions in the regions between them. We don’t see that. Not between our Milky Way and other nearby galaxies, and not between more distant galaxies. Since our region of space is dominated by matter, we can reasonably assume that other galaxies are matter as well.

It’s still possible that our visible universe just happens to be matter dominated. There may be other regions beyond the visible universe that are dominated by antimatter, and its simply too far away for us to see. That’s one possible solution to the matter-antimatter cosmology problem. But that would be an odd coincidence given the scale of the visible universe.

So there might be distant antimatter galaxies in the Universe, but we can be confident that the galaxies we do see are made of matter just like us.

Matter and antimatter emit the same spectra of light. So how do we know that distant galaxies aren't made of antimatter?
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Is a black hole antimatter?

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We Three Kings

One of the classic images of the Christmas holiday is that of three wise men or kings traveling to Bethlehem, over which hangs a brilliant star. The Star of Bethlehem has its roots in the opening verses of the Gospel of Matthew, which states:

Now when Jesus was born in Bethlehem of Judaea in the days of Herod the king, behold, there came wise men from the east to Jerusalem, Saying, Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him.

The wise men, or magi in the original Greek, are often represented as kings, but in context were likely astrologers. According to Matthew, they saw some astronomical event as a foretelling of Christ’s birth. There is debate among scholars as to the historical accuracy of event. Matthew is the only gospel that mentions the magi, and many scholars feel it’s a bit of pious allegory to show that the destiny of Jesus was written in the stars. But if we assume for the moment that Matthew’s account is accurate, it raises the question of what exactly the Star of Bethlehem could have been.

Although it’s referred to as a star, it’s clear that’s the one thing it couldn’t have been. On human time scales, stars are fixed and unchanging, and astrology of the time didn’t focus on the stars themselves. Instead it focused on astronomical events, such as the last appearance of a particular star before sunrise, or the conjunctions of stars and planets. One clue is buried in the verse itself, where “in the east” could also be interpreted as “at the rising.” This could be a heliacal rising, where a constellation or planet appears in the sky just before sunrise. For example, the first appearance of Venus as the morning star. Since Venus was long known to astronomers, its heliacal rising would not have been special by itself, but it could have been seen as significant if paired with another bright planet such as Jupiter. One idea proposed by Craig Chester is that it could have been the morning of Venus near the star Regulus (in the constellation of Leo, the lion) followed by a morning conjunction with Jupiter about nine months later. This occurred around 2 BC, but Herod likely died in 4 BC, meaning it didn’t occur “in the days of Herod.”

Another possibility is that the Star of Bethlehem was a comet. Bright comets do appear in the sky from time to time, and have been described as “hanging over” particular cities or lands, as the Star of Bethlehem is often represented. We know that Halley’s comet was visible in the region in 12 BC, and would have been bright enough to be described as a star. But the writers of Matthew would likely have known the difference between a comet and a star, and specifically noted the event as a star. There’s also the fact that comets were generally seen as bad omens, rather than good ones, so it would be unlikely that a comet would mark such an auspicious birth.

A third possibility is that it could have been a nova or supernova. These appear in the sky as “new stars” and are sometimes brighter than even Venus or Jupiter in the night sky. This would match the Biblical description, and might have been interpreted an a good omen. Chinese and Korean astronomers noted the appearance of a nova in 5 BC, which would be around the right time frame, but this nova wasn’t noted by astronomers in other regions, so it likely wasn’t particularly bright. A truly bright nova or supernova, such as the one observed by Tycho Brahe in 1572, would have created a remnant that we could observe today, and there is no known remnant that can be dated to the time of Jesus. It’s possible that there could have been a supernova in the Andromeda galaxy or the Magellanic Clouds, but there is no astronomical record of such an event.

More than anything else, this shows the problems of astrological prophesy. While there isn’t a single event that stands out as a clear origin to the Star of Bethlehem, there are lots of options that “kind of” fit after the fact. This is even true of the Gospel of Matthew itself. Matthew was written around 80 AD, decades after the events it describes, so the astronomical event it mentions would have been interpreted long after the Crucifixion and the rise of Christianity. Even if the author of Matthew felt the Star of Bethlehem was accurate history and not pious fiction, we’ll likely never know the particular event they had in mind.

Paper: Chester, Craig. The Star of Bethlehem. Imprimis. December, 22(12) 1993.

Was the Star of Bethlehem a real astronomical event?
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And we're done here.

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Tis The Season


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The Surface Of The Sun

This image might not look like much, but it’s actually an amazing step forward for solar astronomy. It captures the image of a large sunspot not in visible light, but in microwaves.

The difference is important because different wavelengths of light are emitted by different layers of the Sun’s surface. The visible light we see everyday mostly originates from the photosphere, which is the lowest or deepest part of the Sun that we can directly observe. Microwaves are emitted by the chromosphere, which is the next layer above the photosphere. The chromosphere is much less dense than the photosphere, and has lots of interesting phenomena such as filaments and prominences, formed by a complex dance of thermodynamics, magnetic fields, and plasma. The chromosphere is also unusual because it’s actually hotter than the photosphere. You might expect the Sun is hottest at its interior, and the farther out you go, the cooler things become. That’s true for the photosphere, but not the chromosphere. The chromosphere is coolest near the photosphere with a temperature of about 4,000 K, but heats up as you move outward, reaching a temperature of 25,000 K. Just how the chromosphere gets so hot remains a bit of a mystery.

The mysterious heating of the chromosphere is also what typically allows us to see it. Although it’s very diffuse, parts of it emit visible light. We typically have to look at the edges of the Sun to see it (or during a solar eclipse) since the brilliant light of the photosphere is so bright. But in microwaves the chromosphere is brighter than the photosphere. The problem has always been that microwaves are observed with radio telescopes, which typically have a low resolution. This new image is from the ALMA observatory, which can capture microwave images with a resolution rivaling that of Hubble. These new images have enough detail that we can start to see some of the complex behavior of the chromosphere.

And that may help us understand just how the chromosphere gets so hot.

This sunspot was captured in microwaves, not visible light.
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Ang araw ay sya ang nag bibigay ng liwanag sa buong mundo. 
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Violet Skies

The sky is blue because blue light is scattered more than red. So why isn't the sky violet because violet light is scattered more than blue?

You might know why the sky is blue, but why isn't the sky violet?
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That's right! 
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This Offer Won't Last Long

Total solar eclipses are possible thanks to a chance alignment of the Sun, Earth, and Moon. But this alignment won't last forever.

A solar eclipse is a rare event, and getting more rare all the time. There will come a time when the solar eclipse is only a thing of the past.
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Hu
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Evidence Of Absence

Gamma rays are the most energetic forms of light in the Universe. They’re generated by a variety of sources, from the heated material surrounding supermassive black holes, to the supernova explosions of dying stars. But some have theorized they might also be produced by dark matter.

Dark matter doesn’t interact strongly with regular matter, nor does it interact strongly with light. But since efforts to detect dark matter directly have failed so far, we aren’t entirely sure what makes up dark matter. This has led theorists to develop lots of models about how dark matter might interact with itself. Some dark matter models propose that while dark matter doesn’t interact with regular matter, dark matter particles can collide and annihilate to produce gamma rays, similar to the way matter and antimatter can produce gamma rays through annihilation. Since dark matter is fairly spread out throughout our galaxy, this would produce a diffuse background of gamma rays.

Interestingly, the gamma ray background we observe is diffuse. About 80% of the gamma rays we observe don’t come from a specific source such as supermassive black holes. It’s possible that they come from distant sources we can’t pinpoint, but it could also come from diffuse dark matter interactions. At least that’s been one idea.

But a recent survey of the gamma ray background doesn’t support the dark matter models. Using 81 months of data from the Fermi telescope, the team was able to distinguish the energy levels of different gamma rays, and found that they tend to occur at two energies. The highest energy gamma rays seem to come from known sources such as black holes and supernovae, while lower energy gamma rays don’t have a clear source. However, the distribution and energy range of the lower energy gamma rays is inconsistent with dark matter models, so most of them can be ruled out as the source.

To be clear, this does not mean that dark matter doesn’t exist (as some popular articles have claimed). It does, however, mean that dark matter doesn’t emit gamma rays. So the dark matter enigma continues to evade a solution, and this new study simply adds to the mystery.

Paper: Mattia Fornasa, et al. Angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its dark matter interpretation. Phys. Rev. D 94, 123005 (2016) DOI: 10.1103/PhysRevD.94.123005

Dark matter may exist, but it doesn't emit gamma rays.
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Antimatter Astronomy

Since matter and antimatter emit the same kind of spectra, how do we know distant galaxies are really made of matter?

Matter and antimatter emit the same spectra of light. So how do we know that distant galaxies aren't made of antimatter?
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Sorry for text me back 
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And Proxima Makes Three

If you ask someone to name the closest star, Alpha Centauri is perhaps the most common answer. Some will recognize it as a trick question and correctly answer “the Sun,” but the closest star to our Sun is a faint star known as Proxima Centauri. One of the long-standing questions is whether Proxima is actually part of the Alpha Centauri system, or whether it just happens to be in the same general vicinity. We now have a pretty solid answer.

We’ve known since the late 1600s that Alpha Centauri is a binary pair. The two stars (A & B) are each similar in mass and luminosity to our Sun, and orbit each other every 80 years. Proxima Centauri is much smaller and dimmer, and wasn’t discovered until 1915. By the 1950s we were able to confirm that Proxima wasn’t simply in the same direction as the others (known as an optical double star) but was in the same general region. It also had roughly the same proper motion, meaning that it’s slow drift across the sky is in the same general direction and speed as Alpha Centauri A & B. This meant that odds were good that the three stars are part of a trinary system. But proving this was a different matter.

Although Proxima is in the general region of the other two, it is still about a quarter of a light year away. That’s pretty close for stellar distances, but it’s quite far for an orbiting star. It’s quite possible that Proxima is simply making a close flyby of Alpha Centauri, but doesn’t plan on staying. The key point is whether Proxima has enough speed to escape the gravity of Alpha Centauri, or whether it is gravitationally bound to them. To determine that you need two measurements: radial velocity and proper motion. Radial velocity can be found by looking at the spectrum of a star. As a star moves toward or away from us, its light is redshifted or blueshifted due to the Doppler effect, and we can see this shift in the spectral lines. Getting a precise measure of Proxima’s proper motion is much more difficult because it’s so faint. But recently measurements from the HARPS detector at La Silla Observatory have finally nailed down a precise measure of Proxima’s motion. It’s speed and direction is well under the limit for being gravitationally bound, which means Proxima and Alpha A & B are indeed a trinary system. It’s orbital period is about 550,000 years.

So now we can say the closest stellar system to the Sun includes both Alpha and Proxima Centauri.

Paper: P. Kervella, et al. Proxima’s orbit around Alpha Centauri. arXiv:1611.03495 (2016).
Astronomers have confirmed that Proxima Centauri is part of the Alpha Centauri system
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Y'all retarded, away with this faggottary. -mut
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The Universe is amazing, let me tell you.
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An astrophysicist and physics professor at Rochester Institute of Technology.  Author of "Astrophysics Through Computation" with David Meisel.  Creator of the science outreach project Prove Your World, developing a science television show for children.

If you like my writing, consider supporting me on Patreon.

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