Sep. 28th, 2015 04:53 am
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Clear skies, in the UK, for an astronomical event - it can happen!

large photo )

Canon 70D with 70-300 IS zoom lens, ISO 1600, f/5.6, 1/2 s. Taken with 10s delay to let the vibrations from pressing the shutter release die down! I'm pleasantly surprised how many stars are visible.
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io9 has an intriguing story about a planet larger than Earth and as dense as lead. (Not to mention being white hot).

A bit of digging turns up the paper that this story is based on, made available last week. However, in the course of searching for it I found this paper by another team, which whilst referencing the first paper (I assume they saw a draft) uses IR rather than optical measurements to come up with a diameter for 55 Cancri e that is half as much again as that derived in the other paper. That cuts the density dramatically for the same mass (which is fairly well-characterised) thus taking the planet from 'twice as dense as Mercury' to 'about as dense as Mars', which is a little less dramatic.

What both papers make clear, and which the io9 story doesn't, is that even if 55 Cancri e is as dense as lead, it isn't made of lead. Or comparably-dense silver or thorium, or even, alas, iron with a core of platinum. Rather, it's made of iron, but iron compressed to much greater than normal density by the sheer mass of the planet, some eight times that of Earth. Incidentally, a planet that close to its star couldn't be made of lead - at over 2,000 degrees, it would have boiled away...

So, be a little wary of dramatic science claims. It may be that someone has missed another paper, or just picked the one with the more dramatic conclusions.
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The Kepler planet-hunting probe has demonstrated the clarity of its detection system by seeing not only the dip in light as a planet passes in front of its star, and indeed not only the dip again caused by the planet's own light as it passes behind, but the smooth increase in light from the planet as it's orbit takes it through the full range of phases.

This movie explains the light curve.

To me, that we are not only detecting planets a thousand light-years away, but actually measuring their changing phases as they orbit their star, is nothing short of amazing. I can also see some fun school-level science teaching from this, such as using the light curve to estimate the size of both the planet and the star.
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... evidence that this may actually have happened. Observations indicate that what was assumed to be a protoplanetary disc around BD+20 307 could be no such thing, as the star turned out to be both a binary and far too old to be in the early stages of forming a solar system. Rather, the interpretation now is that we're looking at the debris cloud from a relatively recent (within the last half-million years or so) collison between terrestrial-size planets.

Alternatively, someone has been testing out the Death Star.
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Info on Comet Holmes, which brightened a million-fold last week and is now apparently an easily-visible naked-eye object in Perseus.

More info from Heavens-Above

It looks as if what we're seeing is an expanding spherical shell of matter. Debris from a gas eruption? From the H-bomb nudging into a new orbit? Dispersing nanobots? Time will tell...


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Simon Bradshaw

September 2017



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