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No, this is not a reference to The Dark Star, Star Trek enemies or even the Kardashians
You see, almost six years ago Michael Brown, Professor of Planetary Astronomy at the California Institute of Technology, announced that newly found exo-planet Eris was larger than Pluto. Subsequent discussions at the International Astronomers Union resulted in a new definition of a “planet”, ultimately leading to the demotion of Pluto to a Dwarf planet. And then there were eight. I wonder what Mickey and Snow White would say to that?
But new calculations, reported in the New York Science Times article recently concerning the Planet formerly known as Pluto and its interloper Eris, suggest the possibility that this may have been a big mistake. New observations by a Paris Observatory team hinted that, even after accounting for uncertainties, that the largest possible Eris is still smaller than the smallest possible Pluto. Who to believe? Sounds like the green-eyed monster woke up; mine’s bigger than yours.
Over the many years since its discovery in 1930 Pluto’s size has been downsized (I know the feeling!) so many times as increasingly accurate measuring systems have been developed, that led one astro-comic to declare that, after plotting it’s age and subsequent recalculations of mass and distance on a graph, it should actually have disappeared by 1984. Stargazers with a sense of humor, who knew!
Despite their being billions of miles apart they would apparently look exactly the same size in the sky with any differences really only visible, as Dr. Brown stated, by measuring with a “really, really big ruler”. Astrognomes are very precise with their measurements, and how do we know this? Because boys and girls, they work with Standard rulers. A Standard ruler is an astronomical object whose approximate size is known such that by measuring its apparent angular diameter in the sky, one can determine its distance from Earth. Or so they say.
The point being that cosmic distances are quite difficult to determine, especially as they rely successively on ever more complex methodologies. There’s the problem sunshine; not enough rulers. This succession of methods is known as the cosmic distance ladder. Real direct distance measurements to an astronomical object is only possible for those objects that are "close enough" (within about three thousand light years) to Earth.
The ladder analogy arises because no one technique can measure distances at all ranges encountered in astronomy. Each rung of the ladder provides information that can be used to determine the distances at the next higher rung. For example, several methods rely on a Standard Candle, which is an astronomical object that has a known luminosity. Wow, this Astronomy business is really complicated; first we had standard rulers, now we have standard candles. Whatever will they think of next? Standard lamps? An Evening Standard maybe? So, by comparing the known luminosity of a Standard Candle to its observed brightness, the distance to the object can be computed using the inverse square law. Such objects of known brightness are termed standard candles.
Sounds to me that this cosmic laddering leads to massive amounts of distance approximations which are increasingly inaccurate the further away we measure. Why not think of a Very Large Number, add a few zeroes and call it wally. Which just goes to prove that Astronomy is only a slightly more accurate version of Astrology, peering through the mists of time, the cosmic crap, and the galactic garbage to ascertain the truth about who we are, where did we come from, and where are we going. It just used more high tech equipments like candles and rulers, rather than crystal balls.
A significant issue with Standard candles is the recurring question of how standard they are. For example, all observations seem to indicate that type Ia Supernovae, that are of known distance, have the same brightness. But if the properties of Supernovae type Ia are different at large distances then “Houston we have a problem”. This is not just a philosophical issue. For example, in the 1950s, Walter Baade discovered that the nearby Cepheid variables used to calibrate the Standard candle were of a different type than the ones used to measure distances to nearby galaxies. The nearby Cepheid variables were population I stars with much higher metal content than the distant population II stars. As a result, the population II stars were actually much brighter than believed, and this had the effect of doubling the distances to the globular clusters, the nearby galaxies, and the diameter of the Milky Way. Whoops!
And even last year Pieter van Dokkum, a professor of astronomy at Yale Charlie Conroy of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., reported in the journal Nature that the number of stars in the universe had been undercounted, and they now estimate that there could be three times as many stars out there as originally thought. Wow, three times more.
It’s all to do with how you count the dwarf stars that can’t be seen outside of our own Milky Way galaxy, which requires assumptions based upon the color of light being emitted by galaxies. These astronomes found that the proportions of dwarf stars to Sun-like stars in elliptical galaxies was 1,000 or 2,000 to 1, rather than the 100 to 1 in the Milky Way. A typical elliptical galaxy, thought to consist of about 100 billion stars, would therefore have one trillion or more stars. But such galaxies only account for about a third of all galaxies, leading to the new estimate of at least three times as many stars over all.
Like I said earlier, any number estimates that Astronerds come up with can always be improved by adding a few zeroes. Either that or we need some new candles and a more accurate ruler. You can have mine; its twelve inches but I don’t use it as a rule.