- 2943 - GAIA - measuring the distance to the stars? The Gaia space telescope gauges the distances to stars by measuring their parallax, or apparent shift as they are viewed over the course of a year. Closer stars have a larger parallax as we see them from opposite sides of our orbit around the Sun. Astronomers use this parallax, or shift, to measure the precise distances to the stars. It is simple geometry triangulation.
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----------------- I go into the doctors office
----------------- I explain that I have terrible stomach pains. I know I am passing gas, But, it does not smell or make a sound.
----------------- The doctor wrote out a prescription and an appointment for one week later
----------------- My next appointment was worse. I explained that I still had terrible gas pains and now it smells terrible.
---------------- The doctor shouted , ‘That’s great’.
---------------- “Now that we cleared up your sinuses we will start working on your hearing“.
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------------------------------ 2943 - GAIA - measuring the distance to the stars?
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- The new data comes from the European Space Agency’s Gaia spacecraft, which has spent the past six years stargazing from a perch 1 million miles high. The telescope has to date measured the “parallaxes” of 1,300,000,000 stars .
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- The Gaia parallaxes are by far the most accurate and precise distance determinations ever. Gaia’s new catalogue includes the special stars whose distances serve as yardsticks for measuring all farther cosmological distances.
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- This new data has sharpened the biggest mystery in modern cosmology which is the unexpectedly fast expansion of the universe, known as the “Hubble Constant Rate of Expansion“. How fast is the Universe expanding for every light year of distance away?
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- The universe’s known ingredients and governing equations predict that it should currently be expanding at a rate of 67 kilometers per second per mega parsec. We should see galaxies flying away from us 67 kilometers per second faster for each additional megaparsec of distance they are away from us.
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- In different units this is: 49,300 miles per hour faster for every million light years of distance.
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- Actual measurements consistently overshoot this mark. Galaxies are receding much faster than the calculations say they should. The discrepancy suggests that some unknown quickening agent may exist in the universe. What is this unknown force that is accelerating the acceleration? Some call it “Dark Energy”?
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- It would be incredibly exciting if there were new physics. This Gaia analysis involves reducing possible sources of error in measurements of this cosmic expansion rate. One of the biggest sources of that uncertainty has been the distances to nearby stars, distances that the new parallax data appears to all but nail down.
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- The new data pegs the expansion rate at 73.2 kilometers per second per megaparsec, in line with their previous value, but now with a margin of error of just 1.8%.
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- Launched in December 2013, Gaia has revolutionized our understanding of our cosmic neighborhood. There has been a long history getting here.
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- Copernicus proposed in the 16th century that the Earth revolves around the Sun. At the time, astronomers knew about parallax. If Earth moved, as Copernicus held, then they expected to see nearby stars shifting in the sky as it did so, just as a lamppost appears to shift relative to the background hills as you cross the street. However, the astronomer Tycho Brahe didn’t detect any such stellar parallax and thereby concluded that Earth does not move.
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- Wrong conclusion. He always need more precise measurements. The stars do shift, albeit barely, because they’re so far away. It took until 1838 for a German astronomer named Friedrich Bessel to detect the stellar parallax.
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- By measuring the angular shift of the star system 61 Cygni relative to the surrounding stars, Bessel concluded that it was 10.3 light-years away. His measurement differed from the true value by only 10%.
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- Gaia’s new measurements place the two stars in the system at 11.4030 and 11.4026 light-years away, + or - one or two thousandths of a light-year.
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- The 61 Cygni system is exceptionally close. More typical Milky Way stars shift by mere ten-thousandths of an arcsecond. This is just hundredths of a pixel in a modern telescope camera. Detecting the motion requires specialized, ultra-stable instruments. Gaia was designed for the purpose, but when it switched on, the telescope had an unforeseen problem.
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- The telescope works by looking in two directions at once and tracking the angular differences between stars in its two fields of view, to analyze its new parallax data. Accurate parallax estimates require the angle between the two fields of view to stay fixed.
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- But early in the Gaia mission, scientists discovered that it was not fixed. The telescope flexes slightly as it rotates with respect to the sun, introducing a wobble into its measurements that mimics parallax. This parallax “offset” then depends in complicated ways on objects’ positions, colors and brightness.
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- As data has accrued, and the errors repeated, the Gaia scientists have found ways to separate the fake parallax from the real. Astronomers have managed to remove much of the telescope’s wobble from the newly released parallax data, while also devising a formula that researchers can use to correct the final parallax measurements depending on a star’s position, color and brightness.
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- They have also been able to recalculate the universe’s expansion rate. The way to gauge cosmic expansion is to figure out how far away distant galaxies are and how fast they’re receding from us. The speed measurements are straightforward; distances are hard.
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- The most precise measurements rely on intricate “cosmic distance ladders.” The first rung consists of “standard candle” stars in and around our own galaxy that have well-defined luminosities, and which are close enough to exhibit parallax.
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- This is only sure way to tell how far away things are without traveling there. Astronomers then compare the brightness of these standard candles with that of fainter ones in nearby galaxies to deduce their distances.
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- That’s the second rung of the ladder. Knowing the distances of these galaxies, which are chosen because they contain rare, bright stellar explosions called Type 1a supernovas, allows cosmologists to gauge the relative distances of farther-away galaxies that contain fainter Type 1a supernovas. The ratio of these faraway galaxies’ speeds to their distances gives the cosmic expansion rate.
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- Parallaxes are thus crucial to the whole construction. You change the first step, the parallaxes, then everything that follows changes as well.
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- Gaia’s new parallaxes of 75 different Cepheids, pulsating stars that are their preferred standard candles, to recalibrate their measurement of the cosmic expansion rate.
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- Rival astronomers at the top of the distance ladder game, have argued in recent years that Cepheids foster possible missteps on higher rungs of the ladder. So rather than lean too heavily on them, their team is combining measurements based on multiple kinds of standard-candle stars from the Gaia data set, including Cepheids, RR Lyrae stars, tip-of-the-red-giant-branch stars and so-called carbon stars.
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- Gaia’s new data release is providing astronomers with a secure foundation, The new parallax data and correction formula appear to work well. When used with various methods of plotting and dissecting the measurements, data points representing Cepheids and other special stars fall neatly along straight lines, with very little of the “scatter” that would indicate random error.
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--------------------- Other review available about the Gaia mission:
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- 2932 - GAIA - space telescope measure star’s motion. - The Gaia space telescope has measured the acceleration of the Solar System when it orbits the center of our Milky Way galaxy. The Gaia massive endeavor is to result in three-dimensional mapping of our galaxy, to be completed in 2024.
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- 2097 - Gaia, mapping the stars in the Milky Way. The Gaia spacecraft launched in 2013 has cataloged nearly 1,700,000,000 stars in our Milky Way Galaxy and beyond. Gaia has made a significant contribution to our knowledge of stars in the Milky Way. Yet, it has only mapped 1% of the stars. This alone is information overload. The data set of position and motion is a 3-D map of 1,300,000,000 stars.
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- 2930 - GALAXIES - how many galaxies is the Universe? The universe is an immensely large place. Even distances between the nearest objects are staggering, and the distances across the Milky Way Galaxy and certainly between galaxies in the universe are astonishingly huge to living beings stuck on a planet
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December 20, 2020 GAIA - distance to the stars? 2943
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