How Far Away Is It - 05 - Nearby Stars (4K)

[Music] twinkle twinkle little star I imagine that hundreds of thousands of generations have wondered what they are Here I am again in my backyard looking at the Big Dipper on a clear dark night I can see around a thousand stars for the longest time it was not known whether stars like these shined by their own light or whether they were reflecting the sun's light as all the planets moons comets and asteroids do it's only in the last couple of generations that we have finally reached a point where we know what stars are you'll recall that Copernicus first proposed a sudden centric model for the solar system but you'll note that the outermost celestial sphere did not go away with the Copernican model parallax measurements showed us that the Sun was at the center of our planetary system but no one can find any parallax in the Stars not Tycho Brahe Kepler not Galileo not even Newton the reason it took so long is that stars are so very far away that parallax angles are just too small for the available instruments remember that the moon's parallax was one half of a degree but star parallax is measured in fractions of an arc second in the 1830s there was a race to see who could find a first stellar parallax the astronomer Frederick Bessel won star was 61 Cygni here's how it works if you recall the maximum baseline for parallax measurements for planets was the diameter of the earth for stellar parallax we have the diameter of the Earth's orbit around the Sun that's an increase from around 13,000 kilometers or 8,000 miles to 300 million kilometers or 186 million miles that's 23 thousand times larger so from one side of the Earth's orbit say in July we take a line to the star and map the positions of the more distant stars six months later in January we repeat the process this gives us the angle theta we define stellar parallax as one half this angle this would be the angle at the star with the earth and the Sun making the other two corners of a right triangle the math is the same trigonometry we use for finding distances to the rock in my backyard and to the planets in our solar system of course this is an oversimplification Frederick Bessel mapped 61 Cygni against the distant star background for 28 years observing the stars ellipses that followed the Earth's orbit in 1838 after thousands of measurements and calculations he made scientific headlines by announcing that the parallax of 61 Cygni was 0.314 arcseconds that gives us a distance of 98 trillion kilometers that's 61 trillion miles way too far to be reflecting the sun's light so at this point in the middle of the 19th century we knew that stars burned with their own light if we were to move in a little closer to a star that had a parallax of exactly one second of Arc we'd find it to be 31 trillion kilometers away that's 19 trillion miles this distance is called a parsec it gets its name from the first syllable of parallax and the first syllable of second astronomers like to use it for measuring distances to stars if you're a Star Trek fan you'll hear parsec use a lot in their distance discussions as we discussed in our segment on the solar system light travels at 300,000 km/s or 186,000 miles per second to calculate how far light travels in a year we simply multiply this number by the seconds in a minute the minutes in an hour the hours in a day and the number of days in a year that totals 9.46 one trillion kilometers or 5.8 a trillion miles we call that one Lightyear so one parsec is just over three light-years I'll use light-years throughout this video book but parsecs will come up from time to time let's take a look at some of the stars in our neighborhood out to around 25 light years that's about as far as stellar parallax measurements from ground-based telescopes can take us Proxima Centauri is a dim red star it is the nearest known star to the Sun and thought to be a third member of the Alpha Centauri system it's average luminosity is very low and it is quite small compared to other stars at only about one-eighth the mass of the Sun astronomers predict that this star will remain for another four trillion years a thousand times longer than our Sun Alpha Centauri a and B form a close binary system that is separated on average by a distance slightly greater than the distance between Uranus and the Sun a the main star is bright and yellowish B is not quite as bright and has an orange tinge here's a recent photograph of the Alpha Centauri binary system taken by Hubble turns out that half of all stars are actually binary systems like this one and it is the orbital motion of these kinds of stars that enabled us to measure stellar mass just like we calculated the mass of the Sun by the motion of the planets around it these stars orbit the system's center of gravity called the barycenter we can observe the distance between the stars and locate the barycenter as the center of their elliptical motion we can also observe the length of time it takes to make a full orbit its period this along with Kepler's laws and Newton's gravitational equations is all we need careful observations of Alpha Centauri show that the distance between the two stars is just under 24 times the distance from the earth to the Sun with a z' distance to the barycenter being a little less than half of that in addition we see that the orbital period is almost 80 years this gives us the mass of a AD just over the mass of the Sun and the mass of B that just under the mass of the Sun for the most part the position of stars is virtually identical from century to century but a very small number of relatively nearby stars show dramatic motion across the sky this is called proper motion this magnitude can be measured using the number of degrees moved and the distance to the star you motion towards us or away from us this called radial motion we define it as positive if the star is moving away and negative if it is moving closer for nearby stars this motion can be detected by using parallax techniques with these two numbers the total star motion with respect to the Sun can be calculated using the Pythagorean theorem for example here's Barnard's star it's a dim red star with significant proper and radial motion it's moving so fast that it's called a runaway star here's a look at Bernards star photographed in 1985 it's parallax measurement indicates that its distance was five point nine eight light-years in this second photograph taken twenty years later in 2005 we see that the star has moved 200 arc seconds across the sky that's ten seconds of arc across the sky each year this is its proper motion its new distance is five point nine four light-years which gives us its radial motion combined we get the full motion of the star with respect to the Sun it moved 19 point 1 billion kilometers each year that's eleven point nine billion miles so you can see why it's called a runaway star in fact barnard star is approaching us so rapidly that around eleven thousand seven hundred AD it will be 3.8 light-years from the Sun and that would make it the closest star to our own getting back to nearby stars here's Wolf 359 it is another dim red star in fact it's one of the least luminous stars known Star Trek fans might recognize Wolf 359 as the scene of a great battle between the Federation and the Borg melanda 2-1 185 is another dim red star recent analysis indicates that it may also be accompanied by at least two orbiting planets one was confirmed in 2017 the search for planets around other stars called exoplanets is a major focus these days and research is ongoing this Hubble image shows a white sirius a the brightest star in our nighttime sky along with its faint white tiny stellar companion Sirius me the two stars revolve around each other every 50 years here we have our first parallax star 61 Cygni again modern measurements placed the start eleven point three six light-years away so Bessel's calculation of ten point four light-years was pretty close 61 Cygni is another claim to fame in that it was first noted to have high proper motion as early as 1792 when it got the nickname flying star to add further to this uniqueness in 1830 61 Cygni was determined to be a binary star system with two orange stars [Music] Altair is a bright white star a recent study revealed that Altair is not spherical but is flattened at the poles due to a high rate of rotation Vega is a bright white star and one of the most luminous stars in the sun's neighborhood it has been extensively studied it was the first star to be photographed by astronomers in 1850 it was the North Pole star around 12,000 BC and will be so again around 13,000 700 AD this image of Fomalhaut surrounded by a ring of debris was taken by Hubble the white dot in the centre of the image marks the stars location it's a bright white star but the region around it is black because astronomers use the advanced camera capabilities to block out the star's bright glare so that a dim planet called former halt B could be seen the small white box at the lower right pinpoints the planet's location these observations offer insights into our solar system's formative years when the planets played a game of demolition derby so far we've identified Wolf 359 as one of the least luminous stars in our neighborhood and Vega as one of the most luminous but we haven't been explicit as to what we mean by a luminous stars have a wide range of apparent brightness as measured here on earth the variation in apparent star brightness is caused by two things one stars have different intrinsic luminosity and two stars are located at different distances from us an intrinsically faint nearby star can appear to be just as bright to us on earth as an intrinsically luminous star further away luminosity is what we use to put precise measurements on the idea of brightness it measures the total amount of electromagnetic energy emitted by a star in watts just like a light bulb apparent brightness is measured in watts per square meter because light from stars spreads out over the surface area of a sphere we can use the inverse square law to categorize luminosity for all the stars that have parallax distance information take the Sun for example the apparent luminosity the Sun is measured in my backyard is 1,400 watts per square meter if my backyard solar cells were 100% efficient that's how much electricity each panel would create unfortunately current technology is only 15 percent efficient so I'm only getting around 200 watts per panel plugging our distance to the Sun into the inverse square law we calculate its total luminosity here you can see that the answer is a very big number using Einstein's famous the equals mc-squared for energy equals mass times the speed of light squared we calculate that the Sun is fusing 600 million tons of hydrogen into helium every second and in the process converting four million tons of matter into energy every second to put this into perspective this number is equivalent to around four billion hydrogen bombs exploding every second astronomers use a more complex set of classifications for calculating brightness called magnitudes and absolute magnitudes at 10 parsecs but for our purposes we'll stick with luminosity getting back to stars here's Pollux a bright orange star in 2006 that was confirmed to have an orbiting planet Arcturus is an even brighter orange star in fact it is the fourth most luminous star in the sun's neighborhood capella has a rich yellow color and is the third brightest star in the northern hemisphere after Arcturus and Vega closer examination finds that capella is actually four stars organized as two binary systems caster is actually three sets of binary systems with some bright yellow and some dim red stars since 1838 many astronomers have spent decades measuring star parallax's but the work is so painstaking that up until 1989 only a few hundred were measured that's out of a total population of over 1500 stars within 60 light-years from us in 1989 however the European Space Agency launched a spacecraft called Hipparchus it was specially designed to accurately measure parallaxes without all the interference from the Earth's atmosphere it did so for over a hundred and eighteen thousand stars Hipparchus is accurate to within five to ten percent for stars within 650 lightyears so let's take a look at a few of these [Music] HD one eight nine seven three three is another binary system but the primary star being a dim orange star and the secondary star being a dim red star as we zoom into the star you can see the dumbbell planetary nebula will cover these objects in the next section Hubble has made the first detection ever of an organic molecule in the atmosphere of a jupiter-sized planet orbiting this star the molecule is methane under the right circumstances methane can play a key role in prebiotic chemistry the chemical reactions consider necessary to form life as we know it Aldebaran is a very bright red star it may have a brown dwarf companion a brown dwarf is a star that did not have enough mass to trigger fusion so it only produces light via conventional means this makes it very hard to see Mizar is a bright white star it is famous for being the first binary star system discovered Galileo studied it extensively these two stars take thousands of years to revolve around each other so they were not seen to be rotating around each other in those days it wasn't until the early 1800s that binary stars rotating around each other were seen this turned out to be the first real evidence that gravitational influences existed outside of our solar system once the mass of enough binary stars were calculated it became possible to plot mass versus luminosity on a graph here's what they found instead of having any combination of mass and luminosity we see the stars fall on a line from low mass low luminosity to high mass high luminosity but it is not linear each time the mass is doubled the luminosity goes up 11 times this relationship seems to work for most stars that aren't too massive note that this is an empirical relationship we don't start with an equation and plot its graph we observe events to create the graph and then find an equation that would have created a graph that looks like the one or fits the one we observed now back to stars again spica is a blue star and the 15th brightest star in the nighttime sky it's a close binary system whose components orbit each other every four days Myra is a very high proper motion red star that is shedding an enormous tail of material the tail stretches a startling 13 light-years across the sky it has released enough material over the past thirty thousand years to seed at least three thousand earth sized planets Polaris is our current de North Star for it lies less than one degree from the North celestial Pole it is a double star system with one being a supergiant the supergiant is a classic sofyan variable star sophia's are a critically important kind of star for our distance ladder I'll talk more about them in a minute when we come to Delta CV the first zviad star completely analyzed Antares is a bright red star the sixteenth brightest star in the nighttime sky the size of Antares has been calculated using its parallax and angular diameter his radius is 822 times larger than our Suns launched in 2013 Gaia is a European Space Agency mission to create a three-dimensional map of our galaxy this map shows the density of stars observed by Gaia in each portion of the sky brighter regions indicate denser concentrations of stars while darker regions correspond to patches of sky where fewer stars are observed color representation is obtained by combining the total amount of light with the amount of blue and red light as of April 26th 2018 Gaia has pinned down the brightness and position on the sky of 1.7 billion stars it is also catalogued the parallax proper motion and color for 1.3 billion stars and has relatively accurate distance information on 96 million stars Hipparchus recorded parallax information for a hundred and eighteen thousand stars Gaia has done thousands of times more with all this new data astronomers will be recalibrating the parallax rung on our distance ladder for years to come this view shows both brightness and color information of the 96 million stars selected from the Gaia catalog with the most accurate distance determinations this shows the way the stars will move across the sky during the next 800,000 years now let's take a look at a few stars too far away for Hipparchus well within the range of Gaia Betelgeuse is a very rich reddish cool supergiant star it is also one of the largest and most luminous stars known if it were at the center of the solar system its surface would extend past the orbit of Jupiter C HC yg is a symbiotic star system in which a white dwarf feeds from the solar wind of a companion red and giant star Rigel is the sixth brightest star in the sky since 1943 the star has served as one of the stable anchor points by which other stars are classified [Music] we have now visited a number of stars from our local neighborhood we started with the nearest stars we're parallax measurements from earthbound telescopes were good enough we then moved out to the furthest reaches of the neighborhood using Hipparchus based parallax measurements and we went even further with Gaia in our segment on the solar system we extended the direct measurement and triangulation to include parallax for the planets this segment covered how we measured stellar distance mass luminosity and motion all based on parallax techniques just like we did with the solar system and thanks to the Hipparchus and Gaia satellites we know the parallax for hundreds of thousands of stars which are relatively close to the Sun so we can add stars to the reach of the parallax rung on our cosmic distance ladder but if all we had was parallax we know very little about our galaxy and virtually nothing about the universe beyond but the only thing we get from a star is its light

Channel: David Butler

Views: 257,989

Rating: 4.8420405 out of 5

Keywords: STEM, Stars, howfarawayisit, how far away is it, david butler, stars, parallax, cygni, centauri, proper motion, Wolf 359, 21185, Sirius, vega, altair, fomalhaut, luminodity, distance, parsec, lightyear, star mass, barnards star, pollux, arturus, capella, castor, hipparcos, gaia, aldebaran, mizar, spica, polaris, antares, betelgeuse, rigel

Id: rBfFW6A0aLo

Length: 27min 21sec (1641 seconds)

Published: Wed May 09 2018

Reddit Comments

[u/dangerousbob]

i read that as David Bowie and was oddly confused for a second.