00:00Locating the North Star is quite easy on a clear night.
00:04The only thing you need to do is find the Big Dipper.
00:07Those two stars on the end of the Dipper's cup point the way to the North Star.
00:12See?
00:13It's the tip of the handle of the Little Dipper, or the tail of the Little Bear.
00:16It's in the constellation Ursa Minor, over there.
00:20People have been watching the North Star for centuries.
00:24This bright star is also known as Polaris.
00:27It's situated almost directly over our planet's North Pole, which makes it a great landmark
00:32for a traveler without a compass, or a GPS on their smartphone.
00:37It's also Earth's closest Cepheid.
00:40That's what we call a star that pulses regularly in brightness and diameter.
00:44Polaris is also part of a binary system of two stars.
00:48It's got a dimmer sister.
00:50It's known as Polaris B.
00:52You can actually see it circling the North Stars from Earth.
00:57But the more astronomers watch Polaris, the less they understand.
01:01The problem is, no one can agree on how big or distant the star is.
01:06Scientists have several ways to estimate the mass, age, and distance of a star like Polaris.
01:12One method is called the stellar evolution method.
01:16After studying the brightness, color, and rate of pulsation of a star, experts use this
01:21data to figure out how big or bright it is, as well as what stage of life it's in.
01:27Once these details are clear, it's not hard to find out how far a star actually is.
01:33It's simple math once you know the luminosity of a star in real life and how dim it looks
01:37from our planet.
01:40Such models are especially precise for stars like Polaris because the rate of their pulsing
01:44is directly related to their brightness.
01:47This makes it easy to figure out the distance to any of those stars.
01:52Astronomers trust this method so much that Cepheids have become an important tool for
01:56measuring distances all across the universe.
02:00At the same time, there are other ways to study the North Star, and they don't agree
02:04with the stellar evolution models.
02:07Polaris is a so-called astrometric binary.
02:10It means you can see its companion going around it.
02:13It looks as if a circle is being drawn around the bigger star.
02:18To complete one orbit, the smaller star needs around 26 years.
02:23Even though astronomers haven't made detailed observations of Polaris B's full circuit,
02:28they've seen enough to know what its orbit looks like.
02:32Using this information, one can apply Newton's laws of gravity to calculate the masses of
02:36the two stars.
02:37Combined with the Hubble Space Telescope's new measurements, these calculations lead
02:42to very precise numbers.
02:44Polaris is supposed to be around 3.45 times the mass of the Sun, but that's much less
02:50than the mass you get from stellar evolution models.
02:53They suggest a value of almost 7 times the mass of the Sun.
02:58But there's another reason why this star system is weird.
03:01After calculating the ages of the stars, researchers concluded that Polaris B is much older than
03:07its bigger sibling, but it's extremely unusual for a binary system.
03:12Normally, both stars are of the same age.
03:16One explanation might be that at least one of the measurements is simply wrong.
03:20After all, Polaris is a difficult star to study.
03:23Since it's positioned above our planet's north pole, it's outside the field of view of most
03:29telescopes.
03:30As for those telescopes that do have the needed equipment for measuring the star's properties
03:34precisely, they're typically used for studying much more distant and fainter stars.
03:40Polaris is simply too bright for such instruments.
03:43It blinds them.
03:44There's a theory that the main star of the Polaris system was once two stars, but they
03:49collided a few million years ago.
03:52Such a binary collision could rejuvenate stars by pulling in extra material and making the
03:56stars look as if they went through the fountain of youth.
04:00It would also explain some other oddities, since stars that appear as a result of binary
04:05collisions don't fit stellar evolution models.
04:08Unfortunately, so far, none of the theories have been confirmed.
04:13The north star is actually a big deal.
04:16Earth is spinning non-stop, which causes the sun to rise and set and stars to travel across
04:21the sky.
04:23Our planet is also tilted.
04:25That's why we have seasons.
04:27If we drew a line through the axis Earth spins around and extended it over 300 light-years
04:33past the North Pole, at the end of that imaginary line, there would be the north star.
04:38It stays almost exactly at the same spot in the sky at all times, and always points the
04:43way north.
04:44It's really important for navigation.
04:47People heavily relied on it in the days before GPS.
04:50If you were standing on the equator, Polaris would be right at the horizon.
04:55At the North Pole, it would seem to be right over your head.
04:58In other words, using the star's height in the sky, you can not only figure out the needed
05:03direction, but also understand where you are on Earth.
05:07Curiously, there's no south star.
05:10There isn't a bright enough star right above the south pole.
05:13But one day we might get such a star.
05:16When you spin a top on the table, its end moves in a circle.
05:20We know this phenomenon as precession.
05:23Earth behaves in the same way, and the north and south poles won't always point towards
05:27the same spots in the sky.
05:30In the next 26,000 years, it may cause the north star to change from Polaris to a few
05:35other stars and back again.
05:38One day, the title of the north star will go to Vega.
05:41It's the fifth brightest star in the night sky and the second brightest in the northern
05:45celestial hemisphere.
05:47Vega has another name, Alpha Lyrae.
05:51That's because it's the main star of the Lyrae constellation.
05:54Vega has been one of the most crucial stars to people since ancient times.
05:58It's very bright and blue, hence very recognizable.
06:03Vega was the north star several thousand years ago, and it'll regain this status in 12,000
06:08years or so.
06:10This star is located a mere 25 light-years from Earth.
06:13It's just 450 million years old, which makes it way younger than our own 4.6 billion-year-old
06:19star system.
06:21Astronomers study Vega to learn more about star systems in the early stages of their
06:26formation.
06:27Vega is almost directly overhead at mid-northern latitudes on a summer night.
06:32It hides behind the horizon for only seven hours a day.
06:35You can see it on any night of the year.
06:38If you travel farther south, you'll find out that Vega lies below the horizon for longer
06:43periods of time.
06:45But in Alaska, northern Canada, and some parts of Europe, Vega never sets.
06:50Vega's blue-white light is bright enough to be featured a lot in ancient cultures, from
06:55the Chinese, to the Polynesians, to the Hindus.
06:59Vega's name can also be translated as falling or swooping.
07:03This is a reference to the times when people regarded this constellation as a swooping
07:07vulture, not a lyre.
07:10Vega was also the first star to get photographed, other than the sun, of course.
07:15To do it, astronomers at Harvard College Observatory used a 15-inch refractor, and it happened
07:21again in 1850.
07:23Around two decades later, an amateur astronomer broke down Vega's light to reveal various
07:28elements making up the star.
07:30In 2006, thanks to telescopic observations, scientists found out that Vega was whipping
07:36around so fast that its poles were several thousand degrees warmer than its equator.
07:41The star rotates every 12.5 hours and is at 90% of its critical rotation speed.
07:47That's the velocity at which an object can tear itself apart.
07:52In 2013, researchers announced that they had discovered an asteroid belt around Vega.
07:57It means there might be planets somewhere out there among space rocks.
08:02There are two areas, an outer region that contains icy asteroids and an inner region
08:08with warmer space rocks.
08:11Scientists can examine bright stars like Vega using NASA's mission called TESS, which
08:16stands for Transiting Exoplanet Survey Satellite.
08:20It was launched in 2018 to conduct an all-sky survey.
08:24The main goal of this mission is to search for exoplanets, but the satellite can also
08:29look for star variability.
08:32By examining such stars as Vega, TESS can help scientists learn more about the early
08:37stages of star evolution.
08:39That's it for today!
08:41So hey, if you pacified your curiosity, then give the video a like and share it with your
08:45friends!
08:46Or if you want more, just click on these videos and stay on the Bright Side!
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