Latest / Kidcast Daily / Ep337: Light Year Explained

Transcript

Ep337: Light Year Explained · Kidcast Daily

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  Spin the wheel, Let's take a ride.
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  Sports and science bursting from inside a world of wonder.
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  Open wide. Come.
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  On. Kids, let's amplify kid cats.
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  Daily starts your day. Fun and laughter come your way.
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  Sports and trivia games galore. Welcome to Kick Ass Daily, where
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  we bring you news, trivia, fun facts, and more made just for
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  curious kids like you. Have you ever looked up at the
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  night sky and wondered how far away those tiny Points of Light
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  really are? Space is very big, and the
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  distances are so large that using kilometers or miles
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  becomes hard to imagine. Scientists use a special unit to
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  make these distances easier to talk about.
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  Today we are exploring the Lightyear, a way to measure
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  gigantic distances in space. Let's start with the one thing
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  we can measure very well, the speed of light.
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  Light moves extremely fast. In a vacuum like outer space,
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  light travels about 299,792 kilometers every second in
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  miles. That is about 186,282 miles per
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  second here on Earth. Light takes a little over one
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  second to go from the moon to us.
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  Light from the sun takes about 8 minutes and 20 seconds to reach
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  Earth. That is why when you watch a
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  sunrise, you are actually seeing light that left the sun several
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  minutes earlier. Here's a yes or no question to
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  get your brain buzzing. Is a light year a measure of
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  distance rather than time? Yes, even though it sounds like
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  it measures time, a light year measures distance.
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  It is the distance that light travels in one year in a vacuum.
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  Scientists use a standard year length of about 365.25 days for
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  this calculation. Now let's define it clearly.
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  One light year is about 9.46 trillion kilometers in miles.
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  That is about 5.88 trillion miles.
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  That number is so big that it is helpful for talking about how
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  far away stars and galaxies are. If you tried to travel one light
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  year by car, even at a steady 100 kilometers per hour without
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  stopping, it would take more than 10 million years.
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  If you could ride a fast jet airplane at about 1000
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  kilometers per hour, it would still take more than 1,000,000
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  years to cover one light year. That shows why scientists prefer
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  to keep using the speed of light as their measuring stick when
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  talking about space. A helpful way to think about a
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  light year is to connect distance and the time that light
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  needs to travel. If a star is 10 light years
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  away, the light you see from it tonight left that *10 years ago.
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  You are not using years to count time on a clock.
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  You are using the time light needs to travel to tell you how
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  far away something is. This lets astronomers describe
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  huge distances with a single number.
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  Did you know that different objects in space are at very
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  different light year distances from us?
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  Some are fairly close and some are incredibly far.
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  Many stars you can see on a clear night are within a few 100
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  light years. The center of our Milky Way
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  Galaxy is about 26,000 light years away.
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  The Andromeda Galaxy, which is the nearest large Galaxy to us,
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  is roughly 2.5 million light years away.
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  That means the light from Andromeda we see tonight started
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  its journey long before humans had telescopes.
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  Here comes a trivia question that adds something new.
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  How many light years away is the closest star to the Sun?
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  Called Proxima Centauri? It is about 4.24 light years
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  away. That is close in space terms,
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  but still far beyond anything we can travel to with today's
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  spacecraft. Now let's talk about how
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  astronomers measure these huge distances for nearby stars.
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  Scientists use a method called parallax.
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  They observe a star from Earth at different times of the year
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  and see a tiny shift in the stars apparent position compared
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  to very distant stars. From that small shift and
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  careful math, they can work out the distance in light years.
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  For farther objects they use other tools like studying how
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  bright certain types of stars are or measuring redshift for
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  very distant galaxies. These methods are tested and
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  compared so that the distances are as accurate as possible.
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  You might wonder if light always moves at exactly the same speed
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  in a vacuum. Yes, but here is a yes or no
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  question with a new detail. Does light travel slower in
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  water than in a vacuum? Yes, light moves slower in
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  materials like water or glass. In water, light travels at about
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  3/4 of its vacuum speed. That is one reason lenses can
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  bend light to help focus images in cameras and telescopes.
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  Let's try a few quick facts you can share.
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  The North Star, called Polaris, is roughly 433 light years away.
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  When you look at Polaris, you are seeing light that began its
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  trip centuries ago. Some bright stars you see in the
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  sky, like Vega, are about 25 light years away.
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  Many stars in the band of the Milky Way you see on a dark
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  night are thousands of light years distant.
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  Here is another trivia question with a new piece of information
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  about how wide is our Milky Way Galaxy from one side to the
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  other. Measured in light years, it is
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  about 100,000 light years across.
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  That means if a beam of light started at one edge and traveled
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  straight across the Galaxy, it would take about 100,000 years
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  to reach the other side. Light years also help explain
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  why we say we are looking back in time when we look far into
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  space. Telescopes that capture light
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  from very distant galaxies are seeing them as they were
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  millions or even billions of years in the past because that
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  is how long the light has been traveling to reach us.
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  This is not a trick. It is a direct result of how
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  fast light moves and how large spaces.
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  Time for one more trivia question to bring in a fresh
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  fact. How long does sunlight take to
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  reach Neptune, the farthest major planet from the sun?
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  On average, about four hours. That number changes a bit
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  because Neptune and Earth move around the Sun, but it is around
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  4 hours for light to make that long trip.
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  Light years are useful not only for stars and galaxies, but also
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  for explaining how fast information can move.
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  Signals that use light, like those in fiber optic cables,
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  move very fast, but even they cannot go faster than light in a
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  vacuum. This speed limit helps
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  scientists understand the timing of events in space, like when a
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  star brightens or when a distant object explodes and releases
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  light across the universe. Astronomers record when that
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  light arrives at Earth, and by comparing observations from
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  different telescopes, they learn where and how far away the event
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  was. Here is a final yes or no
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  question that teaches a new detail.
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  Do astronomers use a slightly longer year of about 365.25 days
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  when calculating a light year to account for leap years?
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  Yes, they use a standard called the Julian year, which averages
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  365.25 days. So the definition is consistent
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  and precise. Let's wrap up with a quick
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  recap. A light year is a unit of
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  distance, not time. It is the distance light travels
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  in one year in a vacuum, about 9.46 trillion kilometers, or
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  5.88 trillion miles. Light is very fast, taking just
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  over a second to reach us from the moon and a little over 8
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  minutes from the sun. The nearest star beyond the sun,
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  Proxima Centauri, is about 4.24 light years away.
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  The Milky Way is about 100,000 light years across, and
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  Andromeda is about 2.5 million light years away.
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  Astronomers measure distances using methods like parallax for
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  nearby stars and other techniques for faraway galaxies.
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  Light moves slower in materials like water than in a vacuum.
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  Using light years helps scientists describe and
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  understand the huge scale of space.
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  Keep asking questions, keep exploring, and the universe will
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  keep offering more to learn. Grab your breakfast, feeling
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  finds adventures waiting. Don't be late, Today's the day
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  we celebrate. Kick Ass Daily starts your day.