Do Stars Move? Tracking Their Movements Across the Sky
Δημοσιεύτηκε στις 9 Μαΐ 2017
The
stars look static in the sky, but are they moving? How fast, and how do
we know? What events can make them move faster, and how can humans make
them move?
Support us at: http://www.patreon.com/universetoday
More stories at: http://www.universetoday.com/
Follow us on Twitter: @universetoday
Like us on Facebook: https://www.facebook.com/universetoday
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Team: Fraser Cain - @fcain / frasercain@gmail.com
Karla Thompson - @karlaii
Chad Weber - weber.chad@gmail.com
Before we get going, I’d just like to say, happy 300th episode of the Guide to Space. Here’s to hundreds more.
The
night sky, is the night sky, is the night sky. The constellations you
learned as a child are the same constellations that you see today.
Ancient people recognized these same constellations. Oh sure, they might
not have had the same name for it, but essentially, we see what they
saw.
But when you see animations of galaxies, especially as they
come together and collide, you see the stars buzzing around like angry
bees. We know that the stars can have motions, and yet, we don’t see
them moving?
How fast are they moving, and will we ever be able to tell?
Stars,
of course, do move. It’s just that the distances are so great that it’s
very difficult to tell. But astronomers have been studying their
position for thousands of years. Tracking the position and movements of
the stars is known as astrometry.
We trace the history of
astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus
first created a catalog of the 850 brightest stars in the sky and their
position. His student Ptolemy followed up with his own observations of
the night sky, creating his important document: the Almagest.
In
the Almagest, Ptolemy laid out his theory for an Earth-centric
Universe, with the Moon, Sun, planets and stars in concentric crystal
spheres that rotated around the planet. He was wrong about the Universe,
of course, but his charts and tables were incredibly accurate,
measuring the brightness and location of more than 1,000 stars.
A
thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi
completed an even more detailed measurement of the sky using an
astrolabe.
One of the most famous astronomers in history was the
Danish Tycho Brahe. He was renowned for his ability to measure the
position of stars, and built incredibly precise instruments for the time
to do the job. He measured the positions of stars to within 15 to 35
arcseconds of accuracy. Just for comparison, a human hair, held 10
meters away is an arcsecond wide.
Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.
In
1807, Friedrich Bessel was the first astronomer to measure the distance
to a nearby star 61 Cygni. He used the technique of parallax, by
measuring the angle to the star when the Earth was on one side of the
Sun, and then measuring it again 6 months later when the Earth was on
the other side.
Over the course of this period, this relatively
closer star moves slightly back and forth against the more distant
background of the galaxy.
And over the next two centuries, other
astronomers further refined this technique, getting better and better
at figuring out the distance and motions of stars.
But to really
track the positions and motions of stars, we needed to go to space. In
1989, the European Space Agency launched their Hipparchus mission, named
after the Greek astronomer we talked about earlier. Its job was to
measure the position and motion of the nearby stars in the Milky Way.
Over the course of its mission, Hipparcos accurately measured 118,000
stars, and provided rough calculations for another 2 million stars.
That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.
Launched
in December 2013, the European Space Agency’s Gaia in is in the process
of mapping out a billion stars in the Milky Way. That’s billion, with a
B, and accounts for about 1% of the stars in the galaxy. The spacecraft
will track the motion of 150 million stars, telling us where everything
is going over time. It will be a mind bending accomplishment.
Hipparchus would be proud.
With the most precise measurements,
taken year after year, the motions of the stars can indeed be
calculated. Although they’re not enough to see with the unaided eye,
over thousands and tens of thousands of years, the positions of the
stars change dramatically in the sky.
The familiar stars in the
Big Dipper, for example, look how they do today. But if you go forward
or backward in time, the positions of the stars look very different, and
eventually completely unrecognizable.
stars look static in the sky, but are they moving? How fast, and how do
we know? What events can make them move faster, and how can humans make
them move?
Support us at: http://www.patreon.com/universetoday
More stories at: http://www.universetoday.com/
Follow us on Twitter: @universetoday
Like us on Facebook: https://www.facebook.com/universetoday
Google+ - https://plus.google.com/+universetoday/
Instagram - http://instagram.com/universetoday
Team: Fraser Cain - @fcain / frasercain@gmail.com
Karla Thompson - @karlaii
Chad Weber - weber.chad@gmail.com
Before we get going, I’d just like to say, happy 300th episode of the Guide to Space. Here’s to hundreds more.
The
night sky, is the night sky, is the night sky. The constellations you
learned as a child are the same constellations that you see today.
Ancient people recognized these same constellations. Oh sure, they might
not have had the same name for it, but essentially, we see what they
saw.
But when you see animations of galaxies, especially as they
come together and collide, you see the stars buzzing around like angry
bees. We know that the stars can have motions, and yet, we don’t see
them moving?
How fast are they moving, and will we ever be able to tell?
Stars,
of course, do move. It’s just that the distances are so great that it’s
very difficult to tell. But astronomers have been studying their
position for thousands of years. Tracking the position and movements of
the stars is known as astrometry.
We trace the history of
astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus
first created a catalog of the 850 brightest stars in the sky and their
position. His student Ptolemy followed up with his own observations of
the night sky, creating his important document: the Almagest.
In
the Almagest, Ptolemy laid out his theory for an Earth-centric
Universe, with the Moon, Sun, planets and stars in concentric crystal
spheres that rotated around the planet. He was wrong about the Universe,
of course, but his charts and tables were incredibly accurate,
measuring the brightness and location of more than 1,000 stars.
A
thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi
completed an even more detailed measurement of the sky using an
astrolabe.
One of the most famous astronomers in history was the
Danish Tycho Brahe. He was renowned for his ability to measure the
position of stars, and built incredibly precise instruments for the time
to do the job. He measured the positions of stars to within 15 to 35
arcseconds of accuracy. Just for comparison, a human hair, held 10
meters away is an arcsecond wide.
Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.
In
1807, Friedrich Bessel was the first astronomer to measure the distance
to a nearby star 61 Cygni. He used the technique of parallax, by
measuring the angle to the star when the Earth was on one side of the
Sun, and then measuring it again 6 months later when the Earth was on
the other side.
Over the course of this period, this relatively
closer star moves slightly back and forth against the more distant
background of the galaxy.
And over the next two centuries, other
astronomers further refined this technique, getting better and better
at figuring out the distance and motions of stars.
But to really
track the positions and motions of stars, we needed to go to space. In
1989, the European Space Agency launched their Hipparchus mission, named
after the Greek astronomer we talked about earlier. Its job was to
measure the position and motion of the nearby stars in the Milky Way.
Over the course of its mission, Hipparcos accurately measured 118,000
stars, and provided rough calculations for another 2 million stars.
That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.
Launched
in December 2013, the European Space Agency’s Gaia in is in the process
of mapping out a billion stars in the Milky Way. That’s billion, with a
B, and accounts for about 1% of the stars in the galaxy. The spacecraft
will track the motion of 150 million stars, telling us where everything
is going over time. It will be a mind bending accomplishment.
Hipparchus would be proud.
With the most precise measurements,
taken year after year, the motions of the stars can indeed be
calculated. Although they’re not enough to see with the unaided eye,
over thousands and tens of thousands of years, the positions of the
stars change dramatically in the sky.
The familiar stars in the
Big Dipper, for example, look how they do today. But if you go forward
or backward in time, the positions of the stars look very different, and
eventually completely unrecognizable.
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