This episode of Real Engineering is brought to you by Skillshare, home to over 20,000
classes that could teach you a new life skill.
Staring at the sky in awe is one of the few quintessential human experiences.
Gazing into the vast emptiness of space wondering where our place in the universe stands.
For millennia the mystery of these celestial bodies captivated the human mind, seeding
religions and mythical stories.
We couldn’t ignore the moon above us, influencing our tides, or the sun, our benevolent provider,
burning in the blue sky.
At night, individual stars melded together into a boundless blanket of glittering light,
until we began to notice patterns in their chaos, guiding us as we explored our world.
These star maps helped us make a monumental discovery, some stars in the sky moved differently
to others.
Wandering through the night sky, planets like ours orbiting our sun.
Mercury, Venus, Mars, Jupiter and Saturn, all visible to the naked eye were discovered
this way by ancient babylonian astronomers over 4 thousand years ago.
Later Galileo improved the telescope, allowing him to observe even fainter points in the
sky, invisible to the naked eye.
He discovered Jupiter's moons.
Ganymede, Callisto, Io and Europa and Saturn’s moons soon followed mostly discovered by Cassini.
Uranus & Neptune had been observed numerous times through telescopes, but astronomers
continually mistook them them for stationary stars or comets.
It was only when astronomers noticed the circular orbit of Uranus that it was accepted as a
planet.
Then as it’s orbit was further examined astronomers noticed deviations, that could
only be caused by a nearby planet, and thus Neptune, our solars systems final planet,
was discovered *on screen joke - Sorry Pluto*
It tooks thousands of years to just discover the planets in our solar system, but in the
last 30 years we have discovered over 3717 planets orbiting stars so far away that we
will never be able to visit them with current technology.
Perhaps the most fascinating planetary system we have discovered is that of Trappist-1,
an ultra-cool dwarf star located 40 light years away from our Sun, which has not only
1 temperate terrestrial planet, but 7.
Each of the planets are rocky and between the size of Earth and Mars.
The star is small and cold compared to ours, but the planets orbit so closely to the star,
closer than mercury orbits the Sun, that they all have the possibility of containing liquid
water.
This is a lot of information about planets that we can’t even see directly.
So how do present day astronomers find these, relatively speaking, tiny objects floating
in space?
The first planets discovered orbiting this star were discovered by a Belgian team using
the Trappist-south telescope located high the Chilean mountains.
The team had their telescope trained on the dwarf star waiting for a dimming of it’s
light, a tell tale sign of a planet in orbit passing in front of the star, and thus blocking
some of it’s light.
But how have we discovered so much about this system, simply by a dimming of light in its
star?
If we calculate the distance to the star, using the parallax method, we can discover
a lot more about the planets passing in front of it.
You can see how the parallax method works right now by holding your thumb in front of
you with one eye open.
Now close that eye and open the other.
Did you notice it appeared to move relative to the background, this is called parallax
and we can use it to measure the distance to a star,
but instead of closing our eyes and staring at the sky, we take measurements of the planets
position from opposite sides of our orbit around the sun.We know the distance between
these two points, and we can measure the change in the stars position relative to distant
stars behind it, giving us the parallax angle, thus we have all the information we need to
calculate the distance to the star using some simply trigonometry.
Now that we know the distance to the star, we can calculate its mass and size by observing
its apparent brightness and temperature observed from earth.
We have models for how stars form, with massive stars being hotter and brighter than smaller
stars, and so by measuring these values we can get a lot of information about the star.
That’s how we know Trappist-1 is an ultra-cool dwarf star.
Now that we know more about the star, we discover what we are really interested in.
The planets size, mass, and whether it resides in the goldilocks zone where humans could
survive.
To do that we need to know how far away the planet is from the star.
We do this using Kepler’s Third Law which looks like this.
It tells us the orbital period for planet, that’s how long it takes to orbit it’s
star.
Here G is the Newton’s Gravitational Constant, capital M is the Star’s mass, lowercase
m is the planet’s mass, and a is the orbital radius.
We can ignore the planet’s mass for now, as it’s miniscule compared to the star’s.
If we do this for Earth, it introduces an error of just 0.001%.
The period is measured by seeing the time between transits, and so we have all the variables
we need to calculate the orbital radius.
Now that we know how far away the planet is, figuring out it’s diameter from the transit
dimming is simple.
The next bit of information gathering requires a bit of a perspective shift.
We are used to the idea that planets orbit a star, but it would be more accurate to say
that the planet and star orbit the centre of mass of the star-planet system, which is
not at the centre of the star.
This means the planet’s mass is actually impacting the orbit of the star around this
point.
The larger the mass of the planet the larger the deviation.
We can measure the magnitude of this deviation by detecting the doppler shift in the stars
light frequency.
As the star moves towards us the light becomes slightly more blue, and when the star moves
away from us it becomes slightly more red.
Using the law of conservation of momentum we can easily calculate the mass of the planet.
We know the velocity of the planet from orbital radius and period measurements, the mass of
the Star from our distance and luminosity measurements, and the velocity of the sun
is measured from these doppler shifts in the light frequency.
Leaving us with all the information we need to calculate the mass of the planet.
Using these tools Astronomers have inferred quite a lot of information about these planets.
The 7 planets orbit so closely to their star that a year ranges from just 1.5 days for
the innermost planet to 20 days for the outermost planet.
They are so close packed that the planets will at times appear in each others sky, larger
than our moon appears in ours.
Maybe the coolest part of the entire thing, is the planetary system is named after the
beer the scientist used to toast their discovery.
But it isn’t all good news, because they orbit so close, many of the planets will be
tidally locked, like our moon is to the earth, meaning one side of the planet will constantly
face the sun.
Which may restrict life to the terminator, the narrow band of perpetual twilight.
On top of this, orbiting this closely to a dwarf star exposes it to radiation from solar
flares, which can strip it’s atmosphere away, especially if it is not protected by
a strong magnetic field like earth.
For now, we don’t have a lot of information on these planets, beyond their position, period
and mass.
But we’ll know more soon, as the James Webb Telescope will be able to give us more information
about the atmosphere on these planets by observing the light that shines through their atmosphere
during transit.
By examining the spectrum of light coming through the atmosphere we can discover what
gases are in its atmosphere.
Here we have the spectroscopy analysis of Venus, Earth and Mars.
All have the fingerprints of carbon dioxide in their atmosphere, while only Earth has
the traits of an atmosphere rich in ozone and water.
If we see results like these coming from any of the Trappist-1 planets, a world wide toast
with Belgian beers may be in order.
Learning how astronomers discover our universe is fascinating, but it’s unlikely you will
ever have the tools to discover your own worlds, but you can explore the world you stand on
and its night time sky using fairly inexpensive equipment to produce incredible photos like
this.
You can learn how to do this using this course on Skillshare, which will teach you how to
find the best times of month plan your shoot, how to find dark areas near your location,
how to identify and plan the stars you will photograph and how to set up your equipment.
This is probably my favourite course I have taken on Skillshare to date, and I bet you
will like it too.
These days you can teach yourself pretty much any skill online and Skillshare is a fantastic
place to do it.
With professional and understandable classes, that follow a clear learning curve, you can
dive in and start learning how to do the work you love.
. A Premium Membership begins around $10 a month
for unlimited access to all courses, but the first 1000 people to sign up with this link
will get their first 2 months for free.
So ask yourself right now.
What skill have you been putting off learning.
What project have you been dreaming of completing, but you aren’t sure if you have the skills
to do it.
Why not start right now and sign up to Skillshare using the link below to get your first 2 months
free.
You have nothing to lose and a valuable life skill to gain.
As usual thanks for watching and thank you to all my Patreon supporters.
If you would like to see more from me, the links to my twitter, facebook, discord server,
subreddit and instagram pages are below.