There
ya go. Now, the 'twinkling starlight' I'll be mainly talking about is
related to exoplanets, or planets orbiting stars other than our own.
If you look carefully at stars from outside our atmosphere, or
correct for atmospheric effects, the stars still
twinkle, but for what I think is a much more interesting reason.
Do you want to know something interesting about starlight?
Great!
For
the longest time, it was thought that our planet and our solar system
were pretty unique. Aristotle laid down the thinking about many
topics including astronomy for many centuries, and as it turns out he
was wrong about a fair bit of it. While understandable for his time,
by the 1600's, times were changing. In the early 1600's Galileo
looked up at the moon with a telescope he made (didn't invent) and
observed the moon's terminator, the area where light met dark. In the
shadows he saw craters, bumps, and ridges; the moon wasn't a perfect
celestial orb, it was its own world with its own unique features.
Couple that with his discovery of moons orbiting Jupiter, and we were
on our way to discovering other worlds, inferred from points of
light.
 |
*IC6.G1333.610s, Houghton Library, Harvard University
moons were published by Galileo in 1610 in this pamphlet. |
We
have now sent spacecraft to nearly all of the thirty or so largest
bodies in the solar system. With missions visiting the asteroids
Vesta and Ceres, and the upcoming mission to Pluto, New Horizons, our
curiosities about other worlds just took steps much farther afield.
Just
as we could see other worlds in our own solar system, we can now look
for worlds orbiting other stars using several methods of analyzing
flickering starlight from their home star. With few exceptions, we
cannot just take pictures of the planets because their star outshines
them by many orders of magnitude, what we can see it the influence
they have on their star.
Transit method -
One
way to detect exoplanets is too find a planet that passes directly
between its home star and us here on earth. A bit like a solar
eclipse. When this happens, the planet blocks a little bit of the
light, and the star dims. We can track the stars brightness and if it
dims consistently and periodically we can tell that there is probably
a planet orbiting that star. Here is what one of these dips looks
like:
 |
Image: Nikola Smolenski
|
The transit method is currently by far the most common way to detect exoplanets, but it has its drawbacks. Due to the fact that the planet has to pass between the star it is orbiting and the observer here on earth, it biased toward planets that orbit "edge - on" to us here on earth. Imagine flipping a coin, and taking a picture when the coin is exactly edge-on. Most of the pictures are going to show at least some of either the heads side or the tails side. This is roughly the same probability as a particular star system appearing exactly edge on to ours so the planet passes in front of the sun.
This method tends to be biased in finding large planets orbiting close to their stars. The larger and closer to its star that a planet is, the more likely it is to cross in front of the star and dim the light we see. These planets are known as "hot Jupiter" because they tend to be larger than Jupiter and closer to their star than Mercury is to our sun. This flies in the face of how we think planets developed, suggesting that hot Jupiters are quite rare. If this is the case, there could many, many more planets out there than we can currently find using this method.
It is important to note at this point that we cannot see the outline of the planet in front of the star. The only thing we can detect from here on earth is the slight dimming from a distant point of light.
Two more ways I'll briefly touch on on the radial velocity method and something called astrometry.
To describe the radial velocity method I first have to talk about the Doppler effect.
<sidenote>
I always thought "Christain Doppler and the Effects" would make a great band name
</sidenote>
There are plenty of great video about how this works, so I'll only go into it very briefly here. When a noise-making object approaches you, the sound waves "stack up" and compress on their way to your ears. This registers as a higher pitch. When the noise-making object moves away from you the sound waves "stretch out" and you register this as a lower pitch. This is why cars passing you make the characteristic "weeeee-yahhhhhh" sound.
The same goes for light. When an object is moving toward you, you register the compression of the waves as a "blueshift," the object literally looks a bit bluer. When the object travels away, the light looks redder, a "redshift."
TL;DR: Stars look bluer moving toward you, redder when they're moving away.
Alright, on to radial velocity. A large planet orbiting a star will cause the star to wobble a little bit, as seen below:
This is because the planet gravitationally tugs on the star, just as the star tugs on the planet. Notice how the star moves up and down. If we look at this star from earth, we can see it getting redder and bluer as it travels farther and closer to us, and from that, infer the presence of a planet by looking at the rate of the wobble.
On to Astrometry!
If you imagine looking at the system above from earth just as it is portrayed, you would see the star travelling in a little circle. If you look at both the foreground star as well as background objects, you can see the motion of the star and from that find out characteristics of the planet orbiting it.
This topic is difficult to convey through writing alone, so if you're interested check out YouTube for some great videos about exoplanets and exoplanet detection. Here are a few of my favorites:
Overall, it is truly amazing what we can discover merely by looking at twinkling starlight.
Cheers,
- Scott
LINKSTORM:
IS THIS REAL LIFE?
An astronomy mystery solved - why the sun's corona is so hot
Leonardo Da Vinci's Resume
New from Tesla!
Ice cream in space
The Mythbuster's dummy Buster goes to space (not space, but at least... up)!
Email subscription:
tinyletter.com/scottsieke
It is important to note at this point that we cannot see the outline of the planet in front of the star. The only thing we can detect from here on earth is the slight dimming from a distant point of light.
Other Methods
Two more ways I'll briefly touch on on the radial velocity method and something called astrometry.
To describe the radial velocity method I first have to talk about the Doppler effect.
<sidenote>
I always thought "Christain Doppler and the Effects" would make a great band name
</sidenote>
There are plenty of great video about how this works, so I'll only go into it very briefly here. When a noise-making object approaches you, the sound waves "stack up" and compress on their way to your ears. This registers as a higher pitch. When the noise-making object moves away from you the sound waves "stretch out" and you register this as a lower pitch. This is why cars passing you make the characteristic "weeeee-yahhhhhh" sound.
The same goes for light. When an object is moving toward you, you register the compression of the waves as a "blueshift," the object literally looks a bit bluer. When the object travels away, the light looks redder, a "redshift."
TL;DR: Stars look bluer moving toward you, redder when they're moving away.
Alright, on to radial velocity. A large planet orbiting a star will cause the star to wobble a little bit, as seen below:
This is because the planet gravitationally tugs on the star, just as the star tugs on the planet. Notice how the star moves up and down. If we look at this star from earth, we can see it getting redder and bluer as it travels farther and closer to us, and from that, infer the presence of a planet by looking at the rate of the wobble.
On to Astrometry!
If you imagine looking at the system above from earth just as it is portrayed, you would see the star travelling in a little circle. If you look at both the foreground star as well as background objects, you can see the motion of the star and from that find out characteristics of the planet orbiting it.
This topic is difficult to convey through writing alone, so if you're interested check out YouTube for some great videos about exoplanets and exoplanet detection. Here are a few of my favorites:
Overall, it is truly amazing what we can discover merely by looking at twinkling starlight.
Cheers,
- Scott
LINKSTORM:
IS THIS REAL LIFE?
An astronomy mystery solved - why the sun's corona is so hot
Leonardo Da Vinci's Resume
New from Tesla!
Ice cream in space
The Mythbuster's dummy Buster goes to space (not space, but at least... up)!
Email subscription:
tinyletter.com/scottsieke
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