rupees88

So what you are telling me is that it's a racecar.

Rev. Rob Large

iTrader: (11)

But less money.

Today, right now in fact, the interior planet of Mercury is transiting across the disc of the Sun, relative to our view of it—it is passing directly between us and the Sun. This is really interesting and not-all-too-often-occurring event. As Mercury passes in front of the Sun, the Sun’s luminosity, or apparent brightness, will decrease as Mercury partially blocks the Sun’s light output as seen here on Earth (about 0.3% decrease). Although only a fractional decrease, it is still detectable.



This is one of two primary methods to detect extrasolar planets and binary star systems—transit photometry.
Photometry is the measurement of light output from celestial objects, primarily stars. Since the only direct measurement we can make of objects not within our “reach” is how bright they are, photometry is the foundation of all astronomy.

The first detection of extrasolar planets was made by looking at the radial velocities of stars locally within our galaxy. Radial velocity is the speed at which an object is moving either towards or away from the observer along their line of sight. Due to the Doppler Effect, as the star moves towards us, the wavelengths of the light emitted would compress (blue shift) and, as the star moves away, the wavelengths would expand (red shift). Since every element on the periodic table has very well-known characteristic wavelengths, with hydrogen being the most predominant, it was simply a matter of looking for the characteristic spectral lines and measuring how much they have shifted (either bluer/shorter or redder/longer) to determine whether the star is moving towards or away from us. In measuring the velocities of several objects over time, it was discovered that some stars’ velocities would fluctuate (speed up and slow down) with a regular period or frequency. This happens when the star has an object(s) orbiting around it and the gravitational interaction with that object(s) causes the star to “wobble” back and forth. This was the prevailing methodology for extrasolar planetary detection from the first confirmation (around 1989) up through about 2010.

In 2009, the Kepler telescope was launched with the primary mission of collection photometric measurements of stars in the Cygnus constellation. With the influx of photometric data from Kepler, the most productive method for extrasolar planet detection shifted (no pun intended) away from radial velocity/Doppler spectroscopy detection and moved towards transit detection. Taking measurements of the apparent luminosity of an object and plotting over time is called a “light curve”.

Simulations:




Actual light curve from Kepler data:


From the light curve, you can extrapolate all kinds of information about the planetary system, including exoplanet diameter and orbital period. Plotting the light curves of hundreds of thousands of stars, the number of exoplanet candidates detected skyrocketed, from a few hundred ever detected through 2010, to over 3,000 in the span of 36 months.
One of the fascinating, and arguably most important, bits of information that can be extrapolated from transit photometry is the ability to determine the chemical or elemental composition of the atmospheres of these exoplanet. Remember how we said that every element has its own characteristic spectral wavelengths? This goes for both emission and absorption of light. If a continuum of light were passed through a cloud of hydrogen, the light coming out the other side of the cloud would have all wavelengths present except for the characteristic spectral wavelengths of hydrogen since those wavelengths were absorbed by the hydrogen in the cloud. When light from the star is emitted, it is, for the most part, continuous across all wavelengths of light. When that light passes through the atmosphere of the exoplanet, all of the elemental gasses in the atmosphere will absorb their characteristic spectral wavelengths while all other wavelengths will pass right through. Simply look at the continuum and see which lines are missing and voila! You have the chemical composition of the atmosphere of your exoplanet.

Pretty picture:


Why is this important? Well, what if you were looking for a planet with a specific chemical composition, oh say, a planet with an atmosphere composed of mostly nitrogen, oxygen and some water, perhaps?

That’s enough. My senior projects were on both stellar photometry AND spectroscopy so I could go on and on about both topics.

Rev. Rob Large

iTrader: (11)

That's because the damn thing weighs nothing. Most of Team Moist could probably lift one off the ground.

stupidchicken03

iTrader: (38)

Thurs?

Rev. Rob Large

iTrader: (11)

I'm down.

UnderTheRadar

iTrader: (1)

Blasphemy...one cannot hate Moist

Why Do You Hate The Word Moist? Science.

stupidchicken03

iTrader: (38)

So, with the planet coming between us and the Sun, even those its a small percentage, you say its noticeable. Is that noticeable to the "naked eye" aka people in general, or just to equipment?

Would that have anything to do with today's weather being cooler and the next couple days spike up?


Kinda interesting at seeing the end result of what can be detected and concluding what didnt come through to know what that (atmosphere or whole planet?) consists of.

Rev. Rob Large

iTrader: (11)

Well, first and obviously, never look right at the Sun under any condition. Galileo found that one out the hard way. He went blind from his solar observations with a telescope and no solar filter.

With a rudimentary solar filter (tinted glass ~10% transmission) and a binoculars, you should be able to see the dot. The attachment below is a picture my colleague at Sac State took today with a small 4" inch telescope, transmission filter and his cellphone. lol You can see Mercury's small silhouette against the Sun about the 9:00 position about 20% in from the edge.

For exoplanet detection, since the systems are so far away, the only way the apparent luminosity fluctuations can be detected is via instruments. The brightnesses are too low and the apparent size of the stars and planets are too low for the human eye.

No, the decrease in brightness is less than 1% and it's only for a few hours.

It's mostly the atmosphere. The denser parts of the planet's composition do allow light to pass through them--in effect, they absorb everything so the spectrum is just.. black. lol

stupidchicken03

iTrader: (38)

Do any of the known planets (in any solar system) have similar atmospheres to Earth's?

Rev. Rob Large

iTrader: (11)

I don't know the exact number, but there have been exoplanets discovered with atmospheres similar to Earth.

But, it's not just about atmosphere..

The "Goldilocks Zone" is the physical distance range a planet can be in, given the size of the host star, in which water is liquid. You can have an Earth-like exoplanet with comparable concentrations of atmospheric oxygen and water, but if it's too far out and everything is frozen, then it's not habitable. Same goes for planets too close to the host star where everything is too hot.

One other consideration is the size and density of the exoplanet. If the planet is too big and dense, extreme gravitational force of the planet would crush any human being trying to live on it.

Thinking of moving? lol

i<3dirt

iTrader: (1)

i guess ill bring the car

The Law

What's for lunch?

UnderTheRadar

iTrader: (1)

Knowledge...

rupees88

In your professional opinion do you think we could lift it into a pool? For science of course...

stupidchicken03

iTrader: (38)

Hasnt everyone? lol


nom nom nom
dont tell sybir