What would happen if the amount of light reaching the Earth from the Sun were cut in half?

What would happen if the amount of light reaching the earth from the sun were cut in half?
The position of the Habitable Zone, as a function of the mass of the star the planets orbit. Image credit:  Chester Harmon , CC A-SA 4.0

The position of the Habitable Zone, as a function of the mass of the star the planets orbit. Image credit: Chester Harmon, CC A-SA 4.0

We’ve tackled a very similar question to this before here at Astroquizzical; check out this post! In that post, we explored what would happen to the Earth if we could slice the Sun in half. And because cutting the Sun’s matter in half doesn’t translate to a slice in brightness of one half, it’s a pretty dramatic shift for our solar system.

However, if we don’t go quite as far with our solar slicing, but instead just drop the brightness of our sun by half, we’ve actually only removed 18% of the mass. This is still a relatively massive star, at 82% the mass of our Sun, but that’s enough to change the distance from the star where liquid water is stable.

As the mass and brightness of a star decreases, that zone of possible liquid water (usually known as the habitable zone) shrinks to a smaller and smaller shell around the star, but because we’re changing the star by a smaller amount this time compared to the earlier post, the habitable zone won’t shrink all the way down to Mercury’s orbit - it would sit closer to where Venus is now. The Earth’s orbit might still fall within the bounds of the habitable zone, but it’d be more in the position that Mars finds itself in now - much colder than Earth now, but able to sustain water under certain circumstances.

Our Sun won't be dropping in brightness anytime soon - on the contrast, as our Sun ages, it becomes slightly brighter, increasing in brightness by about 10 percent every billion years. As it does, the habitable zone around our star has been gradually expanding outwards, and at some point in the next billion years, the Earth will exit the habitable zone entirely.


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How Much Closer To The Sun Does The Moon Travel?

Does the Moon get closer to the Sun than the Earth?
Photographed by an Expedition 28 crew member onboard the International Space Station, this image shows the moon at center, with the limb of Earth near the bottom transitioning into the orange-colored troposphere, the lowest and most dense portion of the Earth's atmosphere. Image credit: NASA

Photographed by an Expedition 28 crew member onboard the International Space Station, this image shows the moon at center, with the limb of Earth near the bottom transitioning into the orange-colored troposphere, the lowest and most dense portion of the Earth's atmosphere. Image credit: NASA

Originally posted on Forbes!

 

In order to tackle this question, we have to understand a bit about the geometry of the solar system, and how both the planets and the moons which orbit those planets behave.

Most of the planets in the solar system circle the Sun in a very thin plane, meaning that if you drew the orbits out on a sheet of paper, you wouldn’t be missing out on any hidden geometry of our solar system. With the exception of Pluto, there’s very little vertical motion in the solar system that would be obscured by drawing it out on flat paper.

The orbit of Triton (red) is opposite in direction and tilted −23° compared to a typical moon's orbit (green) in the plane of Neptune's equator.Image: NASA. Orbital lines: wikimedia user ZYjacklin. Public domain.

The orbit of Triton (red) is opposite in direction and tilted −23° compared to a typical moon's orbit (green) in the plane of Neptune's equator.Image: NASA. Orbital lines: wikimedia user ZYjacklin. Public domain.

Moons are under no particular obligation to follow this pattern, and it’s often thought that if a moon of a particular planet is doing something particularly odd with its orbit, we can use that information to guess that it might have arrived at that planet in an unusual way, rather than forming around that planet. Neptune’s moon Triton is a good example; not only is it angled quite sharply with regards to the plane of the solar system, but it also goes “backwards” - it orbits in the opposite direction of Neptune’s rotation. These have been taken as hints that Triton didn’t form around Neptune, but formed elsewhere, and got trapped around Neptune after being jostled too near to Neptune's gravitational well.

If the Moon happened to orbit in a circle the way a hula hoop rolled on its edge moves, forever tumbling along the direction of the Earth’s travel, then the Moon would never get any closer to the Sun at any point in its orbit. These sorts of orbits aren’t impossible, though in our solar system, they're non-standard.

Our Moon's orbit is, in fact, quite close to perfectly flat with respect to the direction that the Earth travels. It’s tilted by only five degrees relative to Earth’s orbit around the sun. If your arms, like mine, are about six feet from fingertip to fingertip, five degrees is about 3 inches away from horizontal. If you hold both arms out sideways, point one index finger up, and one index finger down, the tips of your fingers are about five degrees offset from the line drawn by your arms.

Earth–Moon system (schematic). Image credit: NASA, arrangement by wikimedia user brews_ohare. Public domain.

Earth–Moon system (schematic). Image credit: NASA, arrangement by wikimedia user brews_ohare. Public domain.

Five degrees of an offset means that the distance between the Moon and the Sun will vary almost exactly by the distance between the Earth and the Moon. Everything is moving in the same plane, so drawing it out on a sheet of paper won't be ignoring much geometry. The Moon’s orbit is also quite close to circular, which again helps with this - there’s no long, comet-like orbit for our Moon, which is why we see it as very nearly the same size in our skies. So with all that behind us, how close could the Moon get?

The Moon orbits the Earth at a distance of about 238,900 miles from our home planet. The Earth, in its turn, orbits the Sun once every year (by definition), at a distance of about 93 million miles from the Sun. Because we know the distance between the Sun and the Earth, and the distance to the Moon from the Earth, if we line everything up just right, then we can place the Moon directly in between the Earth and the Sun. We know this situation happens - this is how we get solar eclipses, when the Moon lines up exactly between the Earth and the Sun.

Annular eclipse. Taken from a 8" Reflector with a solar filter. Image credit: wikimedia user Smrgeog, CC BY SA 3.0

Annular eclipse. Taken from a 8" Reflector with a solar filter. Image credit: wikimedia user Smrgeog, CC BY SA 3.0

This configuration subtracts 238,800 miles off of the 93 million miles which separate the Earth from the Sun. So in the end, even though we have a pretty ideal setup, the Moon can’t ever get that much closer to the Sun. At best, the Moon manages to get a grand total of 0.25% closer to the Sun than the Earth.

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What Does The Sun Sound Like?

What sound does the Sun make, and would it be musical if we could hear it?
This montage of 366 images shows our Sun through the eyes of ESA’s Proba-2 satellite, as seen each day in 2016. The satellite’s SWAP camera works at extreme ultraviolet wavelengths to capture the hot turbulent atmosphere of the Sun, known as the solar corona. Each image was created from 30 separate images centred on 01:00 GMT each day, which were processed to enhance the features extending from the solar disc. Throughout 2016 the Sun’s 11 year activity cycle continued towards its minimum, a period when the number of sunspots, active regions, solar flares and eruptions diminish. Nonetheless, the most active region of last year can be seen in the 17 July image. The bright region close to the centre of the Sun produced eight of the 20 most powerful flares witnessed last year. Other prominent features are coronal holes – darker regions indicating lower levels of emission. However, coronal holes can produce streams of fast solar wind that can trigger geomagnetic storms on Earth. One of the largest holes observed last year can be seen towards the north of the Sun on 24 November, and was present for several solar rotations. Image credit: ESA/Royal Observatory of Belgium

This montage of 366 images shows our Sun through the eyes of ESA’s Proba-2 satellite, as seen each day in 2016. The satellite’s SWAP camera works at extreme ultraviolet wavelengths to capture the hot turbulent atmosphere of the Sun, known as the solar corona. Each image was created from 30 separate images centred on 01:00 GMT each day, which were processed to enhance the features extending from the solar disc. Throughout 2016 the Sun’s 11 year activity cycle continued towards its minimum, a period when the number of sunspots, active regions, solar flares and eruptions diminish. Nonetheless, the most active region of last year can be seen in the 17 July image. The bright region close to the centre of the Sun produced eight of the 20 most powerful flares witnessed last year. Other prominent features are coronal holes – darker regions indicating lower levels of emission. However, coronal holes can produce streams of fast solar wind that can trigger geomagnetic storms on Earth. One of the largest holes observed last year can be seen towards the north of the Sun on 24 November, and was present for several solar rotations. Image credit: ESA/Royal Observatory of Belgium

Originally posted on Forbes!

Sound is a tricky thing in space. Sound is a pressure wave, an oscillation in the density of air or water, which moves through the air or through water until it reaches something it can rattle. If that sound is reaching a human ear, and if the oscillation is within the range of frequencies we are sensitive to, it will be heard. Our Earth produces a number of these pressure waves, from the sound of a person next to you speaking, or the crash of a wave on a beach, or a sonic boom of an airplane above you. However, there are plenty of sounds produced which we are outside our range of hearing - with an instrument tuned to receive those pressure waves, we can prove their presence, but it would be impossible to play back and hear it without speeding up the recording.

In space, we have a major problem with recording sounds; there’s no atmosphere for sound waves to travel through, so any pressure waves an object may be producing will be instantly silenced without a medium to compress. However, if you’re clever about it, there are other ways of recording information which can be translated into a sound; the easiest one is vibrations. The ‘crunch’ of Philae, Rosetta’s lander on the comet 67P, hitting the surface of the comet made the rounds - but this noise is not, in fact, the result of a microphone on the landerThis noise is a translation of the vibrations of the feet of the lander at the moment when it hit the surface of the comet.

Rosetta’s lander Philae has been identified in OSIRIS narrow-angle camera images taken on 2 September 2016 from a distance of 2.7 km. The image scale is about 5 cm/pixel. Philae’s 1 m-wide body and two of its three legs can be seen extended from the body. The images also provide proof of Philae’s orientation. A Rosetta Navigation Camera image taken on 16 April 2015 is shown at top right for context, with the approximate location of Philae on the small lobe of Comet Churyumov-Gerasimenko marked. Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/NavCam, CC BY-SA IGO 3.0

Rosetta’s lander Philae has been identified in OSIRIS narrow-angle camera images taken on 2 September 2016 from a distance of 2.7 km. The image scale is about 5 cm/pixel. Philae’s 1 m-wide body and two of its three legs can be seen extended from the body. The images also provide proof of Philae’s orientation. A Rosetta Navigation Camera image taken on 16 April 2015 is shown at top right for context, with the approximate location of Philae on the small lobe of Comet Churyumov-Gerasimenko marked. Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/NavCam, CC BY-SA IGO 3.0

However, if you want to translate a data set into sound, you’re not limited to just dealing with vibrations. You can turn pretty much anything into a set of tones, if you’re creative enough. Sonification is a booming area of data manipulation -- it’s another face of the data visualization scene; instead of presenting the information visually, you can code it audibly, and listen to it over time. You simply have to decide what you want the pitch of the musical note to correspond to, what you want the timing between each note to correspond to, and what you want the volume to correspond to.

For data coming from a spacecraft which monitors the Sun, there is often a new image every hour and a half or so. In this case, the pacing between notes is easily given to the time between observations, which will form a regular cadence. However, extracting a volume and pitch out of the data will depend very much on exactly what part of the data you’re interested in reflecting.

For Rosetta’s “singing comet” sonification, there was a very low frequency oscillation in the magnetic field surrounding the comet, measured by Rosetta. The decision here was to use the frequency of that vibration in the magnetic field as the pitch, but sped up by a factor of 10,000, so that it could register in the human ear. The volume here is driven by how large the oscillations were, much as it would be for a sound wave on Earth.

Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across. Image credit: ESA/Rosetta/NavCam –  CC BY-SA IGO 3.0

Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across. Image credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

For the Sun, not only do we have to speed up the oscillation, but we also have to choose which observed oscillation we want to convert into a sound. The most common choice that I found was to examine the roiling surface of the Sun, which resembles nothing more than a pot of water at high boil. You could imagine examining how high the bubbles rise above the surface, and how quickly they do so. If we convert this amplitude and rapidity into a volume and a tone, we can get a musical note out for every bubble that rises to the surface. This is only one of many possible optionsfor sonifying the Sun, but it seems to be one of the more common choices.

What do we hear? Here’s a few examples.

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Would A Brown Dwarf Near Us Cook The Earth?

 

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Could You Go Surfing On The Sun?

If you had the right protective clothing, could you go surfing on a solar flare?
On April 17, 2016, an active region on the sun’s right side released a mid-level solar flare, which can be seen in this image as a bright point of light. Credits: NASA's Goddard Space Flight Center/SDO/Genna Duberstein

On April 17, 2016, an active region on the sun’s right side released a mid-level solar flare, which can be seen in this image as a bright point of light. Credits: NASA's Goddard Space Flight Center/SDO/Genna Duberstein

Originally posted on Forbes!

Well, we’re going to have to assume that our protective clothing is magical, because as far as I know, when you’re dealing with something hot enough to vaporize iron, I don’t think the type of protection you’re hoping for exists. But we can certainly ignore the melting factor when looking into whether or not you could go surfing on the Sun.

Surfing on the Earth works on a few principles; first, we have waves in our oceans; and second, surfboards are very good at floating on our oceans. It’s the second one of these that’s going to cause us the most trouble. Not only does the Sun have solar flares, but solar tsunamis also appear occasionally on the surface of the Sun. Solar tsunamis are usually triggered by some kind of solar flare-up, and can rise thousands of kilometers above the surface of the Sun - these tremendous shock waves are bigger than our entire planet.

On August 1st, almost the entire Earth-facing side of the sun erupted in a tumult of activity. There was a C3-class solar flare (white area on upper left), a solar tsunami (wave-like structure, upper right), multiple filaments of magnetism lifting off the stellar surface, large-scale shaking of the solar corona, radio bursts, a coronal mass ejection and more. This multi-wavelength (211, 193 & 171 Angstrom) extreme ultraviolet snapshot from the Solar Dynamics Observatory (SDO) shows the sun's northern hemisphere in mid-eruption. Different colors in the image represent different gas temperatures ranging from ~1 to 2 million degrees K.  Credit: NASA/SDO/AIA

On August 1st, almost the entire Earth-facing side of the sun erupted in a tumult of activity. There was a C3-class solar flare (white area on upper left), a solar tsunami (wave-like structure, upper right), multiple filaments of magnetism lifting off the stellar surface, large-scale shaking of the solar corona, radio bursts, a coronal mass ejection and more. This multi-wavelength (211, 193 & 171 Angstrom) extreme ultraviolet snapshot from the Solar Dynamics Observatory (SDO) shows the sun's northern hemisphere in mid-eruption. Different colors in the image represent different gas temperatures ranging from ~1 to 2 million degrees K. Credit: NASA/SDO/AIA

But could you surf one? Ignoring the inadvisability of such an endeavor on so many fronts, let’s look at the physics of floating on a surfboard. Most surfboards are made of very light materials - which makes them much, much less dense than water. They have to be, because the surfer would like their surfboard to still remain above water when they’re standing on top of it, and so the surfboard has to resist sinking well enough that the weight of the board, plus the weight of the surfer, doesn’t submerge the board. The average human is slightly more dense than fresh water, so the surfboard is stuck doing all the heavy lifting.

The buoyancy of an object is the fundamental piece of physics which determines if something sinks, floats, or hangs neutrally in the middle. This last is the goal of a scuba diver, but a surfer wants to float. Buoyancy is usually described in terms of liquid displacement; if you take an empty 2 liter bottle, and submerge it in water, you had to move 2 liters worth of water to make room for the bottle. 2 liters of water weighs about 4 and a half pounds (2 kilograms exactly), so you could fill that bottle with anything you like, as long as it weighs less than four and a half pounds, and it will float. Fill it with something (rocks, for example) which weighs more than 4 and a half pounds, and it’ll sink.

Surfboards are often filled with polystyrene (packing peanut material), so they’re pretty close to the empty 2 liter bottle end of our experiment above. If you submerge a surfboard that displaces 65 liters of water, on the Earth, you get a buoyant force of some 638 Newtons in the 'out of the water' up direction. Gravity pulls down on it with only 29 Newtons of force (assuming a 3 kilogram / 6 pound board), so buoyancy wins, and it floats.

This image, captured in December 2010 by NASA’s Solar TErrestrial RElations Observatory (STEREO) spacecraft, shows a solar filament almost one million miles long. Filaments are elongated clouds of cooler gases suspended above the sun by magnetic forces. They can be unstable and often break away from the surface.  Credits: NASA

This image, captured in December 2010 by NASA’s Solar TErrestrial RElations Observatory (STEREO) spacecraft, shows a solar filament almost one million miles long. Filaments are elongated clouds of cooler gases suspended above the sun by magnetic forces. They can be unstable and often break away from the surface. Credits: NASA

If we want to go surfing on the Sun, we still need to float. Here’s the problem: the Sun is way less dense than water. Particularly at the surface, where you get your solar tsunamis and your solar flares, the density of the solar atmosphere is a million times less dense than air at sea level. It is a billion times less dense than water.

If you take a normal surfboard and a normal human male according to the 1960s, the average density between them is 554 kilograms per cubic meter. This is significantly less than the 1000 kg per square meter for water, so you’re safe to float in water. But 554 is ten million times too dense for the solar atmosphere. You have no hope of floating on the surface of the Sun. You would drop like a very heavy rock, deep into the Sun.

What to do? If you wanted to get the same buoyant upward force from the Sun, clocking in at a density of 10-6 kilograms per cubic meter, as you did from water on Earth (which has a density of 1000 kilograms per cubic meter), how big would your surfboard need to be? Well, let’s plug things back into our equation. We know the gravitational force at the surface of the Sun, the density of the solar atmosphere, and we need the volume of the solar surfboard. This works out to needing a surfboard which has 36 times the volume of a standard surfboard. It means a surfboard which is 2.5 inches deep by 4 feet wide by 86 feet long.

And that’s just to get the same upward force - it says nothing about whether the surfboard sinks or floats. How light would it have to be to float in the solar atmosphere? To match the density of the solar photosphere, our 86 foot surfboard would have to have a mass of less than 2.3 milligrams, and that’s without a rider. 2.5 milligrams is approximately the weight of a mosquito, or a few grains of sand. To add an 80 kg rider, and give yourself another 80 kg for surfboard infrastructure, you’re looking at a barge 5cm thick, and 54 kilometers square - just shy of trying to surf Manhattan Island. Once again, this one is a non-starter- you’d have a hard time catching any kind of wave on a craft like that.

No surfing the Sun.

Read the full article on Forbes!

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