Starship Asterisk*

by **Fred the Cat** » Tue Sep 13, 2016 4:06 pm

geckzilla wrote:
MarkBour wrote:
geckzilla wrote:It's a good enough approximation for me to say that yes, that crescent at that position is impossible, given their orbital parameters. The planet would have to be a fraction of its distance from the star for it to appear in crescent phase at that position.
Ah .... at that position. I thought you were saying the outer planet would never see a crescent phase for the inner planets. That's what had me scratching my head.
Oh, heh. Yeah, it'd be far, far, off the picture in crescent phase.

I was just watching about exoplanets and a video clip pictured a scene like this days APOD. It showed the exoplanet transit then leave the bright disc. There was a moment, just after, when a brief flash came off of the planet's surface. It triggered my mental picture on how we use light from a sun to gather information about the planet - whether it's in our solar system or in one a long ways away.

How you might dissect that flash into small time divisions and analyze it's changing information is pretty mind boggling. If we could ever block the bright star's light to see that flash would be mind altering.

by **geckzilla** » Fri May 13, 2016 12:26 am

MarkBour wrote:
geckzilla wrote:It's a good enough approximation for me to say that yes, that crescent at that position is impossible, given their orbital parameters. The planet would have to be a fraction of its distance from the star for it to appear in crescent phase at that position.
Ah .... at that position. I thought you were saying the outer planet would never see a crescent phase for the inner planets. That's what had me scratching my head.

Oh, heh. Yeah, it'd be far, far, off the picture in crescent phase.

by **MarkBour** » Fri May 13, 2016 12:08 am

geckzilla wrote:It's a good enough approximation for me to say that yes, that crescent at that position is impossible, given their orbital parameters. The planet would have to be a fraction of its distance from the star for it to appear in crescent phase at that position.

Ah .... at that position. I thought you were saying the outer planet would never see a crescent phase for the inner planets. That's what had me scratching my head.

by **Chris Peterson** » Sun May 08, 2016 4:18 pm

moonshiner wrote:an artist's rendering is exponential to envisioning unknown planets. it is a candle piercing the elusive night..a stepping stone from which the intellect builds models and draws conclusions. the experienced mind may thus examine the possibilities based on what is known of planetary science at home..in the solar system.

Nevertheless, our knowledge of optics and our ability to model real physical systems means that we should expect renderings of astronomical scenes to be physically accurate. That does not preclude the invention of imaginative, speculative scenery. But image scale, color, lighting, shadows, atmospheric effects- these things should be- and can be- accurately rendered.

by **moonshiner** » Sun May 08, 2016 4:08 pm

an artist's rendering is exponential to envisioning unknown planets. it is a candle piercing the elusive night..a stepping stone from which the intellect builds models and draws conclusions. the experienced mind may thus examine the possibilities based on what is known of planetary science at home..in the solar system.

it may be inferred that planets bound to a red dwarf star continually face the same side to the parent star in the same way that the moon faces the earth. such red dwarf planets endowed with substantial atmospheres would likely have a very distinct weather cycle with an overdrive of storms and lightning.

a hemisphere of a terrestrial red dwarf planet would be continually subject to light and the other hemisphere immersed in eternal night..and possibly eternal cold. a ghastly fierce landscape all year round; probably not the kind that would yield soothing wine and poetry.

by **geckzilla** » Sun May 08, 2016 3:52 am

MarkBour wrote:
geckzilla wrote:I toyed around with the system parameters in Blender to see what was possible. You can maximize their size disparity by putting TRAPPIST-1d at its closest possible semi-major axis, having TRAPPIST-1b transit the star and TRAPPIST-1c in conjunction behind the star. 1c will look much smaller than 1b at that point.
Blender is just rendering software, right? It does not help with questions of the possible orbits, does it? You claimed that the planets could never be aligned as shown in the APOD ... specifically that 1c could never appear as a crescent from 1d. Why do you say that?

Because distance and scale in space are not intuitive and because I am a visual learner, I use Blender to create a model of the system and simulate how the light from the star illuminates each planet. It's something I started doing some time ago when I realized how wrong my brain had some things. It's a good enough approximation for me to say that yes, that crescent at that position is impossible, given their orbital parameters. The planet would have to be a fraction of its distance from the star for it to appear in crescent phase at that position.

by **MarkBour** » Sun May 08, 2016 3:28 am

geckzilla wrote:I toyed around with the system parameters in Blender to see what was possible. You can maximize their size disparity by putting TRAPPIST-1d at its closest possible semi-major axis, having TRAPPIST-1b transit the star and TRAPPIST-1c in conjunction behind the star. 1c will look much smaller than 1b at that point.

Blender is just rendering software, right? It does not help with questions of the possible orbits, does it? You claimed that the planets could never be aligned as shown in the APOD ... specifically that 1c could never appear as a crescent from 1d. Why do you say that?

by **geckzilla** » Sun May 08, 2016 2:56 am

MarkBour wrote:Still, the sizes shown in the sky seem possible to me. It should look like a couple of Earths near a Jupiter, right?

From a position other than TRAPPIST-1d, yes, one looking significantly larger than the other is possible if you were close enough to it. Like this. Get farther away and you'll get a scene like this. So from 1d, the distance is great enough that the two wouldn't appear so disparate. I toyed around with the system parameters in Blender to see what was possible. You can maximize their size disparity by putting TRAPPIST-1d at its closest possible semi-major axis, having TRAPPIST-1b transit the star and TRAPPIST-1c in conjunction behind the star. 1c will look much smaller than 1b at that point.

by **MarkBour** » Sun May 08, 2016 2:45 am

oldrcd wrote:PLEASE lose the "artists conception" illustrations. They are rampant nonsense; they ignore physics.
There are "millions" of amazing astro-photos. You don't need invented artwork.
I recommend apod.com to people who can learn the reality. If you keep adding non-scientific artwork, I'll stop recommending this site.

aljo wrote:Is anyone else irritated by the lack of realism of the image? The right hand moon is blotting out the light from the sky, even though the moon is much further away, which is obviously impossible.

I believe I see where both of you are coming from, but please consider the following. This is a fantastic astronomical discovery, and will result in a lot of further investigation. APOD could easily have put up an image from TRAPPIST itself, and I think they've had a superb mix of imagery types over time. But these worlds have captured our imagination in alignment with a deep and abiding quest of the human race. To get at that, a luminosity graph will never do. This view, which obviously had to be artist-rendered, is every bit as worthy of our consideration as other APODs. And I see it has sparked a lively discussion in terms of some possible improvements. Actually, the questions it raised for discussion were not so easy. I see one contributor attempted a specific improved picture, and it has drawn as much fire as the original opus.

I want to give the artist some license on the size and ascension/declination of the sister planets ... we could view it as a schematic of the system in that sense. How fun would it be to have just shown 2 dim dots? But I welcome the education from those here discussing some facts of how they must actually be. I see some comments, but I'm not sure how reliable they are. This would take us back to the data that gives detailed information about the orbits insofar as TRAPPIST, or others, have measured them. Again, that just proves that this rendering is a great springboard for discussion and education. I'm wondering how the TRAPPIST-1 system fits with a Titius-Bode rule. It may, or may not. The orbit of 1d seems not to be well determined, yet. Still, the sizes shown in the sky seem possible to me. It should look like a couple of Earths near a Jupiter, right? (https://www.geol.umd.edu/~jmerck/geol21 ... s/04a.html)

by **neufer** » Sat May 07, 2016 10:24 pm

Boomer12k wrote:
So, they have MONKS there???

https://en.wikipedia.org/wiki/TRAPPIST wrote:
<<The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) is a Belgian optic robotic telescope, which came online in 2010. It is named in homage to the Trappist Order in the Belgian region.

The 48th chapter of the Rule of St. Benedict states "for then are they monks in truth, if they live by the work of their hands". Following this rule, most Trappist monasteries produce goods that are sold to provide income for the monastery. The goods produced range from cheese, bread and other foodstuffs to clothing and coffins, though they are most famous for their beers, which are unique within the beer world, and are lauded for their high quality and flavour. Monasteries in Belgium and the Netherlands, such as Orval Abbey and Westvleteren Abbey, brew beer both for the monks and for sale to the general public. Trappist beers contain residual sugars and living yeast, and, unlike conventional beers, will improve with age. Westvleteren 12 is often considered to be the single best beer in the world.>>

by **Boomer12k** » Sat May 07, 2016 10:04 pm

So, they have MONKS there???

:---[===] *

by **Boomer12k** » Sat May 07, 2016 10:02 pm

I hate losing my keys.... he should have used a FLASHLIGHT....duh...

Interesting to learn about these planets...

:---[===] *

by **geckzilla** » Sat May 07, 2016 8:23 pm

Given the parameters of planet d (and presuming we are on planet d) the sky and the brightness of the star can be quite variable. The star would appear in the sky anywhere between 2.76° to .42° in angular diameter. We wouldn't see a large orb in the sky as depicted, at least not without a telephoto lens. With a narrow field of view there could be stars visible or there might not be, with or without a substantial atmosphere.

You could do a few different things with the illustration and still be within the realm of plausibility, but certainly planets b and c would not look as they do. The one on the right might look like a ring (think Titan) if it had a thick, extended atmosphere. It most definitely would not look like a crescent. If it was on the other side of the star it would be a very faint, barely visible, fully illuminated disc. There is no way for it to be a crescent.

by **Chris Peterson** » Sat May 07, 2016 7:52 pm

neufer wrote:
Chris Peterson wrote:
Steven Dutch wrote: You would not see stars in the sky, especially close to the sun.
I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.
The star overall radiation is indeed ~1900 times dimmer than the Sun but this is cancelled out by the planet being ~43 times closer (such that the planet receives about the same overall warming radiation as the Earth). However, most of this is infrared radiation and the visual luminosity is ~270,000 times dimmer than the Sun which from the close planet is only 0.7% as bright as the Sun. In any event, the main factor is that the atmosphere is assumed to be very thin except for wind blown particles.

That's a good point about the distance. Still, given a visual luminosity on the order of 1% that of the Sun, we'd expect the daytime limiting magnitude- given an Earth-like atmosphere- to be around mag 3, which means there would be about 200 stars visible in the sky, say 50-100 in a given hemisphere, depending on conditions. Of course, more would be visible if the atmosphere were thinner than Earth's, and not overly dusty.

by **neufer** » Sat May 07, 2016 7:36 pm

Chris Peterson wrote:
Steven Dutch wrote:
You would not see stars in the sky, especially close to the sun.
I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.

The star overall radiation is indeed ~1900 times dimmer than the Sun but this is cancelled out by the planet being ~43 times closer (such that the planet receives about the same overall warming radiation as the Earth). However, most of this is infrared radiation and the visual luminosity is ~270,000 times dimmer than the Sun which from the close planet is only 0.7% as bright as the Sun. In any event, the main factor is that the atmosphere is assumed to be very thin except for wind blown particles.

by **Chris Peterson** » Sat May 07, 2016 3:44 pm

Steven Dutch wrote:You would not see stars in the sky, especially close to the sun.

I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.

by **Steven Dutch** » Sat May 07, 2016 3:26 pm

You would not see stars in the sky, especially close to the sun. Also, if the star is emitting enough light to keep the planets warm, it wouldn't appear red. It would saturate your retina and look white. Possibly the sky or shadows might have a reddish cast. Anyway, "red" stars are more pinkish orange than red. Finally, if the planets were close enough to have easily visible disks, especially orbiting a star with small mass, they'd destabilize each others' orbits.

by **Chris Peterson** » Sat May 07, 2016 3:21 pm

Ann wrote:
Chris Peterson wrote:
rstevenson wrote: I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.
Not just as bright, but also as white.
I wasn't talking about denizens of those worlds. I was talking about us. Would the daytime sky on a planet orbiting TRAPPIST-1 be as bright and as white (make that blue) to us as the Earth sky is?

Yes, I know that's what you were talking about. But Rob was, and I was simply expanding on his comments.

Visually, I think we'd see the star as less red than it appears in the illustration- probably a warm white, the same way we see these kinds of stars when we view them in our sky. What color the sky would look is harder to judge. I think we'd see some reddish scatter near the star, but in other parts of the sky it's perfectly possible we'd see blue, but the sky would be much darker than on Earth because there would be much less scatter. Seeing stars in the daytime seems all but certain. The light on the landscape (especially snow) would look reddish at first, but our natural white balance system would probably desaturate that considerably after a few minutes.

I know that our eyes are extremely good at adapting to different kinds of ambient light, but for myself, there is just no way I can believe that I would mistake the sky of a TRAPPIST-1 planet for our own clear sky.

I agree.

There is no way I can believe I would find their skies as bright as our own clear daytime sky, or that I would in any way mistake the color of their skies for our own.

Color, certainly. Brightness is much more complex, because of the way we accommodate.

by **Ann** » Sat May 07, 2016 3:13 pm

neufer wrote:
Ann wrote:
the light from this small cool sun would be almost exclusively red, orange and yellow. Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.
When blue & green light is scarce
red, orange & yellow light scatter quite well in an Earth-like atmosphere:

http://apod.nasa.gov/apod/ap150908.html

Yes, we all know that the sunset and sunrise skies of the Earth can be quite red. But that color soon disappears as the revolving of the Earth makes the Sun appear to rise higher, or sink deeper below the horizon.

Earth skies can also be quite red if the air is strongly polluted. But I am talking about the color of the clear daytime and relatively unpolluted Earth sky.

Ann

by **Ann** » Sat May 07, 2016 2:57 pm

Chris Peterson wrote:
rstevenson wrote:
Ann wrote:... Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.
I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.
Not just as bright, but also as white.

I wasn't talking about denizens of those worlds. I was talking about us. Would the daytime sky on a planet orbiting TRAPPIST-1 be as bright and as white (make that blue) to us as the Earth sky is?

I know that our eyes are extremely good at adapting to different kinds of ambient light, but for myself, there is just no way I can believe that I would mistake the sky of a TRAPPIST-1 planet for our own clear sky. There is no way I can believe I would find their skies as bright as our own clear daytime sky, or that I would in any way mistake the color of their skies for our own.

I realize that the brightness of their skies has at least something to do with how closely the planet is orbiting the faint orange sun. But even so... no, their skies would not be as bright as the Earth's daytime blue sky and not the same color. At all.

Yes, I realize that I would have to have some "absolute comparison" in order to be sure that their skies and daylight was really truly different from our own. So imagine I could bring this boy with me to the TRAPPIST-1 world. If his relatively dark orange shorts and dark orange breast pocket looked brighter than his light blue shirt, I would know that I was on a planet whose daylight was different from our own.

Ann

by **Chris Peterson** » Sat May 07, 2016 2:42 pm

rstevenson wrote:
Ann wrote:... Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.
I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.

Not just as bright, but also as white.

by **neufer** » Sat May 07, 2016 1:39 pm

Donald Brandshaft wrote:
It is frequently stated that worlds so close to their sun must be tidally locked so that only one side faces the sun. However, Mercury has a day every (Mercury) years. These worlds have years measured in days.

You left out the "2" : Mercury has a day every 2 (Mercury) years.

These tidally locked worlds have no "days" in the normal sense.

by **neufer** » Sat May 07, 2016 1:27 pm

Ann wrote:
the light from this small cool sun would be almost exclusively red, orange and yellow. Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

When blue & green light is scarce
red, orange & yellow light scatter quite well in an Earth-like atmosphere:

http://apod.nasa.gov/apod/ap150908.html

Nevertheless... the red skies here are most likely due to wind blown ice crystals.

https://en.wikipedia.org/wiki/TRAPPIST-1 wrote:
<<It is important to note that tidally locked planets likely have very large differences in temperature between their permanently lit daysides and their permanently dark nightsides, which could produce very strong winds circling the planets while making the best places for life close to the mild twilight regions between the 2 sides.>>

by **bystander** » Sat May 07, 2016 1:21 pm

viewtopic.php?t=35891

by **JohnD** » Sat May 07, 2016 1:04 pm

I was going to ask that APOD didn't use these 'artist's impressions', except when they were to illustrate a point, but oldrcd has done so, more forcefully!

The scene in the sky may or may not be accurate, but the foreground is mere speculation. Fine for a cover of an SF book, preferably with the addition of an alien spaceship, but this is a science truth website.

John, In Puritan mode

Starship Asterisk*

APOD: Three Worlds for TRAPPIST-1 (2016 May 07)

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