Comments on: BAFact math: How bright is the Sun from Pluto?

By: Thornton

Thornton — Tue, 21 Aug 2012 02:24:36 +0000

Correction…. 100 million… from Pluto, Alpha Centauri is about 100 million times dimmer than our sun is from Pluto…not 100 billion. Still, our sun is 100 million times brighter. It would hurt to look directly at the sun from Pluto…

By: Thornton

Thornton — Tue, 21 Aug 2012 01:55:00 +0000

All this is not surprising… even the closest stars are so, so, so, so much further out than Pluto. Since Alpa Centari is about 10,000 times further than our sun is from Pluto… Alpha Centari is slightly brighter than our sun, but from Pluto, (or Earth) Alpha Centari is about 100 billion times more dim than our sun is from Pluto…
Our sun would produce about 7 lumens per square foot on the surface of Pluto, which favors most Police or Sure Fire flash lights shining on the ground from 5 feet high…. Looking at the sun from Pluto would be akin to looking at an orange-yellow Arc welder.. from 30 or 40 feet…. it would leave a spot in your eyes when you closed you eye lids… Like the filiment of a bright HID light…. DON”T believe the old saying that from Pluto the sun only looks like a bright star ! WRONG. Pluto is very, very, very, very close to our sun compared to the nearest star (excluding our sun, of course, which is similar to Alpha Centauri).

By: Matt B.

Matt B. — Tue, 24 Apr 2012 16:27:26 +0000

@48 Treczoks:

Even though the Sun is being describe as looking like a point here, for a solar eclipse to occur, the shadowing object must appear at least as big as the Sun from the location of the world where the eclipse is seen. Since the Earth is 1/100 the size of the Sun, an Earth-sized object would have to be no more than 1/100 as far from Pluto as the Sun to cause a lunar eclipse on Pluto, which would be < .39 AU from Pluto. Since asteroids are tiny compared to Earth, they would have to be even closer to Pluto. So asteroids in the main belt absolutely would not be able to eclipse the Sun from Pluto's perspective.

By: Melf_Himself

Melf_Himself — Sat, 17 Mar 2012 09:08:38 +0000

Phil, you’re going to need to extend your calculations a little here. Brightness scales with log luminance. e.g. twice as many photons does not give twice the brightess.

By: Dave Jerrard

Dave Jerrard — Fri, 16 Mar 2012 18:03:26 +0000

@41. Lawrence D’Oliveiro

Several years ago, it was more of an issue, where even a airplane 2km above the origin would start to quantize, but the software has become more accurate since. With planets, at least out to Mars in my case, quantization errors are negligible at the planetary scales, though small objects like asteroids will be obviously butchered.

I used an old technique where I move the world – in this case, the solar system – so the camera and smaller objects are always near the origin, but even with this scene, I’m still running into precision limits. I guess the next option is to separate all the planets from the solar system parent, and move them all separately. This will get rid of the huge offsets they’re currently using, but will probably also mean another day of tweaking the camera motion to avoid the huge overshooting problem due to moving across such vast distances.

Other than the smaller objects quantizing, the scene is actually working far better than I had expected.

@49. Nigel Depledge

You don’t know me too well, do you?

@56. Jasonium

Saturn would be slightly larger than 1/9th the size of the sun as seen from Pluto. I just checked this in Starry Night, going back to the year 747AD, which is the most recent year the two planets were that close.

In April, 2956BC, Pluto and Neptune were about as close as they’ll ever get, and Neptune would appear about a little larger than 1/3 the size of the sun, which would look a bit smaller than it did in 747 AD.

If you want to have some fun & kill a lot of time, grab a copy of Celestia – it’s free – and you can see how the solar system looks from pretty much any place & any time.

By: Anthony

Anthony — Fri, 16 Mar 2012 17:42:31 +0000

@Livia West: arbitrarily little; skyglow would be 1/900 to 1/2,300 as much as on Earth, but that’s still visible (you can see skyglow from the full moon). The question is whether you could actually tell that it was blue, I’m guessing you could (you could probably tell it was blue under the same light level that you could tell an object painted blue was blue, and sunlight on Pluto would be 10-100 lux depending on distance and time of day, which is comparable to dim internal lighting and is adequate for poor color perception).

By: Dangerous Intersection » How bright would the sun look from Pluto?

Dangerous Intersection » How bright would the sun look from Pluto? — Fri, 16 Mar 2012 16:58:08 +0000

[...] Bad Astronomy discusses how bright the sun would look if you were standing on the almost-planet Pluto. Related posts:What’s it means to be a “Bright”? [...]

By: Jasonium

Jasonium — Fri, 16 Mar 2012 16:43:03 +0000

At closest approach, would Saturn appear larger than the Sun on Pluto? Would Neptune appear larger?

By: Doug

Doug — Fri, 16 Mar 2012 15:41:01 +0000

Heinlein was an engineer. But he knew enough physics to be dangerous and was known to consult with physicists. So he usually got it right.

I dunno Phil. The name of this feature is very close to BARFact. That’s how I read it at first glance . . .

By: Livia West

Livia West — Fri, 16 Mar 2012 14:39:01 +0000

How much light is necessary to make the sky glow, and would it, if the Earth were in Pluto’s orbit?