# Kerbal Astronomy 101

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You should fix your HTTPS certificate though. It's generally better to encrypt by default, and valid certificates are free (through StartSSL, soon through Let's Encrypt).

I'll look into that. Thankyou.

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• 1 year later...

How did you calculate the apparent magnitude?

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On ‎4‎/‎21‎/‎2017 at 4:15 PM, Alphard said:

How did you calculate the apparent magnitude?

I first computed the apparent brightness of each body.  This was done by taking the luminosity of the sun, expanding its light out into space, and computing how much energy touched the disc of the planet.  I then multiplied that amount by the planet's albedo to determine the amount reflected.  I then let the reflected light expand out into space and determined how much energy per square meter was received back at Kerbin.  I then compared this apparent brightness to the apparent brightness of real life celestial bodies for which I knew their real life magnitudes.  Knowing the relative brightness of two bodies and the magnitude of one body, the magnitude of the other can be computed from the equation,

m2 - m1 = 2.5 * log10 (b1 / b2)

For example, suppose I determine that body #1 is half as bright as Jupiter when Jupiter's magnitude is -2.6.  We have,

-2.6 - m1 = 2.5 * log10 (0.5 / 1)

m1 = -1.85

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10 hours ago, OhioBob said:

I then multiplied that amount by the planet's albedo to determine the amount reflected.

I'm assuming that you took the albedo from the real-life counterparts, right?

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1 hour ago, Alphard said:

I'm assuming that you took the albedo from the real-life counterparts, right?

Squad already assigned an albedo to each body, so I just used their numbers.  However, the numbers they used look to be based on real-life counterparts.

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I am happy to see this thread has popped up again, and auspiciously upon a day when I chanced to stop in again.

(fwiw, the 'community coffee-table project' idea was not bad...  )

@OhioBob, have you chanced to give consideration to expanding this to the Outer Planets Mod yet?  It moves Eeloo (as you likely know by now), so it would involve editing, not just adding on to this existing work (alas).

Edited by GarrisonChisholm
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1 hour ago, GarrisonChisholm said:

@OhioBob, have you chanced to give consideration to expanding this to the Outer Planets Mod yet?  It moves Eeloo (as you likely know by now), so it would involve editing, not just adding on to this existing work (alas).

I started writing something at one time, got distracted, moved on to other things, and never went back to it.  It's still on my todo list, but new things keep getting added that slot in ahead of it.

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Great work. Regarding the mod there is something like that. Research bodies is its name and it does what was said in the OP. You know there are planets and their parameters but everything else is unknown and you have to use a telescope or send a probe to investigate.

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• Tex pinned this topic

I agree, It is Incredibly good work! I wonder if these calculations are still correct for rescaled systems? I play KSP with 6.4 rescale mod, so the distances are 6.4 larger, but all objects also have 6.4 larger sizes, so I guess they are?

` `
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@Walker, as long both the rescale and resize factors are the same, much of what I've written should still hold true.  Obviously things like distance from sun, diameter, orbital period, etc. will change, but things like apparent magnitude, apparent size, temperature, etc. won't change.

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Bellow are some additional images that I created nearly two years ago.  There were made to resemble telescopic views of the planets from a time prior to the advent of space flight (note the intentional blurring and use of black and white.)  I was going to use them in a mock astronomy book, but never got around to it.  Since this thread has had a revival, I figured I might as well share them with you.  Better late than never.

The Sun through a visible light filter.

Moho at gibbous, quarter and crescent phases.

The phases of Eve, viewed over a span of 250 days. When nearly backlit, Eve's atmosphere scatters sunlight to produced a fuzzy halo.

Mun at first quarter.

Minmus at full phase.

Three faces of Duna; photos taken six hours apart shows planet's rotation.

Map of Duna's surface markings, compiled from telescopic observations.

Duna's moon Ike.

Dres (center) at opposition.

Jool at opposition.

Jool with its three large moons. L-R: Laythe, Vall and Tylo.

Photos of Eeloo showing motion against background stars (15 days apart).

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I would pay serious \$ for a coffee table book on the Kerbol system that was published in the approximate faux "1955-ish" era...

I've said great work too much, but; great work Sir.

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On spectroscopy: Couldn't you just point an actual spectrometer at the screen? Or would that not act the same way as an actual star would?

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On ‎5‎/‎11‎/‎2017 at 4:20 PM, cubinator said:

On spectroscopy: Couldn't you just point an actual spectrometer at the screen? Or would that not act the same way as an actual star would?

It would be necessary to sample the actual light from the star.  That would be the only way to observe the spectral lines.

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This kind of stuff should be stock. Start with credible ground based observations, send something to map the planets in order to see them.

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On 5/11/2017 at 10:20 PM, cubinator said:

On spectroscopy: Couldn't you just point an actual spectrometer at the screen? Or would that not act the same way as an actual star would?

It is like a picture of a Lemon on a computer screen. The screen does not emit any "yellow" photons at all (photons with a wavelength between that of red and green in the EM spectrum). Only the real life Lemon emits "real" yellow  (i think a picture on paper also "emits" yellow, due to the CMYK color-space of printer ink)

"Yellow" photons would correspond to a specific signature of some elements on the periodic table, but with our mix of only red/green/blue light from a computer monitor, we would never know if those "yellow" atoms exists(or even infrared/cyan/ultraviolet)

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7 hours ago, Blaarkies said:

It is like a picture of a Lemon on a computer screen. The screen does not emit any "yellow" photons at all (photons with a wavelength between that of red and green in the EM spectrum). Only the real life Lemon emits "real" yellow  (i think a picture on paper also "emits" yellow, due to the CMYK color-space of printer ink)

"Yellow" photons would correspond to a specific signature of some elements on the periodic table, but with our mix of only red/green/blue light from a computer monitor, we would never know if those "yellow" atoms exists(or even infrared/cyan/ultraviolet)

I see now. Thanks for the explanation!

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Holy damn @OhioBob . You put more work into this than I've put into most school projects.

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On ‎5‎/‎15‎/‎2017 at 0:16 AM, Blaarkies said:

It is like a picture of a Lemon on a computer screen. The screen does not emit any "yellow" photons at all (photons with a wavelength between that of red and green in the EM spectrum). Only the real life Lemon emits "real" yellow  (i think a picture on paper also "emits" yellow, due to the CMYK color-space of printer ink)

"Yellow" photons would correspond to a specific signature of some elements on the periodic table, but with our mix of only red/green/blue light from a computer monitor, we would never know if those "yellow" atoms exists(or even infrared/cyan/ultraviolet)

Nice explanation.  It's also important to mention that what's really important when looking at a spectrum are the spectral lines (absorption lines in the case of starlight).  These spectral lines are like fingerprints that reveal the presence of specific elements.  The spectral lines only exist in the original starlight, and are only visible when the light is spread out into its spectrum.  A reproduced image on a computer screen will not have the original spectral lines..  We can produce a spectrum from the original light and then make an image of the spectrum, but we can't make an image and then produce a spectrum from the image that contains the original information.

Edited by OhioBob
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On 4. 5. 2017 at 9:01 PM, OhioBob said:

Bellow are some additional images that I created nearly two years ago.  There were made to resemble telescopic views of the planets from a time prior to the advent of space flight (note the intentional blurring and use of black and white.)  I was going to use them in a mock astronomy book, but never got around to it.  Since this thread has had a revival, I figured I might as well share them with you.  Better late than never.

The Sun through a visible light filter.

Moho at gibbous, quarter and crescent phases.

The phases of Eve, viewed over a span of 250 days. When nearly backlit, Eve's atmosphere scatters sunlight to produced a fuzzy halo.

Mun at first quarter.

Minmus at full phase.

Three faces of Duna; photos taken six hours apart shows planet's rotation.

Map of Duna's surface markings, compiled from telescopic observations.

Duna's moon Ike.

Dres (center) at opposition.

Jool at opposition.

Jool with its three large moons. L-R: Laythe, Vall and Tylo.

Photos of Eeloo showing motion against background stars (15 days apart).

A book would be amazing! If it were to be made, would it be free?

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It might have to be for rights reasons, but I'd find a way to buy Bob a massive steak dinner somehow anyway.

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1 hour ago, Alphard said:

A book would be amazing! If it were to be made, would it be free?

I doubt I'll ever get around to making a book because my priorities are elsewhere at the moment.  I just don't see the motivation to do so returning.  When I did consider making a book, I was planning to simply make it a PDF that could be downloaded for free.  Although a hardcover coffee table book would be terrific, I've never considering absorbing the expense to do such a thing.

Edited by OhioBob
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Also, on mountaintops of small islands like Mauna Kea or La Palma (where some big observatories are located), there can be seeing good enough to resolve a disc with a diameter of only 0.4", using lucky imaging. Also, kerbals may have invented adaptive optics, reducing the seeing limit to nearly zero (it is not so extremely perfect)  The only limiting thing then is the optical resolution, given by a telescopes aperture.

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9 hours ago, Alphard said:

Also, kerbals may have invented adaptive optics...

The presumption is that Kerbal and human technology have developed along a similar timeline.  My article is written assuming a 1950s level of technology.  Adaptive optics didn't become practical until the 1990s.

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• Tex unpinned this topic

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