Slow adaptation to low magnitude

[Imy]

Does exist a mode in Celestia which automatically simulates the slow adaptation (as the human eyes) to low magnitudes?

For Instance, we must wait to see all milky way with our own eyes ; a telescope needs to catch light a long time in the same celestia area to get nebulaes, needn't it?

Thanks in advance.

[t00fri]

Does exist a mode in Celestia which automatically simulates the slow adaptation (as the human eyes) to low magnitudes?

For Instance, we must wait to see all milky way with our own eyes ; a telescope needs to catch light a long time in the same celestia area to get nebulaes, needn't it?

Thanks in advance.

You should switch on automag mode (CTRL+Y). That simulates telescope enhancement when you decrease the field of view (SHIFT+mouse_left movements!)

Bye Fridger

[selden]

By itself, Celestia immediately sets the brightness of stars and deep space objects using limiting magnitude and (for galaxies) intensity magnification values that the user has selected using the [] and () keys.

A .CEL or .CELX script could be used to generate a sequence of these commands to cause a slow change in brightness similar to what you describe.

[Imy]

How to make this script, please?

[selden]

You'll need to learn the .CEL and/or .CELX (Lua) programming languages. Please read the FAQ that's at the top of the Celestia Scripting Forum.

Here's a trivial .CEL script to change the brightness of stars while looking from the Earth toward the Moon. (So this script can work only two weeks out of a month.) You can, of course, step in smaller increments of magnitude and shorter intervals of time so that the brightness changes more smoothly.

Code: Select all

{

select { object "Sol/Earth"  }
goto {time 0.01}
wait { duration 0.02}

select { object "Sol/Earth/Moon" }
center {time 0.01}
wait { duration 0.02}

setvisibilitylimit { magnitude 6}

print { text " change visibility threshold, \n Starting at magnitude 6 " origin "center"

duration 2}

wait {duration 3}

setvisibilitylimit { magnitude 7}
wait {duration 1}
setvisibilitylimit { magnitude 8}
wait {duration 1}
setvisibilitylimit { magnitude 9}
wait {duration 1}

print { text "  magnitude  9 " origin "center" duration 2}
wait {duration 2}

setvisibilitylimit { magnitude 10}
wait {duration 1}
setvisibilitylimit { magnitude 11}
wait {duration 1}
setvisibilitylimit { magnitude 12}
wait {duration 1}
setvisibilitylimit { magnitude 13}
wait {duration 1}
setvisibilitylimit { magnitude 14}
wait {duration 1}

print { text "  magnitude  14 " origin "center" duration 2}
wait {duration 2}

setvisibilitylimit { magnitude 14}
wait {duration 1}
setvisibilitylimit { magnitude 13}
wait {duration 1}
setvisibilitylimit { magnitude 12}
wait {duration 1}
setvisibilitylimit { magnitude 11}
wait {duration 1}
setvisibilitylimit { magnitude 10}
wait {duration 1}
setvisibilitylimit { magnitude 9}
wait {duration 1}
setvisibilitylimit { magnitude 8}
wait {duration 1}
setvisibilitylimit { magnitude 7}
wait {duration 1}
setvisibilitylimit { magnitude 6}
wait {duration 1}

print { text "  magnitude  6 \n Done. " origin "center"  duration 2}


}


[Imy]

Thanks a lot Selden for this interesting example!

I wonder what can happen if during the magnitude is increasing, i'm changing view direction. In Celestia with this script, nothing changes, but in reality what happens?

Can't this be interesting to decrease CPU use or to increase star number without a big computer to show them when you move (also to show nebulaes..)?

[selden]

View direction and brightness do not affect one another. Brightness applies to all stars and galaxies simultaneously. If you change the direction you look while the script is running, you'll see different stars changing their brightness. I chose to make it look toward the Moon so that the sky would be dark and you could see the effect.

When more background objects (like stars) are visible, Celestia does have to do more work to test which are being blocked by foreground objects.

You don't have to use a script to change how many stars are visible. Type a [ or a ] several times to get the brightness level you want. Celestia will remember the magnitude limit when it exits and will use it the next time it starts.

[Imy]

How can i use in a script, a variable that I will slowly increase (0.1 to 0.1)from a magnitude threshold to the default current magnitude defined in Celestia (Also How to get it?)?

When you want to see nebulae (in reality) you must use telescope and keep it in the same direction a long time to get very little light of them, mustn't you? Adding the little light, you can get up little magnitude object?

When you use Celestia educationnal objects (particulary nebulae), you can load Celestia with nebulae (which make more realistic than in celestia basic package according to me), but it's very slow for my computer. This dynamic loading that dynamic magnitude script allows will be interesting to decrease the time when i move.
...I even think that a kind this stuff would be useful in the basic package...?

[t00fri]

When you want to see nebulae (in reality) you must use telescope and keep it in the same direction a long time to get very little light of them, mustn't you? Adding the little light, you can get up little magnitude object?

That is not generally true! The human eye does NOT accumulate light unlike CCD's or film. Film also does this only during a limited time (due to the well-known Schwarzschild reciprocity failure). What astronomers use to optimize the eyes sensitivity is so-called "averted vision".

So you must specify what /receptor/ medium you are imagining.

The human eye will need a certain dark adaptation time in general, but that's physically a completely different issue.

Also, when realistically simulating a telescope, one must carefully distinguish the light amplification of /pointlike/ and /extended/ objects. The dependence on telescope parameters (diameter, focal length, ...) is totally different in these two cases. What is also a crucial input is the background sky illumination. That has entirely different effects when observing from Earth or from Space.

So the best is to first learn a bit about these elementary physics/astronomy issues before starting to write scripts.

Bye Fridger

[Imy]

You're right, I'm confusing receptor behaviors, i'm confusing between pupil dilation and CCD adding system...
It's probably because of the similar result : you must wait to see objects according to their own magnitude.
The Selden's script is a good example for simulating Human's eyes adaptation. Indeed, in this case, changing direction doesn't change magnitude.
What i have in mind? Well, i believe that all objects are not useful to navigate through the system solar. I have in mind the idea to reduce the cpu use of my computer. But these objects will be however welcome slowly appearing automatically (like human vision) when you are no moving (to get a painting view...)