[benjoffe]

> Is the 'light' reflecting off the asteroid emitted from the sun? I had never seen or even knew radar could distinguish value like what is shown here.

Yes it's emitted from the sun, it's clear given that the time-lapse shows "Inner moon eclipsed" when passing behind the site of the asteroid that is not lit.

[Lordsandwhich]

I was always under the assumption that with Radar images that it didn't rely on a light source as technically the radar is the source. So that the impression that there is a light an dark side was based purely on the motion towards and away from the receiver.

But, you have pointed out something interesting and that would appear to indicate other wise. The clear rotation independent of source already shows that I am wrong on that.

Apparently I don't understand this very well.

[RachelF]

You are correct, the "light" is the transmitted radar pulse from Goldstone, not from the sun.

They do all sorts of fancy signal processing to get this sort of resolution.

Because radar power received goes down with 1/(distance^4), the inverse square law, squared, this is hard to do at astronomical distances.

The power level differential between transmitted and received power can be in the order of ~10^15.

Goldstone transmits a 500kW radio pulse but will probably get nanowatts back, which is amplified millions of times by the big dish, amplifiers and signal processing.

[radicalbyte]

This thread is very confused.

There are two things: the radar images are created with radio waves emitted by the radar installation. The second thing is that the visualisation shows a light source. They are unrelated to each other. I assume that the light source was added during rendering of the film and that it approximates the sun.

[TorKlingberg]

I don't think the visualisation shows any light source. The radar reflection from the asteroid just looks like it is "lit up"

[ceejayoz]

The radar is the light source, just like shining a flashlight during the night at something.

The actual solar illumination of the asteroid at the time was likely significantly different from what we see in these images.

[Teever]

I don't understand how the phrase 'inner moon eclipsed' tells the reader that the source of radiation for this radar measurement is the sun.

[jaquers]

I don't either :) but sort of a silly question I guess. I presumed it was the sun due to the angle of illumination as well as common sense that the sun is probably the brightest object in the solar system along multiple bands of light; I was really just amazed at the relatively large amount of detail in the image.

[devrandomguy]

Well, if the illumination was from the radio telescope, then the moon would be hidden behind the parent asteroid when it is eclipsed. We would not see it go dark, it would just be obscured.

[azernik]

That's just an artifact of the visualization; the point of view is above the north pole of Florence, which points decidedly away from Earth (probably +/- a few degrees from normal to the plane of the ecliptic).