5 ms·

> Have to disagree. You take your pocket tape measure, carefully hook the end of the tape on the Sun and slowly walk to Pluto. You read what it says. That is a

> Have to disagree. You take your pocket tape measure, carefully hook the end of the tape on the Sun and slowly walk to Pluto. You read what it says. That is a distance. By that measure then, you carefully hook your tape measure to Fomalhaut and slowly walk out to the outer ring, whereupon your ancient eyes perceive the distance to be 120 AU, not 240 AU (since 240 AU is the diameter). A given rock in the outer ring is therefore less distant from Fomalhaut than Voyager is from the Sun. That's all the parent is saying, and I agree with them - I, too, know the difference between radius and diameter but a quick read of your comment left me thinking that Fomalhaut's outer ring is orbiting further away from Fomalhaut than Voyager is from the Sun. It's clearer to compare a radius to a radius, is all.

6E696365 3y ago
>It's clearer to compare a radius to a radius, is all. The OP wasn't comparing a diameter to a radius, he was comparing one line to another line: the diameter of the outer ring (line going from one end to the other passing through the middle) and the distance between Pluto and the Sun (line between two points). The fact that Pluto orbits the Sun is just a coincidence for the purposes of this comparison.
- danparsonson 3y ago
  The "Sun-Pluto distance" is colloquially understood as both of those things - a distance in a straight line right now, and the radius of its orbit on average. I think it's far more common for people to assume the latter as I did, but feel free to ask around and find out for yourself. Note that the instantaneous Sun-Pluto distance varies considerably due to the eccentricity of its orbit, and the distance OP quoted is the orbital semi-major axis (what one might refer to as the orbital radius for the sake of brevity), not the present distance. OP was mathematically correct, just a bit unclear. We really don't need to spend so much time on this.

6E696365 3y ago

>It's clearer to compare a radius to a radius, is all. The OP wasn't comparing a diameter to a radius, he was comparing one line to another line: the diameter of the outer ring (line going from one end to the other passing through the middle) and the distance between Pluto and the Sun (line between two points). The fact that Pluto orbits the Sun is just a coincidence for the purposes of this comparison.

danparsonson 3y ago
The "Sun-Pluto distance" is colloquially understood as both of those things - a distance in a straight line right now, and the radius of its orbit on average. I think it's far more common for people to assume the latter as I did, but feel free to ask around and find out for yourself. Note that the instantaneous Sun-Pluto distance varies considerably due to the eccentricity of its orbit, and the distance OP quoted is the orbital semi-major axis (what one might refer to as the orbital radius for the sake of brevity), not the present distance. OP was mathematically correct, just a bit unclear. We really don't need to spend so much time on this.