Parker is at 0.04 AU, Mercury is 0.21 AU.

Or in more imaginable terms: 9 solar radii out at the closest passes in the far future. Here's an older sim clip showing the process, https://www.youtube.com/watch?v=IClNiZ2-ee4

I have no clue how large the sun is, for all I know it could be 0.000001AU or 0.01AU, but I do know how hot the sun can be at 1AU and that Mercury is scorched at 0.21AU so that's a lot more imaginable than a multiple of some unknown unit, particularly "in the far future" (sounds to me like 10k years, but given the topic of a single mission, maybe it's 30 years? Or 10? This is super vague, too.)

Yes, that's the kind of thinking that resonates with me as an astronomer, and when I talk to the general public and non-astronomer scientists, I find that a lot more people have a grasp of how hot it is at 1/5 of Mercury's orbit than 9X the radius of the Sun.

My understanding is that AU is measured from the center of the sun / object. Google tells me that the radius of the sun is ~0.0046AU (1/215th of an AU).

Many people can imagine 0.04 AU and 0.21 AU just fine.

One's 1/5 the distance from the Earth to the Sun, the other is 1/5 that distance.

The distance ladder is a good way to think about it.

The folksy comparison in the article is misleading, or just wrong. The probe is going closer than they imply.

> If Earth was at one end of a yard-stick and the Sun on the other, Parker Solar Probe will make it to within four inches of the solar surface

Perhaps they meant 4 cm.

This stuff with yardsticks, inches,and Fahrenheit is annoying.

Think of it this way. If the distance to earth is a furlong, then its just shy of a couple of rods.

Cubits it is then!

On a side note I always thought AUs were a bit silly and self centered....

IMO light-seconds is actually a really nice unit for interplanetary distances. 1AU ~= 500ls. Not only is the scale nice for human arithmetic, but it serves a dual purpose of also telling you the light delay.

Lightnanoseconds are a useful measure in everyday life as well. A lightnanosecond is about 30cm, or 1 foot.

https://www.youtube.com/watch?v=1-vcErOPofQ&feature=youtu.be...

Oh man that is nice.

I'm pretty interested in this kind of thing but I couldn't tell you to within an order of magnitude Earth's distance from the Sun in metres or miles. I could work it out - it's about 6 light minutes and light travels 300,000 km/s - but I wouldn't expect everyone to do that. So expressing the distance in AU is relatable to me. Looking from the probe at perihelion, the sun will appear 25 times wider, or 625 times larger, than it does from Earth.

And does the fact that AU comes from the earth's distance to the sun make it self-centred? Sure, but everyone we need to communicate with would equally find it centred on them. Compared to other measures like "the distance from the king of England's nose to the tip of his outstretched finger" it's quite neutral.

It's also resulted in the loss of several rockets and probes.

Yes: the closest it will come is 0.04 AU:

https://en.wikipedia.org/wiki/Parker_Solar_Probe

If one AU is 1 meter, 0.04 AU is 4 cm. So it's, roughly, if 3 feet is between the Earth and the Sun, the probe would pass by the Sun at one and half inch.

(It is obviously easier to think in metric units.)

Guessing they calculated it to 1m and 4cm and then messed up the units.

1 yard ~= 1 meter. what's 3 inches between friends? giggity?

Thanks, that makes a lot more sense.

As best I can tell, it's about 10 times closer than Mercury.