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Comment by mcorning | Hacker News Reader

For reference 1 AU (Astronomical Unit) is about 150 million km. Saturn ranges from being about 7 to 11 AU away from Earth. Voyager 1 is 152 AU away. This object is excitingly close and will be fun to study.

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Is it possible to get a probe out that far in time to make a good intercept?

I imagine with this (relatively) short notice this is cutting it a bit close to orchestrate a proper orbital insertion by a designed, manufactured and tested program?

Some context: It took Cassini-Huygens 7 years to reach saturn with two venus and one jupiter flyby. It took New Horizons 9 years to reach pluton with jupiter flyby. With Inclination of 95.467° and Argument of perihelion of 326.285° flyby could happen near to Ecliptic but for getting to orbit one would need a nice gravity assist from jupiter.

Maybe this will motivate us to finally design and launch a probe that launches in two or more launches, all but one of which are fuel.

All our normal expectations for probe arrival times and such are based on one-shot launches, straight out of Earth's gravity well into escape velocity in one shot. It's not like launching with fuel suddenly makes it a two-day trip or anything, but it can do quite a bit of shortening and allow for quite a lot more maneuvering.

This is one of the next touchstones in space progress I've been looking for. A lot of previously impractical things become practical if we can routinely do multilaunches.

> Voyager 1 is 152 AU away

Hmmm, can we make 11au?? I think so.

This is not a ridiculous question and does not deserve a mean answer.

Voyager 1 has been flying for over 43 years [0]. In that time it went over 150 AU. This averages about 3.5 AU/year. It took, from start of project to launch, about 5 years (1972 - 1977 [1]).

If this body is going to be 11 AU away in 10 years away we'd need to move at an average 2.2 AU/year and hit the right launch windows.

I think that it falls into the "yes, it's possible" but not into the "of course it's possible, how could you even ask" category.

[0] - https://en.wikipedia.org/wiki/Voyager_1

[1] - https://voyager.jpl.nasa.gov/mission/timeline/#event-voyager...

The question isn’t can we make 11au. That’s facile. Can we make 11au at the exact velocity, location, etc etc etc?

I don't think Saturn comes that close, should be 8 AU at best, given that perihelion is at 9 AU.

https://www.universetoday.com/15311/how-far-is-saturn-from-e...

> For the sake of simplicity, Saturn is 1.2 billion km, roughly 7 AU, from the Earth when the two are at their closest approach to one another. They are 1.67 billion km, around 11 AU, from each other when they are at their most distant. Saturn and Earth are the closest to each other when they are on the same side of the Sun and at similar points in their orbits. The are the most distant when on opposite sides of the Sun.

> Saturn is 1.2 billion km, roughly 7 AU

That's a unit conversion error. 1.2 billion / 150 million is 8, not 7.

I believe the 1.2B km was referencing mean orbital distance from the sun, which would be 8 AU, and therefore 7 AU from earth on closest approach.

No.

Saturn's perihelion (closest distance to the Sun) is 1.35B km (9.0 AU), its aphelion (furthest distance) is 1.51B km (10.1 AU), and its mean distance is 1.43B km (9.6 AU).

Thus, at closest approach Saturn is 8 AU from Earth (since Earth orbits at an almost-constant 1 AU from the Sun).

After checking Wikipedia, you are correct.

Stupid question:

The Hubble photos we have from Saturn are a 7-8 AU range, right?

Even more stupid question:

Pointing the Hubble there is worth the effort? how many pixels wide would be a 200km diameter object at 11 AU?

Unfortunately Hubble has issues at the moment. There's a couple of HN submissions about that.

--> https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...

> how many pixels wide would be a 200km diameter object at 11 AU?

Depends on zoom and resolution of the camera.

So pretty much between Saturn and Uranus....

Even as an adult that still always makes me chuckle. I can't help it.

It’s pronounced your-uh-ness by pretty much everyone (or your-ah-noose if your going by the greek god and not the Latin copy/paste.)

I think "pretty much everyone" is an exaggeration. Google's pronunciations (British and US) are both the 'anus' version -- though the British one has a secondary stress on the first syllable, rather than the schwa of the US version.

Growing up in Australia, the British 'you-ray-nəs' (i.e. not quite 'your anus', but only because of the first vowel sound) is the pronunciation I was familiar with. Lately I've heard 'you-rə-nəs' fairly often, but not exclusively.

in Arabic (and a bunch of other languages I'm sure) it's pronounced: Oranos, I don't understand why the U in Uranus is not pronounced like the U in Ultra.

Cuz in Greek (my mother language), we pronounce "Ουρανός" as "Ouranos".

> ”Our

Good to know, I guess...

A shot in the dark but I think there’s a lot of “ult”s in English but not many “ura”s

Uranium and Urine

In Russian it's simply "Ooran".

> or your-ah-noose if your going by the greek god

I doubt that Οὐρανός is pronounced anywhere close to "your-ah-noose", unless you're pronouncing "your-ah-noose" in a very strange way.

https://www.youtube.com/watch?v=SQTKGXmITZg

This just sounds like "urine us". Potato, potato?

https://www.gocomics.com/getfuzzy/2003/02/18

Leave it to HN to explain grammar, some history and a bit of etymology in response to a childish joke comment.

And, that's why this place is great.

Hope I can contribute, because this is actually very interesting. According to this [1], the most common American pronunciation was closer to "Your anus" (accent on the A in anus) until 1986, when a space probe was flying by and news casters thought weeks of that would get too "giggly", so they deliberately started pronouncing it "Urine us" (accent on the first syllable).

[1] https://www.dollarshaveclub.com/content/story/anus-urine-us-...

Thank you. That was amusing to read and I never actually realized there was so much about the pronunciation, I've heard a few different ones. but I always took it for regional dialect differences not something done intentionally. I may have sounded sarcastic, but I was genuinely serious, I really do enjoy the interesting factoids spawned by sometimes the most innocuous comments on HN. HN really does have a lot of people knowledgeable about a huge range of things.

I prefer to call it the Georgium Sidus!

Nope. I say your-anus.

You might but that is an incorrect pronunciation and the only time I’ve heard that (other than from people who aren’t into astronomy) was in elementary school and even then the teacher told us it was a common, but wrong, pronunciation.

A thread of people discussing pronunciations without saying where they are from or using IPA is a pointless waste of time. You may as well be talking about what time it is by posting “well, it’s dark here!”

Location/accent is important, but sometimes we can get by without IPA. There will be some ambiguity, but often we're sufficiently familiar with each other's accents to interpret phonetic spellings as intended. (Though I do think the ə symbol is indispensable, because representing the schwa sound with 'uh' is just confusing.)

edit: sorry, just realised I probably misread you (as saying we should say where we're from and use IPA), in which case this comment is redundant.

It doesn’t really matter where you’re from. If you pronounce Uranus as your-anus you are pronouncing it wrong.

Your-anus! Ahh! Take that!

That's terrifying, no? A whole planet (yes a dwarf one, but still a PLANET) is just rogue and will wander through the orbit of Sol as it pleases.

It's not a rogue planet, that implies Interstellar. This is an object with a very long orbit that takes it out to he Oort cloud but still - a permanent resident of the solar system.

It's basically just an exceptionally large comet. It's not Melancholia.

Love that movie

It needs a sequel.

It made me so nauseous I had to stagger out of the cinema.

> I would estimate at an albedo of 0.01-0.08 a diameter of 130-370 kilometers (nominally 160) which puts it on a similar scale, if not larger than, Sarabat's huge comet C/1729 P1, and almost undoubtedly the largest Oort Cloud object ever discovered- almost in dwarf planet territory!

So a bit less dramatic but still really cool.

For reference, a nominal 160km diameter would put it around the same size as the 40th largest asteroid known. Huge for an object coming from the oort cloud, but not really huge in comparison to other rocky bodies in the solar system.

How come our culture didn’t base astronomical units around base 10 of our current units?

It's an old unit, so there wasn't a global standard yet, and it's exact value wasn't known for a long time, but it was still useful for ratios. E.g. if you observe the orbit time of another planet, you can tell its distance from the sun relative to the distance of Earth to Sun (1 astronomical unit) relatively accurately, even if you can't measure what it is in meters very well.

For my purposes 10 AU has a lot more meaning than 1 billion km. 1 AU has a lot more context

It's one of those things that I still tilt my head slightly at when thinking about how the human brain struggles with really large numbers. Its just an odd thing.

In a case like this, I suspect it has more to do with visualizing the solar system rather than how large something is. When we speak in AU, we can create a mental model with the Sun, Earth, and other object since everything is normalized to the size of Earth's orbit. When we speak in kilometers, a bit of arithmetic has to be done before creating the model. Regardless of the units though, we aren't directly visualizing the distances since they will be outside the scope of human experience until we actively start traveling the solar system.

Edit: for clarity.

I have more trouble with parsec. I have a rough idea of how big our galaxy is in light years and some idea about nearby stars. Age of the universe helps anchor things in billions of light years. Then suddenly something is measured in parsecs. Probably a similar thing for the experts.

Just because nobody has said it yet and it's often assumed knowledge, one AU is supposed to be roughly the distance from Earth to the sun.

Astronomers could reasonably well measure angles between objects in the night sky, and with some basic geometry, you can measure the relative distances between objects reasonably accurately. For instance, if you have a triangle ABC, and you know the angle ABC is 45 degrees, and the angle ACB is also 45 degrees, you know that the distance AB will be sqrt(2)/2 times the distance BC. If you have dozens of other points you want to know about, you can calculate the distances relative to BC as well. But what if you haven't the foggiest idea how many toises long BC is? (this was well before the metric system; toises was the unit of choice for Cassini) You either give units of toises for, for instance, the size of the Mars orbit with error bars of +/- 80%, or you give the size of the Mars orbit in terms of multiples of BC with error bars of +/- 5%.

Measuring the AU is fraught with errors of all sorts. For centuries it mostly consisted of exploiting tiny parallaxes on the Earth's surface between planetary bodies- for instance, Cassini and Richtie measured the parallax of Mars between Paris and French Guiana. But a small error propagates to a much, much larger error in the final result than relative distances between planetary bodies in AU distances. If your measurement of the parallax of Mars is off by one arcminute, your measurement is totally useless, but if your measurement of the angle to Mars is off by one arcminute, your distance to Mars in AUs is off by a few percent.

It wasn't until the 1960s when the JPL measured distances to Venus and Mars using radar that we were confident we had a good grasp on how long an AU was. But by that point, we had already measured the relative distances between the bodies in the solar system using the AU ruler relatively accurately for centuries.

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