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Comment by spartanatreyu | Hacker News Reader

You might be interested in this video which talks about using the Earth's gravity to create a telescope with a lens roughly the size of the Earth (a terrascope): https://www.youtube.com/watch?v=jgOTZe07eHA

They also have a follow up video about using Jupiter to create a jovoscope and there's also more about creating a telescope using the sun (although since the sensor would need to be so far away from the Sun, we would essentially need to launch a different spaceship for each target that we tried to image).

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> They also have a follow up video about using Jupiter to create a jovoscope

Just for fun, if you wanted to form the word from Greek roots instead of mixing Latin into it, it'd be "dioscope".

If you stick with the Latin, it's ambiguous whether the combining vowel should be -i-, agreeing with the Latin root ("joviscope") or -o-, agreeing with the Greek root ("jovoscope").

(And for completeness, if you wanted to do it entirely in Latin, the word would probably be "jovivide", but it is generally Not Done to form verbal compounds like that in Latin, unless the verb you're using is either ferre or gerere [both meaning "carry"].)

Entirely in Latin, "videre" would not be the right corespondent verb for "scope" (from Greek "skopos"), but "spectare" (source of English "spectator"), so one could say in Latin "jovispectum" in the neuter gender (something that looks at Jupiter) or "jovispectus" in the masculine gender, though the latter would be more appropriate for the human who uses the instrument, not for the instrument.

An example of a real Latin word formed in the same way is "circumspectus" (someone who looks around) => English "circumspect", so one could say in English "jovispect".

Word compounds from a noun stem with the last vowel changed to "i" + a verbal stem + the thematic vowel, in either the masculine or the feminine gender, are numerous in Latin and formed from many verbs, not only from "ferre" and "gerere".

For example there are many animal names, e.g. sanguisuga (blood-sucker = leech), caprimulgus (goat-milker = nightjar), ossifraga (bone-breaker = bearded vulture), vipera (alive-baby-birth-giver = viper) and others. There are also some insulting names formed in this way in Latin, but those are NSFW, so you may try to guess them, as they also correspond in English to the pattern *-*er, like "blood-sucker".

> vipera (alive-baby-birth-giver = viper)

This one seems like a stretch?

I'm also curious why you interpret the formation as "noun stem with final vowel changed to i", as opposed to "noun stem followed by epenthetic i".

The word "viipera" (long "i") was contracted from "vivipara" (Latin "v" was pronounced like English "w", which favorised the contraction of sequences like "wiwi" into "wii", in a few words), with also the regular change of the unaccented "a" into "e", which happened in all the older Latin words. "Vivipara" is the feminine form of the Latin word that is the source of English "viviparous".

The vipers are unusual between snakes by giving birth to live young, instead of laying eggs, like most snakes.

Both "noun stem with final vowel changed to i" and "noun stem followed by epenthetic i" have happened.

The former to the stems ending in "a" or "o", the latter to the stems ending in a consonant. An alternative interpretation would be that for the stems ending in a vowel the final vowel was removed and an epenthetic "i" has been added, but this is a more artificial interpretation, because there was never an intermediate stage having an "o" stem or "a" stem without the final vowel.

There also exists one case of an older compound word where the initial noun was a stem ending in "i", but the final "i" has been dropped, and the verb remained as a bare root, without forming a stem by the addition of a vowel: "avspec-", which means bird-watcher (with the nominative written as "avspex", i.e. "auspex" in the modern spelling, the source of English "auspices"), from "avi-" = bird and "specere", the non-frequentative form of "spectare". Another example of an old compound word with no epenthetic "i" and with only the bare root of the verb is "juudic-" = judge (justice-sayer, from "juus" and "dicere"). With the exception of a few inherited old compound words like these, all the compound noun+verb words coined more recently used an "i" ending for the noun and a verb stem terminated in the vowel corresponding to the gender.

While you were partially right that the compounds with "ferre" and "gerere" are the most numerous, for the obvious reason that one can form such a compound word for any object that can be carried, there are a large number of Latin words made from nouns with other verbs.

>Earth's gravity

*Earth’s atmosphere

This got downvoted but it is correct. The "terrascope" concept depends on atmospheric rather than gravitational lensing. The deflection through the Earth's atmosphere is about 1 degree, which is orders of magnitude more than you get from the Earth's gravity.

Using Earth as a gravitational lens would give you a focal point about 15000 AU (a quarter of a light year) away, far outside the solar system. But with atmospheric diffraction, you can get a focal point within the Earth–Moon system.

I’m assuming the lazy downvoters had watched the recent PBS SpaceTime episode that talked about the gravitational lens approach in the context of exoplanet imaging, and just assumed that anything involving earth for lensing was gravity based.

That’s a rookie telescope. Let’s use the sun!

https://youtu.be/4d0EGIt1SPc

Cool topic, but completely unacceptable to rant 20 minutes on tangentially related topics before getting to the actual issue at hand. I understand that Youtube prefers longer videos for monetization, but this is absurd.

This is the most entitled comment I've seen all week.

The video has a clickable chapter list and a time scrubber, and the other chapters are closely related.

That still doesn’t disprove the point though. I like videos that get straight to the topic of the title rather than blabbering.

It’s very frustrating to see deceiving titles and the actual content related to the title is 2% of the entire video..

IMHO, the title is not deceiving. As of right now it's "Turning Earth Into a Telescope", and he talks about just this from a historic standpoint.

If you were hoping for the technicalities of it, then I can see how it's not what you want. I know what I think is enough about the history of telescopes, so I skipped that part, but I thought the history behind how he came up with the idea fits squarely into the title.

“Guide to replacing a toilet float valve” doesn’t need to include the history of plumbing.

No one is clicking a video called "turning the earth into a telescope" to actually "turn the earth into a telescope". They are likely doing it for educational or entertainment purposes.

On the other hand almost everyone clicking a video called "Guide to replacing a toilet float valve" is actually looking to replace a toilet float valve.

Sounds like you have identified an underserved market niche. I look forward to viewing your videos.

"To replace a toilet float valve, we must first start with the big bang..."

I sure look forward to watching "Guide to turn Earth Into a Telescope". I'd expect it to be be a different video.

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