Learn Hardcore Japanese: kodomo no uti ni utyuu no hon wo yondari, bouenkyou de hosi wo mitari suru to, tenmongaku ni kyoumi wo motu hito ga ooi sou desu. - They say that if you read books about space and look at stars with a telescope while you’re still a child, many people become interested in astronomy.

子供のうちに has a nuance of “while you still have the chance as a child / before you stop being a child.”
子供の時 is more neutral, simply “when (someone) is a child.”

So:

子供のうちに宇宙の本を読んだり…すると…
→ “If (someone) does things like read space books while they are still a child…”

The うちに version often implies that that period is special or limited and that something tends to happen if you do X during that time.

Why is there a の between 子供 and うち? What is 子供のうち as a structure?

Here, うち means “span/period (of something)” or “state of being (something).”

The pattern is:

Noun + の + うち（に） → “while in the period/state of N”

So:

子供のうちに = “while in the period of being a child”

The の works like a possessive or linking particle:

子供のうち = “the time/phase belonging to ‘child’” → “one’s childhood period.”

What does the 〜たり…〜たりする pattern express in 読んだり、望遠鏡で星を見たりする?

The pattern Vた形 + り、Vた形 + りする is used to:

List example actions (not an exhaustive list)
Often suggest variety or repetition of activities

So 読んだり、星を見たりする means:

“do things like read (space books) and look at stars (through a telescope)”
Implicitly: “among other similar activities”

It does not mean you only ever do exactly and only those two things; it’s representative, like saying “such as X and Y” in English.

Why is する there before と? Isn’t する just “to do”?

Yes, する is “to do”, but here it’s the main verb of the たり…たりする pattern:

読んだり、星を見たりする = “to do things like read and look at stars”

Then と attaches to the whole clause:

（子供のうちに）読んだり、星を見たりすると、…

This と is the conditional “if/when”:

“When / If (someone) does things like read space books and look at stars while they’re a child, …”

So すると here is not “do and then…”, but “(if one) does 〜, then…”.

What kind of conditional is 〜すると in this sentence? How is it different from 〜たら or 〜と in other uses?

Here, 〜すると is the conditional と:

V辞書形 + と → “when/if V happens, (then) … happens (as a natural/typical result)”

It often describes general truths, tendencies, or automatic results, not one specific event.

Compare:

読むと、眠くなる。
“When I read, I get sleepy.” (general tendency)

In this sentence:

読んだり、星を見たりすると、天文学に興味を持つ人が多いそうです。
“When people do things like read space books and look at stars, many of them come to be interested in astronomy, I hear.”

〜たら can talk about one-time, specific situations more easily, while と is more generic, automatic-result-like. That fits the idea of “many people tend to…” here.

Why is it 望遠鏡で星を見る instead of 望遠鏡を星を見る?

The particle で here marks the means/instrument used to perform an action:

望遠鏡で星を見る
= “to look at stars with a telescope / using a telescope”

General pattern:

道具 + で + V
= “do V with/by means of that tool”

Using を after 望遠鏡 would make it the direct object, which does not match the meaning “look at stars using the telescope.” The direct object of 見る is 星 here, marked by zero particle (just 星を is implied but often omitted in speech/writing; here it’s explicitly written).

Who is the subject of 読んだり、見たりする and who is the subject of 興味を持つ人? Aren’t we missing subjects?

Japanese often omits subjects when they are clear from context or when the statement is general.

Here:

(人は) 子供のうちに宇宙の本を読んだり、望遠鏡で星を見たりすると、(その) 天文学に興味を持つ人が多いそうです。

A natural interpretation is:

The implied, generic “people” (or “children”) do the activities in the first half:
宇宙の本を読んだり、星を見たりする
Then among those people, there are many people who come to have an interest in astronomy:
天文学に興味を持つ人が多い

So both clauses are about people in general, not a specific “I/you/we.” The sentence describes a general tendency.

Why is it 天文学に興味を持つ and not 天文学が興味を持つ or 天文学の興味を持つ?

The set phrase is:

〜に興味を持つ = “to have an interest in ~”
〜に興味がある = “to be interested in ~”

The thing you’re interested in takes に:

天文学に興味を持つ
“to have an interest in astronomy”

You can’t say 天文学が興味を持つ, because 興味を持つ is what people do; astronomy itself cannot “have interest.”

You also don’t say 天文学の興味を持つ in this sense; that would sound like “to have astronomy’s interest” (as if astronomy is the possessor), which is not the intended meaning.

Why is it 興味を持つ人 and not just 興味を持つ at the end?

興味を持つ人 is a relative clause + noun structure:

興味を持つ = “(they) have interest”
人 = “people”
興味を持つ人 = “people who have interest / people who are interested”

Japanese often turns a verb phrase into a description of a noun:

英語を話す人 = “people who speak English”
音楽が好きな人 = “people who like music”
天文学に興味を持つ人 = “people who are interested in astronomy”

You need 人 because the sentence is saying “there are many people who…”, not just “there is a lot of interest.”

What exactly does 〜そうです express here? Is it “I hear that…” or “It looks like…”?

In this sentence, 〜そうです is the hearsay / reported information そう:

Form: [plain form] + そうだ / そうです
Meaning: “I hear that… / It is said that…”

So:

天文学に興味を持つ人が多いそうです。
= “I hear that there are many people who come to be interested in astronomy.”
or “Apparently, many people become interested in astronomy.”

This is not the “seems/looks” そう that attaches directly to stems, like:

おいしそう = “looks tasty”

Here, 多い is in plain form 多い + そうです → “I hear (that it is) many.” It’s reporting what the speaker has heard or read, not what they are visually judging.

Why use 多い in 人が多い instead of 人がたくさんいる? Is there a difference?

Both are possible, but they have slightly different feels:

人が多い
- More compact, often sounds a bit more formal / written
- Often used in statements of tendency, statistics, general facts
- Fits well with 〜そうです reporting style
人がたくさんいる
- More concrete, like “there are a lot of people (there)”
- Feels a bit more casual / conversational and more like you are observing actual numbers right now

Since the sentence is describing a general tendency and ends with 〜そうです (hearsay), 人が多い is a natural, slightly more formal/neutral choice.

Why use たり…たり instead of just 読んで、星を見て?

Compare:

読んで、星を見て
- Simply connects actions in order: “read and (then) look at stars”
- Feels like you’re listing all the actions you did, or describing a specific sequence
読んだり、星を見たりする
- Lists examples of things one might do: “do things like read and look at stars”
- Implies there may be other similar activities and focuses on the type of activities, not a strict sequence

Since the sentence is about what children typically do that leads them to become interested in astronomy, the speaker wants to say:

“When they do things like reading space books and looking at stars (among other similar things), …”

So たり…たりする is more appropriate than a simple 〜て、〜て list.