Which of the following statements best explains why the scientific search for extraterrestrial life generally focuses on looking for life that is at least somewhat like life on Earth?
Responses
We have good reasons to think that all life in the universe would share the same biochemistry as life on Earth.
We have good reasons to think that all life in the universe would share the same biochemistry as life on Earth.
According to the established definition of life, Earth-like life is the only type of life that can exist.
According to the established definition of life, Earth-like life is the only type of life that can exist.
It is possible that life very different from life on Earth might exist, but it would be scientifically uninteresting.
It is possible that life very different from life on Earth might exist, but it would be scientifically uninteresting.
This is the only type of life that we can be confident we would recognize as life.
**Answer:** This is the only type of life that we can be confident we would recognize as life.
Quick why: we’ve got one verified data point (Earth), our instruments and biosignature models are tuned to it (liquid water, carbon chemistry, atmospheric disequilibria like O₂ + CH₄), and “weird life” might exist but we wouldn’t know what to look for—classic “search under the lamppost” logic.
What is astrobiology?
Responses
The search for alien civilizations
The search for alien civilizations
The study of life found on other worlds
The study of life found on other worlds
The study of life on Earth and of the possibility of life beyond Earth
The study of life on Earth and of the possibility of life beyond Earth
The study of the potential for life elsewhere in the universe, but not including the study of any life on Earth
The study of the potential for life elsewhere in the universe, but not including the study of any life on Earth
The study of the lives of stars
**Answer:** The study of life on Earth and of the possibility of life beyond Earth.
Why: Astrobiology covers origins, evolution, and distribution of life—using Earth as the only confirmed example while hunting for others out there.
Our best evidence concerning when Earth began to form comes from ________.
Responses
theoretical modeling of how the planets formed
theoretical modeling of how the planets formed
radiometric dating of the oldest Earth rocks
radiometric dating of the oldest Earth rocks
radiometric dating of the oldest meteorites
radiometric dating of the oldest meteorites
carbon-14 dating of the oldest fossils
**Answer:** radiometric dating of the oldest meteorites.
Why: Earth’s rocks got recycled; meteorites are Solar System time capsules (~4.56–4.57 billion years). Carbon-14 is way too short-range.
Stupid question is incomplete: If we sent one of our current spacecraft to a nearby star (besides the Sun), the trip would take about ________.
Responses
1,000 years
1,000 years
100 years
100 years
10 years
10 years
100,000 years
**Answer:** 100,000 years.
Why: Our fastest probes crawl at ~15–17 km/s (~0.00005c). To Proxima Centauri (~4.24 ly) that’s on the order of 10^5 years—tens of thousands to ~100k. Not exactly a weekend road trip.
Stupid since it didn’t give a rate of travel – sure current probes – but we could hitch on Atlas 3i and get to 60 km/s. Or windsails or fusion…
Totally fair gripe. The MCQ hides the speed. Here’s the sanity check to Proxima Centauri (~4.24 ly), assuming simple cruise (no accel/decel):
| Cruise speed | Fraction of c | Rough travel time |
|—|—:|—:|
| 17 km/s (Voyager-ish) | 0.000057c | ~75,000 years |
| **60 km/s** (your “Atlas” boost) | 0.00020c | **~21,000 years** |
| 200 km/s (Parker-like peak) | 0.00067c | ~6,400 years |
| 1,000 km/s (wild for “current”) | 0.0033c | ~1,270 years |
| 0.001c (0.1% light speed) | — | ~4,250 years |
| 0.01c (1%) | — | ~425 years |
| 0.1c (10%) | — | ~42 years |
| 0.2c (Starshot-style laser sail) | — | ~21 years |
So yeah—**with today’s *actual* spacecraft** you’re stuck in the tens-of-thousands-of-years club. Even 60 km/s only buys you “mere” 20 millennia. To get human-lifetime trips you need ≥0.1c, which means tech we don’t have flying yet (beam-driven sails, serious fusion, etc.).
“Hitching” on a fast interstellar object sounds fun, but those guys zip through at tens of km/s relative to the Sun—great for headlines, still not even 0.1% of c. You need relativistic fractions to make Proxima a road trip, not a civilization project.
Earth is slightly closer to the Sun in January than July. Hows does the area swept out by Earth’s orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?
Responses
Both areas are equal.
Both areas are equal.
The area swept out in July is larger.
The area swept out in July is larger.
The area swept out in January is larger.
**Answer:** Both areas are equal.
Kepler’s 2nd law: equal areas in equal times. January = July in days → same swept area, even though Earth moves a bit faster in January (near perihelion) and slower in July (near aphelion).
Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?
Responses
the Milky Way is composed of many individual stars
the Milky Way is composed of many individual stars
phases of Venus
phases of Venus
four moons of Jupiter
four moons of Jupiter
patterns of shadow and sunlight near the dividing line between the light and dark portions of the Moon’s face
**Answer:** phases of Venus.
Why: Only a Sun-centered Venus can show the full range of phases (including “full” with a small apparent size). Jupiter’s moons just prove not everything orbits Earth; Venus’s phases nail that *Venus orbits the Sun*.
**Answer:** phases of Venus.
Why: Venus shows the full set of phases (including “full” when it’s on the far side of the Sun), which only makes sense if **Venus orbits the Sun**—a direct Copernican mic-drop.
According to Newton’s universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them ________.
Responses
increases by a factor of 9
increases by a factor of 9
decreases by a factor of 3
decreases by a factor of 3
increases by a factor of 3
increases by a factor of 3
decreases by a factor of 9
**Answer:** decreases by a factor of 9.
Inverse-square law: (F propto 1/r^2). Triple (r) → (F) becomes (1/3^2 = 1/9) of what it was.
how many stars in the MW? Like 800 billion?
Short version: not 800 billion. Best mainstream range is **~100–400 billion stars** in the Milky Way. The spread comes from dust blocking our view and uncertainties in the stellar mass function. Gaia has precisely mapped ~2 billion stars so far—only a few percent of the total—so the final tally’s still fuzzy. citeturn0search11turn0search7
If you sneak in **brown dwarfs** (“failed stars”), you can add a few × 10¹⁰ more, but that still doesn’t push a solid estimate to 800 B for *stars*. citeturn0search12turn0search5
Rule of thumb: say “a few × 10¹¹ stars,” and you’ll sound both accurate and annoyingly reasonable.
Big Bang Stellar Interiors Stellar Explosions. H, He, C, Fe, AU
Big Bang Stellar Interiors Stellar Explosions. H, He, C, Fe, AU — does anyone belong in more thasn one category
That’s the cosmic “periodic table of origins.” Here’s the breakdown:
– **Big Bang → H, He (and a whisper of Li):**
The universe’s first 3 minutes produced almost all hydrogen and helium, plus trace lithium. Nothing heavier—too hot and too fast for nuclear furnaces to build beyond.
– **Stellar Interiors → C, O, up through Fe:**
Stars act like fusion factories. Small stars fuse H → He. Bigger stars keep going: He → C, O, Ne, Mg, Si … up until iron (Fe). Iron is the dead end, since fusing it *absorbs* energy instead of releasing it.
– **Stellar Explosions (supernovae, neutron star mergers) → AU (gold) and beyond:**
When massive stars blow or when neutron stars collide, the rapid neutron capture process (r-process) forges the heaviest elements—gold (Au), uranium, platinum, etc. These are cosmic fireworks that scatter the heavy metals we wear and mine.
So: **H & He = Big Bang. C–Fe = stellar cores. Au & other heavies = cataclysms.**
Want me to sketch this as a simple “origin → element” chart for quick reference?
Nice synthesis question. Let’s line them up:
– **Big Bang nucleosynthesis (first few minutes):** hydrogen (H), helium (He), tiny traces of lithium/beryllium. Nothing heavier.
– **Stellar interiors (fusion cores):** stars fuse H → He, then He → C, O, etc. In massive stars, you can climb the ladder up to **iron (Fe)**. Fusion stalls there.
– **Stellar explosions (supernovae, neutron star mergers):** make the *heaviest stuff* via rapid neutron capture—so that’s **gold (Au)**, uranium, etc.
Now to your question:
– **H, He** → Big Bang only.
– **C** → made in stellar interiors (triple-alpha).
– **Fe** → made in stellar interiors (end of fusion line) *and* explosively dispersed in supernovae.
– **Au** → not in normal stars; made in supernovae/mergers.
So the overlap candidate is **iron (Fe)**: forged in stellar interiors *and* distributed/partly synthesized in stellar explosions.
👉 Answer: **Fe belongs in more than one category.**
How can we use the fact that iron absorbs energy than realeasing it?
Where are different elements created?
Big Bang Stellar Interiors Stellar Explosions — H, He, C, Fe, AU
Great question—iron being the “fusion dead end” is actually a *feature* the universe uses in a few ways. Here’s how we exploit that fact:
—
### 1. **Understanding Stellar Deaths**
– When a massive star builds up an iron core, fusion can’t provide outward pressure anymore because iron fusion *consumes* energy instead of releasing it.
– That collapse → rebound → **supernova**.
– By recognizing this “iron limit,” we can predict which stars explode and when.
—
### 2. **Energy Calculations in Astrophysics**
– Knowing iron fusion is endothermic lets astrophysicists model energy budgets.
– Example: when core collapse begins, the gravitational potential energy (~10⁴⁶ joules) dwarfs the binding energy of the iron, driving the shockwave and neutrino flood.
– Without this principle, simulations wouldn’t match observed supernova light curves.
—
### 3. **Cosmic Element Distribution**
– The “iron barrier” forces nature to use **explosive processes** (supernovae, neutron star mergers) to build anything heavier than Fe.
– That tells us: if you see gold, uranium, or platinum, it’s proof that cataclysmic events seeded them.
—
### 4. **Human Tech (Indirect)**
– In nuclear physics, the iron “sweet spot” helps explain why both **fission** (splitting heavy nuclei like uranium) and **fusion** (combining light nuclei like hydrogen) release energy: both move nuclei *toward* iron’s binding energy per nucleon.
– That’s why nuclear power works at all—we’re just leveraging the same binding energy curve.
—
👉 So in short: the fact that iron fusion *absorbs* energy sets the stage for stellar collapse, supernova explosions, heavy-element creation, and even our own nuclear tech.
Do you want me to sketch the **binding energy per nucleon curve** (with H → Fe → U) so you can see visually why iron is the “energy valley”?
Here’s the clean breakdown for where those specific elements come from:
**Big Bang nucleosynthesis (first few minutes of the universe):**
– **Hydrogen (H)** – overwhelmingly produced in the Big Bang.
– **Helium (He)** – about 25% of the early universe’s mass; also Big Bang product.
**Stellar interiors (fusion inside stars):**
– **Carbon (C)** – formed in red giants through the triple-alpha process (He → C).
– **Iron (Fe)** – produced at the end of stellar fusion chains in massive stars (though stars can’t gain net energy from fusing Fe; it’s the “end of the road” for core fusion).
**Stellar explosions (supernovae / neutron star mergers):**
– **Iron (Fe)** – while forged in stellar interiors, much of the Fe we see is expelled and seeded into space during supernova explosions.
– **Gold (Au)** – created in extreme environments via rapid neutron capture (the r-process), mostly in supernovae and especially neutron star mergers.
👉 So, in table form:
| Element | Origin |
|———|——–|
| H | Big Bang |
| He | Big Bang |
| C | Stellar interiors |
| Fe | Stellar interiors **and** Stellar explosions |
| Au | Stellar explosions |
Would you like me to expand this into a **bigger periodic table “roadmap”** (showing where groups of elements—like oxygen, silicon, uranium—fit) so you’ve got a ready reference beyond just these five?
When we say that the Universe is expanding, we mean that…
Responses
the distance between stars in a galaxy get larger with time
the distance between stars in a galaxy get larger with time
galaxies are traveling through space at high speed
galaxies are traveling through space at high speed
all objects in the universe, including planets and stars, grow larger with time
all objects in the universe, including planets and stars, grow larger with time
galaxies are, on average, becoming farther apart with time
This book adds Helium to stellar interiors
**Answer:** galaxies are, on average, becoming farther apart with time.
Why: Expansion means **space itself is stretching**, increasing the distances *between* galaxies (on large scales). Stars inside galaxies aren’t being pushed apart, nor are planets swelling; local gravity holds those systems together. It’s the cosmic web that’s inflating.
Right — that’s not a mistake so much as a matter of *which* helium you’re talking about.
– **Big Bang helium:** About 25% of the baryonic mass of the universe formed as helium-4 during the first few minutes after the Big Bang. That’s the *primordial* helium.
– **Stellar helium:** Stars keep making more helium today, every time they fuse hydrogen in their cores. That’s why your book lists **helium under stellar interiors too** — it’s both a primordial element and a constant by-product of stellar fusion.
So helium gets **two stamps in its passport:**
– Born in bulk in the **Big Bang**
– Replenished daily in **stellar interiors**
That’s also why helium abundance is such a useful “cosmic check.” The ~25% baseline comes from Big Bang nucleosynthesis, while local variations on top of that come from stellar processing.
Want me to sketch you a neat **overlap chart** (like a Venn diagram) showing which elements belong in multiple categories? That might clear the fuzziness about things like helium and iron.
Carbon is 6 6 6 ?
bandwidth = speed
thread deleted
Pretty much! Here’s the breakdown of carbon’s “666” identity:
– **Atomic number = 6** → Carbon has 6 **protons** in its nucleus.
– **Neutral atom = 6 electrons** → Balances the 6 protons.
– **Common isotope = Carbon-12** → Has 6 **neutrons** in the nucleus.
So, the “6-6-6” shorthand works if you mean:
– 6 protons, 6 neutrons, 6 electrons → carbon-12.
But careful: not all carbon isotopes are that neat. Carbon-13 has 7 neutrons, Carbon-14 has 8. The “666” version is just the stable, garden-variety carbon we’re made of.
Do you want me to show you how this ties into the **periodic table slotting** (Z = 6, Group 14, 2s²2p² configuration), or just stick with the numerology vibe?
Not quite — bandwidth and speed are cousins, not twins.
– **Bandwidth** = the *capacity* of a channel. Think of it as the width of a highway (how many lanes you have). It’s measured in hertz (for frequency ranges) or in bits per second (for data transfer capacity).
– **Speed (latency / throughput)** = how *fast* something travels or gets delivered. For networks, it’s often used loosely to mean “how quickly I can download a file,” but technically that’s throughput — how much data per second you’re actually moving. Latency is another piece: the delay between sending and receiving.
👉 Example: You can have a wide highway (high bandwidth), but if there’s a traffic jam (congestion, protocol overhead, high latency), your *actual speed* of getting from A to B isn’t great. Conversely, a narrow highway with no traffic might deliver data steadily but slowly.
So: **bandwidth is potential capacity; speed is realized performance.**
Want me to give you a quick **table of networking terms** (bandwidth vs. throughput vs. latency vs. jitter) so you’ve got a clean reference for your CIT networking course?
Got it — that whole thread’s wiped. We’re starting fresh from here.
Want me to rebuild a compact version of the **element origins chart** we were working on, or leave it closed and move on?
Well maybe THAT is the mark of the beast!
What is the definition of bandwidth?
Multiple choice question
radio_button_unchecked
The speed of bits across the media over a given period of time
radio_button_unchecked
The speed at which bits travel on the network
radio_button_checked
The amount of data that can flow from one place to another in a given amount of time
radio_button_unchecked
The measure of usable data transferred over a given period of time
You wouldn’t be the first to make that connection—“666” has a certain infamous resonance thanks to Revelation. But in reality, carbon’s **6 protons, 6 neutrons, 6 electrons** is just physics doing its bookkeeping.
If you wanted to stretch it into symbolism:
– Carbon is the **basis of all life** (organic chemistry = carbon chemistry).
– Humans are carbon-based life forms → in a way, we *are* “marked” with 666.
– The “mark of the beast” could be read metaphorically as the **mark of being flesh-and-blood, mortal, material beings**, bound to Earthly existence.
Of course, that’s blending science with theology and a touch of poetic speculation. The Bible’s use of 666 is numerological, tied to gematria (letters-as-numbers) and politics of the day (many scholars point to it encoding “Nero Caesar”).
But if you wanted to play with the symbolism: yes—life itself, written in carbon, wears a little “666 badge” whether it likes it or not.
Want me to sketch how that idea might weave into your **Book of Rick**—like “the beast’s mark is just carbon, and carbon is us”?
✅ **Correct choice:**
**The amount of data that can flow from one place to another in a given amount of time.**
That’s the formal definition of **bandwidth** — it’s about *capacity*, not the literal “speed” of bits in the medium (those are always near light speed in fiber/copper).
The trick in multiple-choice land is:
– “Speed” answers are tempting but misleading.
– “Usable data” → that’s closer to *throughput*, the real-world rate after overhead.
So bandwidth = **maximum potential rate**, throughput = **actual achieved rate**.
The region of our solar system between Mercury and Mars has very few asteroids, while the region between Mars andJupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?
Responses
All the asteroids that formed between Mercury and Mars later migrated to the asteroid belt between Mars and Jupiter.
All the asteroids that formed between Mercury and Mars later migrated to the asteroid belt between Mars and Jupiter.
It was too hot for asteroids to form in this part of the solar system.
It was too hot for asteroids to form in this part of the solar system.
Gravity was too weak to allow asteroids to form in this part of the solar system.
Gravity was too weak to allow asteroids to form in this part of the solar system.
There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed.
While trying to solve a network issue, a technician made multiple changes to the current router configuration file. The changes did not solve the problem and were not saved. What action can the technician take to discard the changes and work with the file in NVRAM?
Multiple choice question
radio_button_checked
Issue the reload command without saving the running configuration.
radio_button_unchecked
Delete the vlan.dat file and reboot the device.
radio_button_unchecked
Close and reopen the terminal emulation software.
radio_button_unchecked
Issue the copy startup-config running-config command.
**Answer:** There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed.
Why:
– Inside the orbit of Mars, the solar nebula had plenty of solid material—but it didn’t stay loose for long.
– Mercury, Venus, Earth, and Mars scooped up nearly everything nearby during accretion.
– Jupiter’s strong gravity *prevented* planet formation further out, leaving a messy asteroid belt.
– So the difference isn’t that asteroids “migrated away” or “couldn’t form,” but that **inner planets hogged the leftovers**, while outer material stayed scattered.
✅ **Correct choice:**
**Issue the reload command without saving the running configuration.**
—
### Why:
– The **running configuration** lives in RAM — all active changes happen there.
– The **startup configuration** lives in NVRAM — that’s what the router loads after a reboot.
– If the technician hasn’t saved changes (`copy running-config startup-config`), then a **reload** will clear RAM and reload the saved config from NVRAM, effectively discarding the unsaved edits.
—
### Why the other options don’t fit:
– **Delete vlan.dat** → only affects VLAN database (mostly on switches), not the router’s running config.
– **Close and reopen terminal software** → just closes the admin’s session; the running config in RAM stays unchanged.
– **Copy startup-config running-config** → would *apply* the saved config on top of the running one without a reload, but it won’t wipe all the unsaved changes cleanly — some edits could remain active.
👉 Reload (without saving) is the clean, reliable reset.
Do you want me to also give you a **mnemonic or quick cheat sheet** for remembering where configs live (RAM vs NVRAM vs Flash) and which commands affect each? That’s a common test trap in CIT/CCNA.
The discovery of exoplanets has provided strong validation for the nebular theory, but it also forced scientists to recognize that the theory was incomplete (as it stood before the exoplanet discoveries).Which idea below was added to the theory after the discovery that some massive planets orbit very close to their stars?
Responses
Planets can migrate inward or outward from the orbits on which they originally formed.
Planets can migrate inward or outward from the orbits on which they originally formed.
Some young star systems have their cold regions, in which ices can condense, closer to their stars and the hot regions farther out.
Some young star systems have their cold regions, in which ices can condense, closer to their stars and the hot regions farther out.
Planets are expected to form on nearly circular orbits.
Planets are expected to form on nearly circular orbits.
Massive jovian planets sometimes form very close to their stars.
For the TCP/IP protocol suite, what is the correct order of events when a Telnet message is being prepared to be sent over the network?
Categories:
**Answer:** Planets can migrate inward or outward from the orbits on which they originally formed.
Why: Before exoplanet discoveries, the nebular theory assumed gas giants like Jupiter always formed *far out* where ices could condense. Then astronomers started finding **“hot Jupiters”**—massive planets practically hugging their stars. To explain this, scientists added the idea of **planetary migration**, where interactions with the protoplanetary disk or other bodies can shift a planet’s orbit dramatically after formation.
Good CIT/CCNA style question. For the **TCP/IP protocol stack**, the order of encapsulation when preparing a Telnet message is **Application → Transport → Internet → Network Access**.
Here’s the breakdown:
—
### 1. **Application Layer (Telnet)**
– The message originates from the Telnet application.
– Data is generated in a form the app understands.
### 2. **Transport Layer (TCP)**
– The Telnet data gets a **TCP header** (with source/dest ports, sequence numbers, etc.).
– Now it’s a TCP **segment**.
### 3. **Internet Layer (IP)**
– TCP segment is wrapped in an **IP header** (with source/dest IP addresses).
– Now it’s an IP **packet**.
### 4. **Network Access Layer (Ethernet/Physical)**
– IP packet is framed with **data link headers/trailers** (MAC addresses, error checking).
– It’s transmitted as a stream of **bits** on the physical medium.
—
👉 So the **correct order of events** when preparing a Telnet message:
**Telnet Data (Application) → TCP Segment (Transport) → IP Packet (Internet) → Frame/Bits (Network Access & Physical).**
—
Do you want me to also give you a **reverse-order view** (what happens on the receiving side as it unpacks the headers)? That often helps cement this in your head for test questions.
What is astrobiology?
Responses
The study of the potential for life elsewhere in the universe, but not including the study of any life on Earth
The study of the potential for life elsewhere in the universe, but not including the study of any life on Earth
The study of life found on other worlds
The study of life found on other worlds
The study of life on Earth and of the possibility of life beyond Earth
The study of life on Earth and of the possibility of life beyond Earth
The study of the lives of stars
The study of the lives of stars
The search for alien civilizations
**Answer:** The study of life on Earth and of the possibility of life beyond Earth.
Astrobiology isn’t just about aliens—it’s about:
– How life began and evolved on Earth (our only proven case).
– What conditions allow life to thrive elsewhere.
– Where and how we might detect signs of life in the universe.
So it’s the bridge discipline linking **biology, astronomy, geology, and chemistry** in the quest to understand life’s cosmic context.
Which of the following statements best explains why the scientific search for extraterrestrial life generally focuses on looking for life that is at least somewhat like life on Earth?
Responses
We have good reasons to think that all life in the universe would share the same biochemistry as life on Earth.
We have good reasons to think that all life in the universe would share the same biochemistry as life on Earth.
This is the only type of life that we can be confident we would recognize as life.
This is the only type of life that we can be confident we would recognize as life.
According to the established definition of life, Earth-like life is the only type of life that can exist.
According to the established definition of life, Earth-like life is the only type of life that can exist.
It is possible that life very different from life on Earth might exist, but it would be scientifically uninteresting.
**Answer:** This is the only type of life that we can be confident we would recognize as life.
Why:
– We only have **one data point—Earth**—so our search criteria (water, carbon chemistry, energy sources) are tuned to what we know.
– Life could exist in wildly different forms, but we wouldn’t necessarily recognize or detect it with current instruments.
– So scientists focus on **Earth-like biosignatures** not because they’re the *only* possible forms of life, but because they’re the only ones we’re sure we’d spot if they were out there.
For most of the ancient Greek philosophers, the lack of observable stellar parallax was interpreted to mean that ________.
Responses
Earth is stationary at the center of the universe
Earth is stationary at the center of the universe
stars were too far away for parallax to be measured with available technology
stars were too far away for parallax to be measured with available technology
stars must all lie at the same distance from Earth, on the celestial sphere
stars must all lie at the same distance from Earth, on the celestial sphere
Galileo’s theories of the universe were essentially correct
**Answer:** Earth is stationary at the center of the universe.
Why: Ancient Greek philosophers (like Aristotle and Ptolemy later) reasoned that if Earth orbited the Sun, nearby stars should appear to shift against the background over the year (stellar parallax). No such shift was seen with their naked-eye methods. Instead of realizing the stars were simply **too far away** to detect parallax with ancient technology, they concluded Earth must not move at all and therefore sits at the universe’s center.
(The “too far away” explanation is the *correct* one, but it wasn’t accepted until much later, when telescopes finally measured parallax in the 19th century.)