<p>Here is the best answer I have seen to this:
<div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/urgYWNCN-R?start=0"></iframe>
            </div></div>
It works through the calculations using simple observations.</p>
<p>Cassini (the guy, not the spacecraft) calculated the distance to the Sun. See <a href="http://curious.astro.cornell.edu/about-us/41-our-solar-system/the-earth/orbit/87-how-do-you-measure-the-distance-between-earth-and-the-sun-intermediate" rel="nofollow noreferrer">http://curious.astro.cornell.edu/about-us/41-our-solar-system/the-earth/orbit/87-how-do-you-measure-the-distance-between-earth-and-the-sun-intermediate</a></p>
<p>Edmond Halley realised the transit of Venus across the Sun could be used to calculate the distance. NASA has a page explaining that: <a href="https://pwg.gsfc.nasa.gov/stargaze/Svenus1.htm" rel="nofollow noreferrer">https://pwg.gsfc.nasa.gov/stargaze/Svenus1.htm</a></p>
<p>Nowadays things are easier. We can easily find the distance to the Moon to centimeter accuracy by bouncing laser light from the reflectors left on the Moon during the Apollo program. We can use that to calculate the distance to the Sun.</p>

CC BY-SA 4.0
2021-03-27T14:51:14.177Z
Perhaps you could explain the method. The OP has been criticised for not doing exactly what you have done, which is just googled for an answer. Link-only answers add little value. In addition, your main link doesn't work.
ProfRob
CC BY-SA 4.0
2021-03-27T08:20:22.033Z
2021-03-27T08:20:22.033Z
Miriam English
<p>There are a bunch of ways.  The simplest is triangulation.</p>

<p>Consider a transit of Mercury or Venus, when the planet gets between the Earth and the Sun. If you observe the planet's path across the face Sun from two different places, measuring the chords across the Sun's disk and the timings, using no more than trigonometry, you can get an accurate distance to the Sun.</p>

<p>Here's a <a href="https://physics.stackexchange.com/questions/29363/how-did-halley-calculate-the-distance-to-the-sun-by-measuring-the-transit-of-ven">good discussion of the method on the Physics SE</a></p>

<p>(It's worth noting that it is easy to measure the distance to, say, Mars in terms of the <em>ratio</em> of the distance to Mars compared with the Earth-Sun distance, than it is to measure the Earth-Sun distance in miles.  Hence the Astronomical Unit.  We accurately knew many astronomical distances in AU before we knew the length of the AU equally accurately.)</p>

CC BY-SA 4.0
2019-06-17T12:12:08.960Z
In trigonometry you need two sides to calculate the third. The question is basically asking how the first two sides are generated specifically the second side. The first side is simple enough to measure, two points on earth (assuming a flat terrain) but the second is equally as difficult as generating the third. There is a lot that’s not properly accounted for in generating this distance
Autodidact
CC BY-SA 4.0
2019-06-17T12:27:02.240Z
We knew the two sides, in astronomical units (the distance of the Sun is 1AU, by definition). The point of the observation of transits was to measure a terrestrial distance in astronomical units. Unfortunately most explanations do not make that clear, confusing people like Autodidact who actually think clearly about the questions.
Martin Kochanski
CC BY-SA 4.0
2018-05-25T19:54:41.967Z
2018-05-25T19:54:41.967Z
Mark Olson
<p>How was the Earth to sun distance measured. How do we know how far from the Earth the Sun actually is.</p>

CC BY-SA 4.0
2018-05-25T19:47:16.317Z
Did you even try?  https://www.google.com/search?q=how+do+we+know+how+far+the+sun+is&rlz=1C1GNAM_enUS689US689&oq=how+do+we+know+how+far+th&aqs=chrome.1.69i57j0l5.8103j0j7&sourceid=chrome&ie=UTF-8
Phil N DeBlanc
CC BY-SA 4.0
2018-05-25T20:13:55.927Z
150million kilometer. 1 mile is around 1.6 km.
peterh
CC BY-SA 4.0
2018-05-25T20:16:22.113Z
Am I supposed to stump people with my question? I'm trying to understand things I don't know about.
user23178
CC BY-SA 4.0
2018-05-26T06:02:00.867Z
Very good thank you. I asked a question nobody knew the answer to and it got shut down for not being in the right category so I'm learning.
user23178
CC BY-SA 4.0
2018-05-26T06:03:33.717Z
Apparently I'm a scholar now so I'm making progress.
user23178
CC BY-SA 4.0
2018-05-26T07:16:59.660Z
@user23178  New posters don't always read the guidelines and that's the problem with your question.   Before you post a question on stack exchange, do a little research.  This isn't a question nobody knows the answer to, it's a very well known historical study and easily googled, but they had to wait for a Venus transit, which happens about twice a century.  This was a subject of significant anticipation after Newton worked out his laws of gravity and orbital periods because they had to wait for the Venus transit.  The reason it's not a good question is that it's well known and easily googled.
userLTK
CC BY-SA 4.0
2018-05-26T11:37:15.050Z
And I want to clarify, it's actually a very good question, it's just not a good question for the stack exchange format.
userLTK
<the-sun>
How was the distance from the Earth to the Sun determined
user23178
# How was the distance from the Earth to the Sun determined

(Asked by: username_0 on 2018-05-25)

How was the Earth to sun distance measured. How do we know how far from the Earth the Sun actually is.

**Tags:** the-sun

> **Comments:**
> **username_1**: Did you even try?  https://www.google.com/search?q=how+do+we+know+how+far+the+sun+is&rlz=1C1GNAM_enUS689US689&oq=how+do+we+know+how+far+th&aqs=chrome.1.69i57j0l5.8103j0j7&sourceid=chrome&ie=UTF-8  
> **username_2**: 150million kilometer. 1 mile is around 1.6 km.  
> **username_0**: Am I supposed to stump people with my question? I'm trying to understand things I don't know about.  
> **username_0**: Very good thank you. I asked a question nobody knew the answer to and it got shut down for not being in the right category so I'm learning.  
> **username_0**: Apparently I'm a scholar now so I'm making progress.  
> **username_3**: @username_0  New posters don't always read the guidelines and that's the problem with your question.   Before you post a question on stack exchange, do a little research.  This isn't a question nobody knows the answer to, it's a very well known historical study and easily googled, but they had to wait for a Venus transit, which happens about twice a century.  This was a subject of significant anticipation after Newton worked out his laws of gravity and orbital periods because they had to wait for the Venus transit.  The reason it's not a good question is that it's well known and easily googled.  
> **username_3**: And I want to clarify, it's actually a very good question, it's just not a good question for the stack exchange format.  

---

## 2 answers

### Answer by username_6 on 2018-05-25. Score: 7 | Accepted answer

There are a bunch of ways. The simplest is triangulation.

Consider a transit of Mercury or Venus, when the planet gets between the Earth and the Sun. If you observe the planet's path across the face Sun from two different places, measuring the chords across the Sun's disk and the timings, using no more than trigonometry, you can get an accurate distance to the Sun.

Here's a [good discussion of the method on the Physics SE](https://physics.stackexchange.com/questions/29363/how-did-halley-calculate-the-distance-to-the-sun-by-measuring-the-transit-of-ven)

(It's worth noting that it is easy to measure the distance to, say, Mars in terms of the *ratio* of the distance to Mars compared with the Earth-Sun distance, than it is to measure the Earth-Sun distance in miles. Hence the Astronomical Unit. We accurately knew many astronomical distances in AU before we knew the length of the AU equally accurately.)

> **Comments:**
> **username_7**: In trigonometry you need two sides to calculate the third. The question is basically asking how the first two sides are generated specifically the second side. The first side is simple enough to measure, two points on earth (assuming a flat terrain) but the second is equally as difficult as generating the third. There is a lot that’s not properly accounted for in generating this distance  
> **username_8**: We knew the two sides, in astronomical units (the distance of the Sun is 1AU, by definition). The point of the observation of transits was to measure a terrestrial distance in astronomical units. Unfortunately most explanations do not make that clear, confusing people like username_7 who actually think clearly about the questions.  

---

### Answer by username_4 on 2021-03-27. Score: 1

Here is the best answer I have seen to this:It works through the calculations using simple observations.

Cassini (the guy, not the spacecraft) calculated the distance to the Sun. See <http://curious.astro.cornell.edu/about-us/41-our-solar-system/the-earth/orbit/87-how-do-you-measure-the-distance-between-earth-and-the-sun-intermediate>

Edmond Halley realised the transit of Venus across the Sun could be used to calculate the distance. NASA has a page explaining that: <https://pwg.gsfc.nasa.gov/stargaze/Svenus1.htm>

Nowadays things are easier. We can easily find the distance to the Moon to centimeter accuracy by bouncing laser light from the reflectors left on the Moon during the Apollo program. We can use that to calculate the distance to the Sun.

> **Comments:**
> **username_5**: Perhaps you could explain the method. The OP has been criticised for not doing exactly what you have done, which is just googled for an answer. Link-only answers add little value. In addition, your main link doesn't work.  

---

