Talk:Rømer's determination of the speed of light

Comments by 82.108.99.124
I would suggest that the following is incorrect. "This would give light a velocity of about 220,000 kilometres per second in SI units, about 26% lower than the true value of 299,792 km/s."

The SI unit of length is the metre, and so the SI unit of speed is metre per second. The sentence should be re-written to reflect this, and should read something like "This would give light a velocity of about 220,000,000 metres per second in SI units, about 26% lower than the true value of 299,792,458 m/s." — Preceding unsigned comment added by 82.108.99.124 (talk) 13:22, 7 December 2016 (UTC)

I'm removing this sentence from the lead:

"While the exact details of Rømer's calculations have been lost, the error is probably due to an error in the orbital elements of Jupiter, leading Rømer to believe that Jupiter was closer to the Sun than is actually the case."

This is unsourced and appears to be incorrect. The error is due to the original measurement that 1 AU equals 11 minutes, while the correct measurement is 8 minutes 19 seconds, as detailed in the article. This has nothing to do with the distance to Jupiter.

If someone more knowledgable on this subject knows this to be incorrect, feel free to revert and explain.

Will Sandberg (talk) 01:03, 5 March 2015 (UTC)


 * Good catch, thanks. Chillum 04:39, 5 March 2015 (UTC)

Traité de la lumière
French spelling: "Traité de la lumière" not "Treatise" or "Traitée" Stefjourdan — Preceding unsigned comment added by 163.47.106.7 (talk) 21:12, 6 December 2016 (UTC)

Rømer's reasoning | Cumulative effect
The previous paragraph "Order of magnitude" ends with this sentence:

"In practice, no difference is observed at all, from which Rømer concludes that the speed of light must be very much greater than one Earth-diameter per second."

In this new paragraph, a cumulative effect is examined. I guess it is due to Jupiter moving relatively to Earth. So, Jupiter and Earth are getting closer or away from each other and speed of light determines an advance or delay of the observations. If this is really the reason behind the cumulative effect, I believe it should be made explicit. It would also help to better grasp the meaning of the last section "Later discussion | Doppler method".

PS: Isn't the time shift affected by both planets changing their position relatively to the sun too, since we see light reflected from Jupiter?--HannibalSmith~itwiki (talk) 19:21, 7 December 2016 (UTC)

The first quantitative estimate of the speed of light is seen in Indian vedic scholar Sayana’s commentary on the Rig Veda. It says that sun light travels 2,202 yojanas in the time span of a nimisharda (half a nimisha). The yojana is an ancient unit of length. Arthasastra defines it as being equal to 8,000 dhanus, which is equivalent to 9.09 miles. A nimisha is an ancient unit of time that is equal to 16/75 seconds. Thus 2,202 yojanas in half a nimisha is equal to 189,547 miles per second after conversion. The modern estimate of the speed of light is 186,281.7 miles per second.

This velocity of Light was calculated by Maxwell in the 19th century, but its was actually determined accurately thousands of years before in the Rig Veda. It was further elaborated by Sayana in the 14th century AD in his commentaries on Rig Veda. Indian Almanacs have always calculated accurately the motion of planets, sunset, sunrise, eclipses, etc. without using telescopes or any other machinery.

It is to be noted that Bhatta Bhaskara (probably from the 10th century) made the same statement in his commentary on Taittiriya Brahmana, another Hindu Veda. He says this to be an old tradition.

The fourth verse of the Rigvedic hymn 1:50 (50th hymn in book 1 of rigveda) is as follows:

तरणिर्विश्वदर्शतो जयोतिष्क्र्दसि सूर्य | विश्वमा भासिरोचनम |

taranirviśvadarśato jyotishkridasi sūrya | viśvamā bhāsirocanam ||

This means “Swift and all beautiful art thou, O Surya (Sun), maker of the light, illuminating all the radiant realm.”

Exlpaining this verse in his Rig Veda commentary, Sayana, who was a minister in the court of Bukka of the great Vijayanagar Empire of Karnataka in South India (in early 14th century), says:

tatha ca smaryate yojananam. sahasre dve dve sate dve ca yojane ekena nimishardhena kramaman.

This means “It is remembered here that Sun (light) traverses 2,202 yojanas in half a nimisha.”

Note: Nimisharda = half of a nimisha In the vedas Yojana is a unit of distance and Nimisha is a unit of time.

Unit of Vedic Time: Nimisha

The Moksha Dharma Parva of Shanti Parva in Mahabharata describes Nimisha as follows: 15 Nimisha = 1 Kastha 30 Kashta = 1 Kala 30.3 Kala = 1 Muhurta 30 Muhurtas = 1 Diva-Ratri (Day-Night) We know Day-Night is 24 hours So we get 24 hours = 30 x 30.3 x 30 x 15 nimisha in other words 409050 nimisha We know 1 hour = 60 x 60 = 3600 seconds So 24 hours = 24 x 3600 seconds = 409,050 nimisha 409,050 nimisha = 86,400 seconds 1 nimisha = 0.2112 seconds (This is a recursive decimal. The wink of an eye is equal to 0.2112 seconds.) 1/2 nimisha = 0.1056 seconds

Unit of Vedic Distance: Yojana

Yojana is defined in Chapter 6 of Book 1 of the ancient vedic text “Vishnu Purana” as follows:

10 ParamAnus = 1 Parasúkshma 10 Parasúkshmas = 1 Trasarenu 10 Trasarenus = 1 Mahírajas (particle of dust) 10 Mahírajas= 1 Bálágra (hair’s point) 10 Bálágra = 1 Likhsha 10 Likhsha= 1 Yuka 10 Yukas = 1 Yavodara (heart of barley) 10 Yavodaras = 1 Yava (barley grain of middle size) 10 Yava = 1 Angula (1.89 cm or approx 3/4 inch) 6 fingers = 1 Pada (the breadth of it) 2 Padas = 1 Vitasti (span) 2 Vitasti = 1 Hasta (cubit) 4 Hastas = a Dhanu, a Danda, or pauruSa (a man’s height), or 2 Nárikás = 6 feet 2,000 Dhanus = 1 Gavyuti (distance to which a cow’s call or lowing can be heard) = 12,000 feet 4 Gavyutis = 1 Yojana = 9.09 miles

Calculation of the Speed of Light from the Rig Veda:

So now we can calculate what is the value of the speed of light in modern units based on the value given as 2202 yojanas in 1/2 nimisha

= 2,202 x 9.09 miles per 0.1056 seconds = 20,016.18 miles per 0.1056 seconds = 189,547 miles per second

As per the Rig Veda the speed of light is 189,547 miles per second. As per modern science the speed of light is 186,000 miles per second! — Preceding unsigned comment added by 210.212.195.98 (talk) 13:10, 7 December 2016 (UTC)

Why are almost all of Roemer's observations (notes) made during day-time? — Preceding unsigned comment added by 77.56.38.116 (talk) 18:50, 28 May 2017 (UTC)

Eclipses of Io
At the bootom of this section, we have Earth moving away form Jupiter and Earth moving towards Jupiter. In both cases is states that the interval between eclipses is increasing. One of these surely should be decreasing. Russellhillyer (talk) 17:46, 5 March 2024 (UTC)