Talk:ΔT

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Errors in edit made 15 June 2020

I have reverted this edit for two reasons, and made further corrections.

First, it changed "ΔT is a symbol for the change, Δ, of a time period, T" to "ΔT is a symbol for the change, Δ, of a quantity T." But later, the disambiguation page states "The symbols Δt and ΔT are commonly used in other contexts as follows." Plainly the structure of the disambiguation page is to list the main meaning in the lead paragraph, and list other meanings later in the disambiguation page. So something more specific than "a quantity T".

The paragraph had several other errors, such as improper use of the term "finite difference". I have changed it to read

ΔT is a symbol for the difference, Δ, between two time scales, Universal Time and Terrestrial Time, which results from a drift in the length of a day.

This change also eliminates the passage " with T representing the period of the Earth's rotation." T does not represent the period of the earth's rotation, it represents two different time scales. Points in time in either of the two scales would typically be represented as calendar dates and times, such as "June 15, 2020, 08:40 UT" or ""June 15, 2020, 08:40 TT", although many other representations are possible. Jc3s5h (talk) 12:42, 15 June 2020 (UTC)[reply]

To editor Jc3s5h: Actually it is still wrong, as Δ is not a quantity at all. It is an operator. If T is a quantity, then ΔT is how much it changed, not Δ. Zero^talk 15:40, 15 June 2020 (UTC)[reply]

I wonder if there is a conceptual collision between the normal mathematical notation

Δt

, meaning a change in the quantity

t

(usually time) in some arbitrary equation, and this specific notation with the meaning that Jc3s5h describes? --John Maynard Friedman (talk) 16:02, 15 June 2020 (UTC)[reply]

Yes, possibly. But I would still say that Δ alone has no meaning as a quantity. Rather, ΔT is the quantity, whether it is the change in one thing or the difference between two things. Zero^talk 16:09, 15 June 2020 (UTC)[reply]

When I was editing, I was thinking about trimming the material that suggests that Δ has some separate meaning apart from T. I'm leaning toward the view that "ΔT" is a unitary defined term, and the association of Δ with taking a difference would belong in a discussion of the etymology of ΔT, rather than treating it as having a meaning of its own in this context. Of course, any such discussion belongs in the ΔT article, not in this disambiguation page. Jc3s5h (talk) 18:00, 15 June 2020 (UTC)[reply]

I agree completely and removed the isolated Δ. Zero^talk 02:41, 16 June 2020 (UTC)[reply]

??

What is the difference between dlta ‏Ｔ and ‏Ｔ 78.175.251.168 (talk) 17:16, 23 November 2021 (UTC)[reply]

In the sciences, Δ is often used in connection with a variable to indicate a change or difference. In this case, the T loosely represents time, and when combined with Δ it means a change in time. In this case, it indicates the difference between two time scales.

As discussed in the section below, ΔT is a term with a specific meaning, and in this context, neither Δ nor T have a meaning by themselves. The description I gave in the previous paragraph just indicates what inspired the term ΔT. Jc3s5h (talk) 18:36, 23 November 2021 (UTC)[reply]

Drift in the beginning of a day

“ΔT (timekeeping) the difference between two time scales, Universal Time and Terrestrial Time, which results from a drift in the length of a day “ and a much bigger drift in the beginning of a day.

It is better to put TT before UT according to the definition of the ΔT. ΔT is a vector, not a scalar. 2A01:E0A:9EE:BD20:FB:E3BB:F521:91EC (talk) 14:08, 2 July 2024 (UTC)[reply]