Time interval terminology

[1940LaSalle]

TL;DR

Exploring the ambiguous word "day " and a search for precise alternatives

The word "day" has at least two if not more common connotations:
1. The interval required for earth to make one rotation about its axis; i.e., ~24 hours.
2. The variable interval between sunrise and sunset.

I'm looking for unambiguous terms to differentiate the two such that one could say, "On 9 August, the [interval between sunrise and sunset] decreased to just under 14 hours.", or "In [six intervals of 24 hours], it will be Thursday, 15 August. ", where in each case the [phrase in brackets] would be replaced by one east-to-remember wotd.

 

[renormalize]

TL;DR Summary: Exploring the ambiguous word "day " and a search for precise alternatives

I would say:
"On 9 August, the daytime (or perhaps daylight-time) decreased to just under 14 hours." and "In six days, it will be Thursday, 15 August. "

 

[berkeman]

TL;DR Summary: Exploring the ambiguous word "day " and a search for precise alternatives

The word "day" has at least two if not more common connotations:
1. The interval required for earth to make one rotation about its axis; i.e., ~24 hours.
2. The variable interval between sunrise and sunset.

I'm looking for unambiguous terms to differentiate the two

What have you found with your Google searching? What have you found for scientific definitions of the term length of day on Earth?

Edit/Add:

Spoiler

https://en.wikipedia.org/wiki/Day

 

[Baluncore]

I'm looking for unambiguous terms to differentiate the two ...

The reason why you need a precise term, will determine what the term is, and how you define that term.

Will the statements be made by people who know the difference between the synodic day and the sidereal day? Will they live in the tropics where there are two summers each calendar year, in temperate regions where the seasons are simpler, or in a dark polar region where this year, the last sunset will be in late November?

Latitude makes a difference, but so does longitude. Communications involves different time zones, while travel involves the date line. Each time you travel once around the Earth, do you age a day more or less than your twin who stays at home.

Naive humans could just use the word day, then let the historians argue. Human language has been imprecise in the past. The age of Methuselah when he died was 969 periods of time. Was that solar years, or lunar months making 75 solar years?

On average, over one year, the days are longer than the nights. That is because the Sun has a finite diameter, and the atmosphere refracts light over the horizon. Dusk and dawn happen faster, and more regularly, in the tropics.

 

[AlexB23]

TL;DR Summary: Exploring the ambiguous word "day " and a search for precise alternatives

The word "day" has at least two if not more common connotations:
1. The interval required for earth to make one rotation about its axis; i.e., ~24 hours.
2. The variable interval between sunrise and sunset.

I'm looking for unambiguous terms to differentiate the two such that one could say, "On 9 August, the [interval between sunrise and sunset] decreased to just under 14 hours.", or "In [six intervals of 24 hours], it will be Thursday, 15 August. ", where in each case the [phrase in brackets] would be replaced by one east-to-remember wotd.

Well, one solar day is 86,400 seconds, while the daytime is the time between sunrise and sunset.

 

[Herman Trivilino]

TL;DR Summary: Exploring the ambiguous word "day " and a search for precise alternatives

1. The interval required for earth to make one rotation about its axis; i.e., ~24 hours.

The time to make one rotation is about 23 hours, 56 minutes. The so-called sidereal day. 24 hours is a solar day. I don't know of a single word for that.

The day describing the period of daylight, as in the phrase "now that summer is here the days are longer", is harder to define because there is no precise way to determine when the dark of night changes to the light of day, or vice-versa. I don't know of a single word for that, either.

Context usually makes it clear which one you mean.

 

[Baluncore]

... 24 hours is a solar day. I don't know of a single word for that.

The astronomical term is "Synodic Day", because that Earth rotation is measured relative to the Sun, not (sidereal) the stars.

The day describing the period of daylight, as in the phrase "now that summer is here the days are longer", is harder to define because there is no precise way to determine when the dark of night changes to the light of day, or vice-versa. I don't know of a single word for that, either.

The term for that period is "twilight", with the instants being "dusk" or "dawn".
Day and night refer to the sunlit and dark periods of the 24 hour daily cycle. Sunrise or sunset is when the upper limb of the Sun passes the horizon. In the morning and evening, there is a transition called twilight, which is subdivided into three parts, based on purpose, and on the depression below the horizon, of the upper limb of the Sun.
Day. >0°.
Sunrise or sunset. =0°. Colloquial dawn or dusk is at 0°.
Civil twilight. -0° to -6°. Civil dawn or dusk is at -6°.
Nautical twilight. -6° to -12°. Nautical dawn or dusk is at -12°.
Astronomical twilight. -12° to -18°. Astronomical dawn or dusk is at -18°.
Night. <-18°.