# Understanding the difference between second and moment

Below are the two sentences. Which one should be used and when?

The Earth is protected every second.

The Earth is protected every moment.

• Although second and moment are practically synonyms, "every" and "all" are not. The phrase "every second" does not mean "at all times". Every second refers to a frequency.
– TimR
May 9, 2016 at 9:46
• @TRomano, is moment countable ?? I know second has life span of one second, but what is the life span of moment ? May 9, 2016 at 9:50
• The lifespan of a moment, although it may be indefinite, is a span nonetheless.
– TimR
May 9, 2016 at 9:51
• @TRomano that is what i am telling how both are same then ?? May 9, 2016 at 9:51
• I don't understand your last remark. But the two words are synonymous insofar as they refer to a span of time and an instant of time. Consider: may I have a half of your sandwich? May I have a piece of your sandwich? "Piece" is not exact like "half". "Moment" is not exact like "second".
– TimR
May 9, 2016 at 9:53

The pedantic answer is that a second is an SI unit of time with a precisely defined duration and that a moment is just a short period of time of arbitrary duration.

In common usage though, the two terms are effectively synonymous. In your example sentences both will be readily understood as meaning that the Earth is continuously protected.

Whether you use second or moment in writing such as this is a matter of style and preference.

• +1 for pointing out the unusual fact that "one second" does not always equal 1 second. When a clerk says, "I'll be with you in one second," that doesn't mean "in 1/60th of a minute. It means, well, "in a few moments."
– J.R.
May 9, 2016 at 14:22
• If we're being pedantic: in medieval times, a moment was a measure of time, on average about 90 seconds. May 9, 2016 at 14:38

A moment is an ambiguous unit of time, it could be anywhere between a few milliseconds and 3 seconds (not necessarily limited to 3 seconds).

A second is a precise unit of time, precisely equal to 9,192,631,770 cycles of the radiation that gets an atom of the element called cesium to vibrate between two energy states1.

• I'm not sure if you meant "3 seconds" literally. As you say, a moment is an ambiguous amount of time, it could easily be more than 3 seconds. I'm not sure what the absolute upper bound would be.
– Jay
May 9, 2016 at 21:29
• @Jay I think the upper bound even goes up the further a moment is in the past. We can think of the big bang as a moment without much trouble, even though the entire event took billions of years. May 10, 2016 at 7:57
• That bit about the cesium atom is interesting, and even a little funny, but, for the sake of completeness, you really should mention that a second is also an imprecise unit of time, roughly synonymous with moment.
– J.R.
May 10, 2016 at 7:59
• @J.R. As with most things in the English language, we're both correct and it depends entirely on context. I'm sure a second would be a precise measure of time in certain fields, see Atomic Clocks, But I could also say "I'll be 1 second" which could mean a couple of minutes. May 10, 2016 at 8:10
• Oh, yes, I didn't mean to say that a second was never used as a precise measure. It is – in science, and in sports. No commentator would ever say, "There are 3.6 moments left in this basketball game."
– J.R.
May 10, 2016 at 8:14