"I eat at noon."
Translation:Yo como al mediodía.
"en" = "at" is not a hard and fast definition. referring to time, "at" is often "a" (at 4 o'clock is "a las 4) "al" is the combination of "a" and "el", and whenever the two combine that way they join to form "al." That is one of the only two contractions in Spanish, de+el = del being the other. what you got here is " a el mediodia" = "al medioda" = at the mid-day.
'dia' is an exception, in that it ends with 'a' and is masculine.
Not female, which implies sex, but feminine which implies gender (which is different to linguists than it is to us other folks). Nouns have gender, which means that a feminine noun requires feminine modifiers, but none of them are females.
No offense to the people who run this site, but I think if you have a problem etc. with a translation, then I do not advise relying SOLELY on this site for it. This applies for all things on here. And plus, in a language course there are bound to be exceptions, errors etc. Learning's not an easy, nor smooth process, believe me.
Still confused? This IS the Internet. ;)
I think the tilde is used to show that "the 'i' is not part of a diphthong (as in the pronunciation of piano), but a separate syllable. http://www.elearnspanishlanguage.com/pronunciation/diphthongs.html
the word pairs are day-night (dia-noche) and midnight-noon (media noche-mediodía)
Mediodía is not an interval of time, but a specific instant of the day.
For things done at specific instants, you use "a la" (femenina) or "al" (masculino) "a la media noche", "al mediodía"
For things done during intervals of time, you use "durante" or "por" (durante is prefered since it's less ambiguous) "durante el día", "durante la noche"