Today is the Day of the Blast (Yom Terua) (Numbers 29:1) or Memorial of the Blast (Leviticus 24:23).
Today we remember the day that God spoke to Hebrews at Mt. Sinai, at which time among other things, the sound (not blast though) of the Horn (Shofar) (not trumpet) was heard(Exodus 19:16). However, today we are commanded to use the Trumpets (not Horn/Shofar) to make a Blast (not Sound) to honor this day(Numbers 10:10).
As a note, it seems that the actual Horn/ Shofar (as in organic musical instrument) would be used only once every 50 years (once every Jubilee ), whereas during all other times the Trumpets (a metallic musical instrument) would've been used. (Leviticus 25:8-10)
Also, the Jewish tradition calls this day a "new year"/"rosh hashana". This is incorrect, as the text of Exodus 23:16 and Exodus 34:22 states, that today is a revolution (or turning point) of the year. After all, this is the 1st day of the 7th month of the Hebrew calendar (the middle of the year), not the 1st day of the first month.
In fact, the Pentateuch explicitly states that the New Year begins 14 days prior to Passover, in the month of Aviv (see Exodus 12:2).
Also, it is worthy to point out that the exact term "rosh hashana" does not occur anywhere in the text. The text, in Exodus 12:2 uses the term "rosh hodesh"/"first or head month". However, in the same verse there is a word "hashana", so in a way it is possible to call the 1st of Aviv a "new year" or rather - "first year". Perhaps such terminology of the text is due to the fact that the word "rosh" is properly translated as the "head" or "first", so to translate it as "new" would not be very accurate.
The only explanation to the Jewish tradition, is this time of the year is indeed the beginning of the new agricultural year, so it seems that this is how this term ("rosh hashana"), over time, replaced the actual commandments and terminology of the Pentateuch. And this is very sad.
Other than that, this day is an astronomically significant event - an Autumn Equinox (Southern Equinox).
This holy day is the forth out of five annual Hebrew holy days - see this table for detailed explanation. As on all such days, there is a prohibition to doing any work - just like on Sabbath.
You can also check out my last year's post on the Silver Trumpets here.
Have a great Day of the Blast!