When Daniel was at least 80 years old around the year 538 B.C., he observes in Jeremiah's prophetic writings that the "desolation of Jerusalem" will end in 70 years.

In the first year of Darius the son of Ahasuerus, of Median descent, who was made king over the kingdom of the Chaldeans - in the first year of his reign, I, Daniel, observed in the books the number of the years which was revealed as the word of the Lord to Jeremiah the prophet for the completion of the desolations of Jerusalem, namely, seventy years. (Dan 9:1-2)

Therefore thus says the Lord of hosts, "Because you have not obeyed My words, behold, I will send and take all the families of the north," declares the Lord, "and I will send to Nebuchadnezzar king of Babylon, My servant, and will bring them against this land and against its inhabitants and against all these nations round about; and I will utterly destroy them and make them a horror and a hissing, and an everlasting desolation. Moreover, I will take from them the voice of joy and the voice of gladness, the voice of the bridegroom and the voice of the bride, the sound of the millstones and the light of the lamp. This whole land will be a desolation and a horror, and these nations will serve the king of Babylon seventy years. Then it will be when seventy years are completed I will punish the king of Babylon and that nation," declares the Lord, "for their iniquity, and the land of the Chaldeans; and I will make it an everlasting desolation. I will bring upon that land all My words which I have pronounced against it, all that is written in this book which Jeremiah has prophesied against all the nations." (Jer 25:8-13)

For thus says the Lord, "When seventy years have been completed for Babylon, I will visit you and fulfill My good word to you, to bring you back to this place." (Jer 29:10)

As Daniel gives his "attention to the Lord God" and sought Him "by prayer and supplications, with fasting, sackcloth and ashes" (Dan 9:2-3), God noticed and sent His angel Gabriel who informed Daniel, "At the beginning of your supplications the command was issued, and I have come to tell you, for you are highly esteemed; so give heed to the message and gain understanding of the vision" (Dan 9:23).

While Daniel sought to understand Jeremiah's prophecy of seventy years, and how God will bring His people back to Israel, Gabriel brings a message that speaks of seventy sevens. This was both unexpected and an enigma to Daniel.

Seventy weeks (Hebrew: shâbûa') have been decreed for your people and your holy city, to finish the transgression, to make an end of sin, to make atonement for iniquity, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy place. So you are to know and discern that from the issuing of a decree to restore and rebuild Jerusalem until Messiah the Prince there will be seven weeks (shâbûa') and sixty-two weeks (shâbûa'); it will be built again, with plaza and moat, even in times of distress. Then after the sixty-two weeks (shâbûa') the Messiah will be cut off and have nothing, and the people of the prince who is to come will destroy the city and the sanctuary. And its end will come with a flood; even to the end there will be war; desolations are determined. (Dan 9:24-26)

Bible translators have opted for two ways to translate the Hebrew term "shâbûa'":

"Weeks (or units of seven)" as seen in the NASB and NET translations and their footnotes.

"Sevens (or weeks)" as seen in the NIV and NKJV translations and their footnotes.

The Hebrew term "shâbûa'" is a quantitative unit that can be understood as "seven" but it also includes the meaning of fullness or a fulfilled and perfectly completed period. There are several examples that illustrate the significance and completeness of the number seven:

God's Creation took seven days (Gen 1:1 - 2:2). In this context, a unit of seven meant seven days.

The Law of Moses stipulated that the seventh day be a day of rest (Sabbath, Ex 20:8-11) and in a similar fashion, the land left to rest and lie fallow on the seventh year (Ex 23:10-11).

Jubilee occurred after "seven Sabbaths of years" or "seven times seven years" (49 years) in which the 50th year, an Israelite in the Promised Land will receive his inherited land back, leave it fallow for the year, and release any who were slaves (Lev 25:8-13). In this context, a unit of seven meant seven years.

As a completed period, the Hebrew term "shâbûa'" can refer to the quantity of seven days or seven years. In Greek, a set of seven is called a "heptad."

Two years later after the angel Gabriel's message, Daniel is seeing Jeremiah's prophecy beginning to be fulfilled which he indicates by the change in how the king is addressed, from "Darius" to "Cyrus the Persian" (Dan 10:1). But does Daniel understand the angel Gabriel's message? It appears not. Accustomed to seeing his prophecies fulfilled, Daniel waits for seventy seven day periods (490 days) to see God's unfolding plan, but nothing happens. Now two years later, after seventy seven day periods, Daniel once again gives his attention to the Lord God in prayer and supplication as he tries to understand Jeremiah's prophecy in light of the angel Gabriel's message (Dan 10:1-3). In response, he receives another angelic visitation:

Then he said to me, "Do not be afraid, Daniel, for from the first day that you set your heart on understanding this and on humbling yourself before your God, your words were heard, and I have come in response to your words. (Dan 10:13)

While Daniel has lived under two different Gentile kingdoms since the fall of Jerusalem, the angel tells him about the coming third Gentile kingdom (Dan 11:2-34; 8:21-27), which he now understands. However, Daniel still does not understand the angel Gabriel's message of seventy weeks (Dan 12:7-8) as well as the fourth kingdom (Dan 11:35-45; 7:19-28) that precedes the Divine Kingdom.

"Shâbûa'," as Daniel discovers, is not a period of seven days; it is a period of seven years. Daniel wants to know the outcome of God's plan; but, he is essentially told to not worry (Dan 12:8-9, 13).

When an angel speaks of "seventy weeks," what constitutes a year? Is it in the context of the Hebrew lunar calendar (354 days / year) or the Julian / Gregorian calendar (365 days / year), and what about leap years?

When God speaks of calendar time, He sees a year consisting of 12 months of 30 days each; thus, a calendar year of 360 days (12 x 30). Among theologians, this is called a "Prophetic Year."

An example of how God sees calendar time is in the duration of the Flood:

In the six hundredth year of Noah's life, in the second month, on the seventeenth day of the month, on the same day all the fountains of the great deep burst open, and the floodgates of the sky were opened. (Gen 7:11)

The water prevailed upon the earth one hundred and fifty days. (Gen 7:24)

and the water receded steadily from the earth, and at the end of one hundred and fifty days the water decreased. In the seventh month, on the seventeenth day of the month, the ark rested upon the mountains of Ararat. (Gen 8:3-4)

The Flood lasted exactly 5 months or 150 days; thus, one month was 30 days.

In another example is God's stipulation of a period of mourning for the passing of a loved one, which was one month or 30 days.

She shall also remove the clothes of her captivity and shall remain in your house, and mourn her father and mother a full month; and after that you may go in to her and be her husband and she shall be your wife. (Deut 21:13)

When all the congregation saw that Aaron had died, all the house of Israel wept for Aaron thirty days. (Num 20:29)

Unlike the Hebrew or Gregorian Calendars, the Prophetic Year does not make any adjustments for agricultural purposes or seasons (i.e. leap years).

By understanding what a Prophetic Year is, one can determine the corresponding Gregorian date to see if there are any historical events that fulfill the angel Gabriel's message to Daniel.