** The following calendar data of Holy Days is still being analyzed and is presented here to make future research by others easier. The number of days between "Holy Days" can be obtained by simply subtracting their Reference Days. For more information on the construction of the Jewish calendar. 
The Holy Days listed are:
Rosh Hashanah- The Jewish New Year on their modern calendar. The first day of the month of Tishri.  The seventh month of the Jewish calendar. The required time for the blowing of the trumpets. (Lev. 23:20) Rosh Hashanah will always occur in September or October of the year.
Yom Kippur- The Day of Atonement, the tenth day of the seventh month (Tishri) (Lev. 23:27)
Succoth- Feast of Tabernacles- begins the 15th day of the seventh month (Lev. 23:34)
Hanukah- Beginning of the Jewish Feast of Lights (not a Scriptural Holy Day, but included here because it is considered holy to modern Jews.
Christmas- a holy day to Christians, although the exact day of Jesus birth is questionable
New Year (Gregorian -- January 1) added for reference purposes only
Purim- (Feast of Lots) Jewish holy day recorded in the book of Ester when the Lord turned the tables on the enemies of the Jews.
Nisan 1- The first day of the first month of the year {First month according to Exodus 12:2}
Nisan 14- Biblical Passover (Lev. 23:5)
Nisan 15- Modern Jewish Passover
Easter {Biblical} - First Fruits Offering- Sunday following the first Saturday which occurs on or after the Biblical Passover in accordance with the holy day of Jesus' resurrection. (Lev. 23:10-11)
Easter {Modern}- The first Sunday, after the fourteenth day of the ecclesiastical moon {nearly full moon} which occurs on or after the vernal equinox. Easter is computed according to the Gregorian method after 1582 A.D. [Easter can occur any time from March 22 to April 25.]
Israel's Birth-Jewish - Israel's re-birth on the Jewish Calendar {Iyar 5}
Israel's Birth-Gregorian - Israel's re-birth on the Gregorian Calendar {May 14}
Shavouth- 50 days from Modern Passover - Jewish Pentecost
Pentecost- 50 days from Modern Easter - Christian Pentecost
Ab 9- the 9th of the month of Ab, the day which according to Jewish tradition is the exact day that both temples were destroyed.

RD is for Reference Date computed from May 14, 1948 A.D., Iyar 5, 5708 C.E. [The day Israel became a nation.] {On my original calendar I had used September 15, 1947 A.D., Tishri 1, 5708 C.E. as the reference date, but have now changed it to the actual date of Israel's rebirth.} The following data is available in ASCII text format for computation:   rdcal.txt
The reference date can be computed by subtracting 2432685 from the astronomical Julian Star Date.
The Julian Star Date used by observatories and for space flights is computed from the arbitrary date of Jan. 1, 4713 B.C., at noon Greenwich mean time.

+ added for reference only
* non-Biblical modern Jewish holy day

The following data has been computed by a calendar program written for this purpose which is available upon request.  Jewish dates have been verified by using the book  Comprehensive Jewish Calendar  , by Arthur Spier {ISBN 0-87306-288-4}