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International Tropical Calendar

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The International Tropical Calendar (ITC) is the proposed tropical calendar by Dr. Vam based on Western Zodiac (Previously Astronomy) with the dates being permanently synchronized to the Gregorian Calendar. Until now, the Gregorian calendar is modernized using tropical year concept (365.2425 days per year), but the equinoxes and solstices occur in the middle of the months. This new tropical calendar aligns with the tropical astrological months.

Despite its name, this International Tropical Calendar is not part of the International Calendar set and is incompatible with it in part, e.g. first day of the week and date notation. In particular, it is different from the International Season Calendar and the International Trimester Calendar (also abbreviated ITC).

Structure of ITC[]

The 12 zodiac signs are widely used worldwide, but the periods of the 12 zodiacs vary between tropical and sidereal astrology. The span of each sign varies from 29 days to 32 days. The span of the month (sign) varies from year to year. So the fixed tropical calendar is needed.

In this ITC, the first 5 months have 31 days each and the remaining 7 months have 30 days each. In leap years, the leap day is added at the end of the year. The details of ITC calendar is given in the following table.

International Tropical Calendar (ITC)
No. Month Code Starting date in Gregorian Calendar Days
01 Aries ARI Mar 21 31
02 Taurus TAU Apr 21 31
03 Gemini GEM May 22 31
04 Cancer CAN June 22 31
05 Leo LEO July 23 31
06 Virgo VIR August 23 30
07 Libra LIB September 22 30
08 Scorpio SCO October 22 30
09 Sagittarius SAG November 21 30
10 Capricorn CAP December 21 30
11 Aquarius AQU January 20 30
12 Pisces PIS February 19 30/31*

Conversion Chart from Gregorian to ITC[]

Month No 1 2 3 4 5 6 7 8 9 10 11 12 12 In Leap
Month Name ARI TAU GEM CAN LEO VIR LIB SCO SAG CAP AQU PIS PIS
Greg Month Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Feb
1 21 21 22 22 23 23 22 22 21 21 20 19 19
2 22 22 23 23 24 24 23 23 22 22 21 20 20
3 23 23 24 24 25 25 24 24 23 23 22 21 21
4 24 24 25 25 26 26 25 25 24 24 23 22 22
5 25 25 26 26 27 27 26 26 25 25 24 23 23
6 26 26 27 27 28 28 27 27 26 26 25 24 24
7 27 27 28 28 29 29 28 28 27 27 26 25 25
8 28 28 29 29 30 30 29 29 28 28 27 26 26
9 29 29 30 30 31 31 30 30 29 29 28 27 27
10 30 30 31 1 1 1 1 31 30 30 29 28 28
11 31 1 1 2 2 2 2 1 1 31 30 1 29
12 1 2 2 3 3 3 3 2 2 1 31 2 1
13 2 3 3 4 4 4 4 3 3 2 1 3 2
14 3 4 4 5 5 5 5 4 4 3 2 4 3
15 4 5 5 6 6 6 6 5 5 4 3 5 4
16 5 6 6 7 7 7 7 6 6 5 4 6 5
17 6 7 7 8 8 8 8 7 7 6 5 7 6
18 7 8 8 9 9 9 9 8 8 7 6 8 7
19 8 9 9 10 10 10 10 9 9 8 7 9 8
20 9 10 10 11 11 11 11 10 10 9 8 10 9
21 10 11 11 12 12 12 12 11 11 10 9 11 10
22 11 12 12 13 13 13 13 12 12 11 10 12 11
23 12 13 13 14 14 14 14 13 13 12 11 13 12
24 13 14 14 15 15 15 15 14 14 13 12 14 13
25 14 15 15 16 16 16 16 15 15 14 13 15 14
26 15 16 16 17 17 17 17 16 16 15 14 16 15
27 16 17 17 18 18 18 18 17 17 16 15 17 16
28 17 18 18 19 19 19 19 18 18 17 16 18 17
29 18 19 19 20 20 20 20 19 19 18 17 19 18
30 19 20 20 21 21 21 21 20 20 19 18 20 19
31 20 21 21 22 22 20
Greg Month Apr May Jun Jul Aug Sep Oct Oct Dec Jan Feb Mar Mar

Date notation[]

The year of ITC is taken from the Kaliyuga Era (3102 BC) which is followed by Hindu people. We calculated the year as follows.

Kaliyuga Era = Common Era + 3100 (before March 21)
Kaliyuga Era = Common Era + 3101 (on or after March 21)

Years within the Kaliyuga Era, i.e. after the epoch, are denoted with KY (Kali Yuga, Kali Year) and years before the Kaliyuga Era are denoted with BKY (Before Kali Yuga). For instance, 2025 CE is 5127 KY.

Let Year is yyyy, month code is MMM, day of the month is DD, the date format is:

KY[yyyy]/MMM/DD

For Example, the date of Gregorian 21 March 2025 has the ITC date: KY5126/ARI/01.

ITC Vs INC[]

Indian National Calendar (Saka) is the another fixed tropical calendar which is permanently synchronized with Gregorian calendar. It starts from March 22 in Normal year, March 21 in Leap year. Total days in this month is 30 in Normal year and 31 in Leap year. But, In ITC, the leap day is added in last month. 51 days (March-31, April 20) are changed from normal to leap year. In ITC, There are only 20 days are changed from Normal year to leap year.

ITC Vs INC
Month No Starting Gregorian Date (INC) Total Days (INC) Starting Gregorian Date (ITC) Total Days (ITC)
1 Mar 22/21* 30/31* Mar 21 31
2 Apr 21 31 Apr 21 31
3 May 22 31 May 22 31
4 Jun 22 31 Jun 22 31
5 Jul 23 31 Jul 23 31
6 Aug 23 31 Aug 23 30
7 Sep 23 30 Sep 22 30
8 Oct 23 30 Oct 22 30
9 Nov 22 30 Nov 21 30
10 Dec 22 30 Dec 21 30
11 Jan 21 30 Jan 20 30
12 Feb 20 30 Feb 19 30/31*

ITC Vs Persian[]

Persian/Iranian Calendar (Solar Hijiri Calendar) is the another fixed tropical calendar which is permanently synchronized with Gregorian calendar. Both calendar starts in March 21 and leap day is added in last month. 6th month of iranian calendar is 31 days, whereas in ITC, it is 30 days. Last month in Iranian calendar is 29 in normal and 30 in leap, whereas in ITC, 30 in normal year and 31 in leap year.

ITC Vs Persian
Month No Starting Gregorian Date (P) Total Days (P) Starting Gregorian Date (ITC) Total Days (ITC)
1 Mar 21 31 Mar 21 31
2 Apr 21 31 Apr 21 31
3 May 22 31 May 22 31
4 Jun 22 31 Jun 22 31
5 Jul 23 31 Jul 23 31
6 Aug 23 31 Aug 23 30
7 Sep 23 30 Sep 22 30
8 Oct 23 30 Oct 22 30
9 Nov 22 30 Nov 21 30
10 Dec 22 30 Dec 21 30
11 Jan 21 30 Jan 20 30
12 Feb 20 29/30* Feb 19 30/31*

Equinox and Solstices[]

In Equinox, the span of Day and Night is absolutely equal, where the sun rays are perpendicular to the equator of Earth. These are two types, Northward Equinox (Spring/Vernal Equinox) and Southward Equinox (Autumn Equinox). The span of day (North hemisphere) is larger when sun rays are perpendicular to 23 1/2 degree of earth which is referred as Tropic of Cancer on Summer Solstice. Similarly, The span of Night (North hemisphere) is larger when sun rays are perpendicular to 23 1/2 degree of earth which is referred as Tropic of Capricorn on Winter Solstice. The seasons are perfectly fixed in ITC.

In 2025,

  1. Vernal Equinox - 2025 March 20 (5125 Pis 30) 2:31 PM IST
  2. Summer Solstice - 2025 June 21 (5126 Gem 31) 8:11 AM IST
  3. Autumn Equinox - 2025 Sep 22 (5126 Lib 1) 11:49 PM IST
  4. Winter Solstice - 2025 Dec 21 (5126 Cap 1) 8:32 PM IST

Name of Quarters/Seasons[]

Quarters
Q.No Months Name Name Name
1 Aries, Taurus, Gemini ATG Arini Artge
2 Cancer, Leo, Virgo CLV Cango Calvi
3 Libra, Scorpio, Sagittarius LSS Libus Lissa
4 Capcricorn, Aquarius, Pisces CAP Capes Caapi

Features[]

  1. The dates are permanently fixed to Gregorian Calendar. Only 20 dates differ in a leap year, i.e. 1–20 March.
  2. Precession is approximated as follows:
    1. Spring Equinox - Aries 01 (Mar 21)
    2. Summer Solstice - Cancer 01 (June 22)
    3. Autumn Equinox - Libra 01 (Sep 22)
    4. Winter Solstice - Capricorn 01 (
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