Kalaprakasika (1917, p. 175) divides the daytime into eight periods. The day's own lord takes the first, and the other weekday lords follow in weekday order. Four periods have names: Gulika is Saturn's, Yamagandam Jupiter's, Ardhaprahara Mercury's and Kalan the Sun's. The book sets Ardhaprahara, Yamagandam and Kalan aside for good work, and says in a footnote that Gulika is not counted as inauspicious. The app shows Yamagandam and Gulika (with Rahu Kalam); it does not show Ardhaprahara or Kalan.
☕ Eight parts, seven lords
Take the daytime, sunrise to sunset, and cut it into eight equal parts. Give the first part to the lord of the weekday: the Sun on Sunday, the Moon on Monday, and so on. Give the next parts to the next weekday lords in order. Seven lords fill seven parts; Kalaprakasika gives the eighth back to the day's lord, while BPHS leaves it without a lord.
Each named window is then simply one lord's part. Saturn's part is Gulika and Jupiter's is Yamagandam, the two windows almanacs print every day. Kalaprakasika names two more: Mercury's part, Ardhaprahara, and the Sun's part, Kalan. Muhurta Chintamani names the same family by a counting rule and calls Mercury's part Kalbela and Mars's part Kantaka. Reading all four lists as lordship is our arithmetic on the book's tables; it fits every cell.
Rahu Kalam is printed beside them in almanacs, but it is not one of these parts: Rahu is not a weekday lord. It has its own article. The windows series explains Yamagandam and Gulika on their own.
The rule this page explains is the two further eighths Kalaprakasika names, Ardhaprahara and Kalan. Nava Panchangam does not use this rule in its day score. This page explains it as the books give it. The app does not compute Ardhaprahara or Kalan. Separately, it shows Rahu Kalam, Yamagandam and Gulika, dividing the actual daytime by eight, and the day score weighs those three as time windows of its own.
The named periods and the books' notes
- Kalan: the Sun's period
- Ardhaprahara: the Mercury's period
- Yamagandam: the Jupiter's period
- Gulika: the Saturn's period
- Kalaprakasika (p. 176): Ardhaprahara, Yamagandam and Kalan are set aside for good work
- Kalaprakasika (pp. 175, 192): Gulika is not counted as inauspicious, and suits some works
- Muhurta Chintamani: the named window is the second half of the part, half as wide
- Tamil almanacs and the app: the whole part, as Kalaprakasika's plate prints it
Frequently Asked Questions
What is Ardhaprahara?
One of the eight parts of the day, the part that falls to Mercury. Kalaprakasika names it and sets it aside for good work, with Yamagandam and Kalan. Muhurta Chintamani calls the same part Kalbela.
What is Kalan?
The Sun's part of the day: the first part on Sunday, and one part earlier each weekday after that (the 7th on Monday, the 6th on Tuesday). Kalaprakasika lists it with Ardhaprahara and Yamagandam.
Why does the book's table say 6 to 7:30 when my sunrise is not at 6?
Kalaprakasika's plate assumes a 12-hour day from 6 o'clock. The rule itself is eight equal parts of the real day, so on a long summer day each part is longer than an hour and a half. The app divides your actual daytime by eight.
Is Gulika inauspicious?
Kalaprakasika's footnote (p. 175) says Gulika is not counted as inauspicious, and a later page (p. 192) lists works for which it has no ill force. Tamil almanacs print it with Rahu Kalam and Yamagandam, and the app follows the almanac.
Why is Muhurta Chintamani's window shorter?
It splits the day into sixteen muhurtas, two to each part, and names only the second of the two. So its window is half as wide, on the same part. Kalaprakasika's plate and the Tamil almanac use the whole part; so does the app.
From the sources
The book's day and night tables, read as lordship, and where Muhurta Chintamani differs.
☀️ By day
The period number of each named window, with its time on Kalaprakasika's nominal 6-to-6 day (p. 176). Each column is one lord's period, counted from the day's own lord.
| Weekday | Kalan | Ardhaprahara | Yamagandam | Gulika |
|---|---|---|---|---|
| Sunday | 1 (6:00–7:30) | 4 (10:30–12:00) | 5 (12:00–1:30) | 7 (3:00–4:30) |
| Monday | 7 (3:00–4:30) | 3 (9:00–10:30) | 4 (10:30–12:00) | 6 (1:30–3:00) |
| Tuesday | 6 (1:30–3:00) | 2 (7:30–9:00) | 3 (9:00–10:30) | 5 (12:00–1:30) |
| Wednesday | 5 (12:00–1:30) | 1 (6:00–7:30) | 2 (7:30–9:00) | 4 (10:30–12:00) |
| Thursday | 4 (10:30–12:00) | 7 (3:00–4:30) | 1 (6:00–7:30) | 3 (9:00–10:30) |
| Friday | 3 (9:00–10:30) | 6 (1:30–3:00) | 7 (3:00–4:30) | 2 (7:30–9:00) |
| Saturday | 2 (7:30–9:00) | 5 (12:00–1:30) | 6 (1:30–3:00) | 1 (6:00–7:30) |
🌙 By night
Kalaprakasika's plate (p. 176) gives the night too, from 6 in the evening. The night's count starts from the lord of the fifth weekday counted from the day: Sunday night starts from Thursday's lord, Jupiter. Read that way, the four night columns are the same four lords.
| Weekday | Kalan | Ardhaprahara | Yamagandam | Gulika |
|---|---|---|---|---|
| Sunday | 4 (10:30–12:00) | 7 (3:00–4:30) | 1 (6:00–7:30) | 3 (9:00–10:30) |
| Monday | 3 (9:00–10:30) | 6 (1:30–3:00) | 7 (3:00–4:30) | 2 (7:30–9:00) |
| Tuesday | 2 (7:30–9:00) | 5 (12:00–1:30) | 6 (1:30–3:00) | 1 (6:00–7:30) |
| Wednesday | 1 (6:00–7:30) | 4 (10:30–12:00) | 5 (12:00–1:30) | 7 (3:00–4:30) |
| Thursday | 7 (3:00–4:30) | 3 (9:00–10:30) | 4 (10:30–12:00) | 6 (1:30–3:00) |
| Friday | 6 (1:30–3:00) | 2 (7:30–9:00) | 3 (9:00–10:30) | 5 (12:00–1:30) |
| Saturday | 5 (12:00–1:30) | 1 (6:00–7:30) | 2 (7:30–9:00) | 4 (10:30–12:00) |
📖 Where the books differ
Muhurta Chintamani finds the part by counting from the day to a fixed weekday (to Saturday for Kulika, to Thursday for Yamaghanta) and lands on the same part. But it names only the second half of that part, so its window is half as wide. The app keeps the whole part, as Kalaprakasika's plate and the Tamil almanac do.
The two windows the app shows: Yamagandam and Gulika Kalam; and the separate Rahu Kalam.