सिद्धान्तदर्पण (महामहोपाध्याय सामन्त चन्द्रशेखर सिंह - नग्न-नेत्र खगोल वेध एवं गणित महाकोश)

Introduction xxxiii
150 years B.C. It is an irregularity which may put
the Moon forward or backward over a degree.
Pandit Sudhakar Dwivedi informs us in his excellent
manual, called Ganaka-Tarangini, that Munjala
(A.D.933) had something like "’evecation’ in his
karana named Laghumanasa. He appears to have
been the oldest Hindu astronomer who detected the
irregularity, through curiously enough, his
successors including Bhaskara left it unnoticed.
The next large irregularity of the Moon, called
"variation," has a period of one month, and a
maximum of 39'31". This inequality does not affect
the time of an eclipse, and the fact sufficiently
explains its absence in Sanskrit Siddhantas.¹ It is
said to have been detected by an Arbian astronomer,
Aboul Wefa about the year 975 A.D., and re-
discovered by Tycho Brahe in the 16th century. The
last large inequality of the Moon's place is called
"annual equation," and has the maximum amount of
11'9". This was also discovered by Tycho Brahe.
It is singular that Chandrasekhara is the only
Indian astronomer who has detected all the three
important irregularities of the Moon. As has been
said before, he did not know English and had not
means of knowing of the existence of the
irregularities from any foreign source; and the
methods of applying the corrections together with
discrepancies between his values and those of
Europe leave no doubt in our mind that he must
be credited with their discovery. He has named the

1. From Dwivedi’s Ganaka-tarangini, it appears that
   Nityananda in 1639 A.D. used a correction called
   Pakshika. But it is not clear from the name alone, if it
   had any connection with "variation".