Solar and lunar months: what changes?
A solar month follows the Sun through a sign; a lunar month counts 30 tithis, so the two measures need not begin together.
STEP 1
Solar month: one sign
In this traditional measure, a solar month runs from the Sun's entry into one 30-degree sign to its entry into the next. At 15° within a sign, another 15° remains before that next entry. This is angular distance, not a count of days.
STEP 2
Lunar month: thirty tithis
A lunar month contains 30 tithis. Each tithi covers a 12-degree increase in the Moon's lead over the Sun. Because this measures changing positions rather than midnight boundaries, 30 tithis do not mean 30 civil dates.
STEP 3
Recognize a lunar-month name
Names such as Kartika have traditional associations with nakshatras, or lunar divisions. Kartika is associated with Krittika. The name alone does not specify the Moon's exact nakshatra on a particular date; read the calendar's separate nakshatra entry for that.
STEP 4
Read the headings together
Compare a solar-month heading tied to Aries (Mesha) with a lunar-month heading such as Kartika. Ask what each is counting. Then check whether the numbers underneath are calendar dates or tithis, and note any stated convention for when the month starts.