month

month

1. one of the twelve divisions (calendar months) of the calendar year

2. the period of time (tropical month) taken by the moon to return to the same longitude after one complete revolution around the earth; 27.321 58 days (approximately 27 days, 7 hours, 43 minutes, 4.5 seconds)

3. the period of time (sidereal month) taken by the moon to make one complete revolution around the earth, measured between two successive conjunctions with a distant star; 27.321 66 days (approximately 27 days, 7 hours, 43 minutes, 11 seconds)

4. the period of time (lunar or synodic month) taken by the moon to make one complete revolution around the earth, measured between two successive new moons; 29.530 59 days (approximately 29 days, 12 hours, 44 minutes, 3 seconds)

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Month

month

The period of the Moon's revolution around the Earth with reference to some specified point in the sky (see table). The differences in the monthly periods result from the complicated motion of the moon.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

month

[mənth]

(astronomy)

The period of the revolution of the moon around the earth (sidereal month).

The period of the phases of the moon (synodic month).

The month of the calendar (calendar month).

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Month

 

an interval of time nearly equal to the period of revolution of the moon about the earth. Different types of months are distinguished (see Table 1 and Figure 1). These include (1) the synodic month, which is the period of the sequence of the lunar phases (it serves as the basis for lunar calendars);

Table 1. Length of various types of months
Type of month	Mean solar days	Mean solar time
Synodic .....	29.530588	29 days	12 hr	44 min	3 sec
Sidereal .....	27.321661	27 days	7 hr	43 min	12 sec
Tropical .....	27.321582	27 days	7 hr	43 min	4 sec
Anomalistic .....	27.554550	27 days	13 hr	18 min	33 sec
Nodical .....	27.212220	27 days	5 hr	5 min	36 sec

(2) the sidereal month, during which the moon performs a complete revolution about the earth and returns to its original position relative to the stars; (3) the tropical month, which is the period during which the moon returns to a given longitude; (4) the anomalistic month, which is the interval of time between successive passages of the moon through the perigee; and (5) the nodical month, which is the period of time between successive passages of the moon through the same node of its orbit (this concept is important for the theory of eclipses). In the Gregorian calendar, the year is divided into 12 months, each month containing from 28 to 31 days; this calendar does not agree with the lunar phases.

Figure 1. Difference between synodic and sidereal months. (1) and (3) are the relative posiositions of the sun, earth, and moon at which a full moonon occurs (a time interval of oneone synodic month); (2) is the position of the moon after a complete revolution about the earth (a time interval of one siderealreal month).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.