The Local Mean Time

The time elapsed from the midnight of the place is  known as local mean time. Thus L M T at midnight is  zero hours. This is different from the hour-angle of the mean Sun. The Earth is rotating from the west to east and it completes one rotation with respect to the Sun in one civil day. However, it completes one complete rotation with reference to any distant star in one sidereal day.  Its  spin in a sidereal day is 360°, while the same is about 361° for a civil … Continue reading

Mean Solar Day

We have seen that the Sun appears to describe an elliptical orbit around the Earth and its rate of change of direction in the orbit is not constant, i.e. the Sun appears to move somewhat non-uniformly in the zodiac. It moves faster when the Earth is at its perihelion, i.e. the nearest point from the Sun. Conversely the angular speed is slowest when the Earth is at aphelion point (the farthest from the Sun). The other factor is that the Sun appears to move in the ecliptic and not in … Continue reading


The planets are called combust when they are near the Sun in longitudes and their rays which are the reflection of the Sun’s rays are intermingled with that of the Sun whose rays are much stronger. Therefor, the effect of the planets becomes much less. I ‘he planet under combustion is not visible, being too near the Sun, and is called A sta. Continue reading


Moon’s sidereal period of revolution is about 277, days and it moves eastwards with reference to the  stars and at an average of more than half a degree per hour. In its movement, it continually interposes  its  disc between us and the stars. The sudden disappearance of a star by the Moon’s disc is caslled  the occultation of the star by the Moon. Actually, the covering up of one celestial body by mother is generally called occultation. Strictly peaking, the- solar eclipse is also an occultation of the Sun by … Continue reading


The solar eclipse will occur when the Moon is in between the Earth and the Sun i.e. (1) It will be an amavasya. (2) The Moon must be on or near Rahu or Ketu so that its latitude is near zero and the three heavenly bodies, the Moon, the Earth and the Sun, are in a line. The reasons for a solar eclipse are the same as for lunar eclipse i.e. the Sunrays should be stopped by the dark (non-luminous) Moon from falling on the Earth. It can happen only … Continue reading


A lunar eclipse takes place when the Moon passes through the shadow of the Earth in the heavens. This will only occur when all the three i.e. the Sun, the Earth and the Moon are nearly in a straight line. The Sun and the Earth are always on the ecliptic but the path of the Moon is inclined to the ecliptic at an angle of about 5°. So the Moon may or may not be on or very near the ecliptic when the Earth is in between the Sun and … Continue reading


The Sun is the only illuminated heavenly body which is actually a star in the solar system and Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto are its planets, reflecting the light received from it. All the planets are revolving around the Sun as already explained in chapter 3. The Earth is moving around the Sun under the gravitational pull of the Sun. The Moon is moving around the Earth and along with the Earth, it goes around the Sun also, under the gravitational pull of the Earth. … Continue reading


Synodic  period is the interval of time which   elapses  between two oppositions or two conjunctions of a superior planet. In case of inner-planets it is the time  between two conjuntions of the same type whether  they are both inferior or superior. It can be explained as under: The  Sun is stationary. The planets (including the  Earth ) are revolving around it. The earth completes one revolution in approximately 365 days while Mercury com pletes it in 88days. In the figure 16, let E be the  Earth, M, Mercury and S, Sun. EMS is the … Continue reading


Time, includingsidereal time, can be measured in many ways. Sidereal day is the time elapsed since the precedding transit of Sayana first point of Aries to the next transit of the meridian of a place. In other words, one sidereal day is the time taken by the Earth in completing one rotation with respect to a fixed star which is equal to 23 hours 56 minutes and a few seconds. This sidereal day is expressed in sidereal hours and minutes. One sidereal day is equal to 24 sidereal hours. One such … Continue reading


Sidereal period or periodic time of a planet is the time taken by it to make a complete revolution with reference to the fixed stars. In the case of the Moon it is 27 days 7 hours and 43 minutes. This is the minimum sidereal period among nava  grahas. The maximum sidereal period is that of Saturn which is 29.46 solar years. After considering the extra Saturnine planets, the maximum sidereal period is that of Pluto i.e. 248.4 years. Continue reading