The Motions of the Planets and the Retrograde Effect

When seen from the perspective of an astrological horoscope, the Geo Centric theme acts as the key reference point. It is based on the assumption of keeping the apparent reference of Earth as the center point with all the planets revolving around it. Thus it is important to know the effect of how different planets affect while transitioning around the zodiac signs based upon keeping Earth as the base. However in reality as per the onus of the solar system it's always the planets circulating around the sun in the order of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. 

As Earth is taken as the base, we generally consider Mercury and Venus as inner planets whereas Mars, Jupiter and Saturn are considered as outer planets to the Earth's orbit. Uranus, Neptune and Pluto which are much further away are not considered within the parlance of Vedic Astrology but in essence they also need to be seen as outer planets. The Sun and the Moon which is revolving around the Earth are considered as the luminaries emitting source of light and have a significant role to play in the charter of a horoscope. They signify the soul and the mind respectively and play a crucial role in the decoding of a horoscope. In fact the Ascendant sign (the sign rising in the Eastern Horizon when an individual takes birth / event takes place), the Sun sign and the Moon sign are considered as the Big 3 in a horoscope and are extremely essential in deriving a number of areas to study within a horoscope. Their use both as individual points as well as a reference point based on which other planetary configurations are studied can exhibit wide avenues of analysis within the purview of a horoscope.

Daily Motion of Planets
Let's go about ascertaining the average motion of planets viewed in from the Earth's geo centric perspective. Though they all revolve around the Sun, we consider the center of the Earth as the base point and determine the movement travelled by the various planets when circulating around the Sun in the solar system. Please do note this is more or less the average daily speed whereas actual speeds can vary on a given day, depending on when a planet turns stationary and moves between direct and retrograde motion. Also listing down the highest and lowest daily speeds for those available cases. 

Sun
Average Speed : 00°59'08"
Highest Speed :  01°03'00"
Lowest Speed :  00°57'10"

Moon
Average Speed : 13°10'35"
Highest Speed : 16°30'00"
Lowest Speed :  11°45'36"

Mars
Average Speed :  00°31'27"
Highest Speed :   00°52'00"
Lowest Speed : −00°26'12"

Mercury
Average Speed :  01°23'00"
Highest Speed :   02°25'00"
Lowest Speed : −01°30'00"

Jupiter
Average Speed :  00°04'59"
Highest Speed :  00°15'40"
Lowest Speed : −00°08'50"

Venus
Average Speed :  01°12'00"
Highest Speed :  01°22'00"
Lowest Speed : −00°41'12"

Saturn
Average Speed :  00°02'01"
Highest Speed :  08°48'00"
Lowest Speed : −00°05'30"

Though planets further than Saturn are considered within the purview of Vedic Astrology, documenting below the speeds of the planets much further from the Earth such as Uranus, Neptune and Pluto for the purpose of reference

Uranus
Average Speed :  00°00'42"
Highest Speed :  00°04'00"
Lowest Speed : −00°02'40"

Neptune
Average Speed :  00°00'24"
Highest Speed :  00°02'25"
Lowest Speed : −00°01'45"

Pluto
Average Speed :  00°00'15"
Highest Speed :  00°02'30"
Lowest Speed : −00°01'48"

When it comes to the nodes Rahu and Ketu, they normally transit in a reverse direction as seen from the Earth's parlance and their average daily motion is documented below:

Rahu
Average Speed :  −00°03'00"

Ketu
Average Speed :  −00°03'00"

For the purpose of a horoscope, the Ascendant plays a massively important role and this is deduced based on Earth's own rotation around it's axis which approximately takes about 23 hours 56 minutes and 4.09 seconds to cover the full span of 360°. Hence on an average day of 24 hours we can say that the Earth rotates 360° plus about an additional degree for the remaining about 4 minutes after completing one full rotation

Earth (For Ascendant)
Average Speed : 361°00'00"

Speed Order of Planets
Thus, when looked at the speed order, we can easily decipher that the Ascendant is the fastest being able to cover the entire paradigm of 360° covering all the zodiac signs in a day. This is followed by the Moon which covers on an average an entire Nakshatra span of 13°20'00". It covers the entire 27 Nakshatras spread across the 12 zodiac signs in just a little over 27 days. These are followed by the monthly planets viz Mercury, Venus and Sun all of which transit a zodiac sign in about a month's time. Then it is followed by the bi-monthly planet Mars which roughly transits a sign around once every two odd months. After this comes Jupiter which approximately transits in a zodiac sign for a period of a year. Then comes the nodes Rahu & Ketu which stay in a sign for roughly a year and a half and finally rounding up is Saturn which transits in a zodiac sign for a period of 2 and half years. One of the pertinent reasons why the planets Uranus, Neptune and Pluto are eliminated from the ambit of Vedic Astrology could be the fact that they take a very long time to complete a full round of the zodiac with these planets approximately taking about 84 years, 148 years and 236 years to complete one full cycle. That could be a potential reason as to why the impact may not be of much significance when seen from an individual horoscope as their transit time is exceedingly large.

Retrograde Motion
While studying the motion of planets, it is extremely prudent to also take into account the phenomena of the retrograde effect. Retrograde may mean moving backwards but in essence the planets don't really head backwards while revolving around the Sun in the solar system. But since we are looking at the movement of planets from the Earth's perspective, certain planets appear to be going backwards causing this phenomena. It in fact needs to be titled to as apparent retrograde motion since it's factored from the Earth's angle. The most widely used example of understanding this phenomena is by considering 2 parallel trains. For those placed in the faster train, it gives an illusory appearance of the slower train moving backwards and going in the opposite direction but in essence that's not the case and it is only moving slowly. This happens when the planets revolve around the Sun and undergo velocity changes at different paths in it's movement.

When considering Vedic Astrology, the Sun and Moon only move in the forward direction and do ever come into the picture of getting retrograde. The Rahu and Ketu almost always go in the reverse direction and hence they more or less always tend to be retrograde. Rahu and Ketu are mathematical pointers that arise when the orbit of the Moon cuts the ecliptic. True nodes tend to wobble around a bit causing some tilt in the opposite direction whereas Mean nodes always only tend to be retrograde as it's averaged out and calculated at a constant speed. For all practical purposes, we can safely consider Rahu & Ketu to be in retrograde motion most of the time. When it comes to the other 5 planets mainly in Vedic Astrology, we can split them as inner planets to Earth comprising of Mercury & Venus and the outer planets to the earth consisting of Mars, Jupiter and Saturn. These planets tend to go retrograde at different times based on their varying velocity while orbiting in the solar system. This is the reason you would associate a negative sign when marking the slowest speed of these planets.

Types of Motions
As per the Geo - centric model, these 5 planets undergo 8 types of movement which are as below:

Direct Motion:

1) Manda - Direct and quickening or constant daily motion but somewhat slow moving

2) Mandatara - Direct and slowing or constant daily motion but very slow moving

3) Shiigra or Chara - Direct and slowing or constant daily motion but fast moving

4) Shiigratara or Atichara - Direct and quickening or constant daily motion but very fast moving

5) Kutila or Vikala - Planet is in a stationary motion which equates to defective/deficient motion

6) Sama - Direct and even comprising of smooth constant motion

Retrograde Motion:

7) Vakra - Moving backward quickly relative to its attainable daily daily speed

8) Anuvakra - Moving backward slowly relative to its attainable daily daily speed

The sequence of planets getting retrograde happen based on the following order:

- Kutila or Vikala - Planets are stationery

- Manda - Planets slow down but are in direct and quickening motion

- Sama - Planets are direct and in even motion

- Shiigratara or Atichara - Planets are in direct and quickening motion, or constant but fast

- Sama - Planets are in direct and even motion

- Shiigra or Chara - Planets are in direct and slowing motion, or constant but fast

- Mandatara - Plantets are direct and slowing, or constant but slow

- Kutila or Vikala - Planets are stationery

- Anu Vakra - Planets are retrograde but slow

- Vakra - Planets are retrograde but fast

- Anu Vakra - Planets are retrograde but slow

- Kutila - Planets become stationery again

Retrograde in Horoscope 

Planets as we have seen become retrograde due to the relative speed undergoing a change during their motion in orbiting the Sun as seen from the lens of the Earth. Thus, planets in retrograde are generally said to be closer to the Earth and further off from the Sun. This holds especially true for the outer planets Mars, Jupiter and Saturn and we tend to manually ascertain if a planet is retrograde just by seeing how many houses it's moved away from the Sun. When it comes to Venus & Mercury, they always tail gate with the Sun and this doesn't really hold true of it being farther off from the Sun and closer to Earth. Mercury and Venus becomes retrograde when it appears to move backward as seen from the planet Earth. Generally when Mars, Jupiter and Saturn are placed in the 5th, 6th, 7th, 8th and 9th houses from the Sun they tend to get retrograde with Mars being retrograde when placed approximately 140° from the Sun, Jupiter about 115° from the Sun and Saturn about 110° from the Sun.

Listed below are the approximate days in which the planets become retrograde:

Mercury - It takes approximately 88 days to orbit around the Sun. Goes into retrograde motion about 3 to 4 times in a year and lasts roughly for around 24 days (3-4 weeks)

Venus - It takes approximately 225 days to orbit around the Sun. Goes into retrograde motion once in about 18 months and lasts roughly for around 50 days (7 weeks)

Mars - It takes approximately 687 days to orbit around the Sun. Goes into retrograde motion once in about 26 months and lasts roughly for around 74 days (2.5 months)

Jupiter - It takes approximately 4333 days to orbit around the Sun. Goes into retrograde motion once in about 9 months and lasts roughly for around 122 days (4 months)

Saturn - It takes approximately 10756 days to orbit around the Sun. Goes into retrograde motion once in about a year and lasts roughly for around 140 days (4.5 to 5 months)

Vedic Astrology Perspective of Retrograde Planets

As per Vedic Astrology, planets in Retrograde mention are said to get Chesta Bala as per the six fold Shad Bala calculation in ascertaining strength of planets. Thus if the planets are in retrograde motion, they are said to be strong and powerful. When it comes to results, Retrograde can be loosely translated as crooked (Vakri) and these planets can tend to give results much against their usual nature. It can work two ways and thus expected beneficial attainment can turn into negative attainment and vice versa. Working with Retrograde planets can be a little bit tricky as it's not really easy to judge their results but however it needs to be remembered always that planets in retrograde motion are much stronger than when they are in direct motion.

The Earth Centric Model and the Latitude Longitude Coordinates

A point of reference plays a very vital role within the ambit of a horoscope. When measuring distances or ascertaining directions, we always assimilate the same based on a central point and do the evaluation. Likewise when viewing the position of planets in the sky, it is imperative to know where they are located and their co-ordinates from a particular reference point. Without a reference object, it wouldn't really matter how further they are positioned in the sky or make any sense as to the impact effected by them. 

In the parlance of a horoscope, it is always the Earth which acts as the central pivot based on which planetary longitudes and latitudes are computed and the impact caused by them based on their placement in different signs and houses. This is in effect the main reason we do not see the 'Earth' being marked in any horoscope is because it's always from the Earth that the effect of other planets are deduced. If of course one wants to know the position of Earth, it would be located exactly 180 degrees from the Sun's position in a particular horoscope.

Reference Centric Models 

There are different theories and models circulated for estimating the position of planets from a particular reference point. Lets briefly look at the different reference centric models

- Geocentric Model
This is an Earth centric model. As per this model, it is assumed that earth is at the center of the universe and all the planets including the Sun revolve around it. In this model, geo centric positions are calculated with respect to the center of the earth. Geo is alternatively used as a term to describe Earth.

- Topocentric Model

This is an Earth centric model. In this model also, it is assumed that earth is at the center of the universe and all the planets including the Sun revolves around it. However in this model, the positions of planets including Sun are calculated with respect to the observers location which can be the actual place of birth of an individual or at the epicentre of where an event has taken place.

- Heliocentric Model

This is a Sun centric model. In this model, it is assumed that the Sun is at the center of the universe and all the other planets including the Earth revolves around it. Helios is another name for Sun and hence appropriately named so.

- Planetocentric Model

This is a planet centric model. In this model, a particular planet is assumed as the reference point with other planets including the Earth and Sun revolving around it. This is mostly adopted with the planet Mars being the source of reference and deducing the position of all other planets including Sun and Earth.

- Barycentric Model

This is a solar system centric model. Barycenter is defined as the center of a mass. In this model, a point in the solar system is considered as the reference and establishes the coordinates of all the other planets including Sun and Earth. 

There has been a perennial debate whether its the Earth that revolves around the Sun or whether it's the Sun that revolves around the Earth. Astronomers after numerous research and evidence have finally concluded that it's the latter which holds true. Hence the real picture that takes place in the skies is the Heliocentric model where all planets including the Earth revolves around the Sun.

However we cannot overlook the fact that human beings are born on earth and major events take place on Earth. So it is prudent and makes extra sense to view it with reference to the point of view of Earth. Planetocentric and Barycentric models are basically documented for academic purposes and Heliocentric though it accounts for the real perspective of keeping Sun at the center, it doesn't hold ground at least from an horoscopic angle as all things concerned are looked at with respect to the Earth as the base point.  

Thus, while looking at it from a horoscope standpoint, it is the Geocentric or Topocentric model which is used when computing planetary coordinates. In all the astrology software's and even almanacs, it is the Geocentric position that is used at vogue which is the methodology of accounting for planetary coordinates keeping the center of the Earth as the base point. The center of the Earth falls at the Royal Observatory in Greenwich, United Kingdom which falls at a longitude of 0 degrees. Greenwich was universally chosen to be the Prime Meridien of the World in 1884. The Royal Observatory is the source of the Prime Meridian of the world with Longitude of 0° 0' 0''. The prime meridian marks the divide between the eastern and western hemispheres.

Thus irrespective of where one takes birth whether it happens to be east of Greenwich say India or the western side of Greenwich say United States, planetary coordinates will not differ as they are all determined using Greenwich as the central reference point. However there is one important position in a horoscope which is used as the starting reference point known as the Ascendant and this is obtained as the point that is rising on the eastern horizon based on the observers location. Hence lets say person A was born in India at 3PM and person B is born in the United States also at 3PM. Though the planetary positions will remain more or less the same as in both cases as they are determined using Greenwich as the central location, however the Ascendant will undergo a change as the point rising in the Eastern horizon in India will be different from that of the United States. The House counting system is usually done by taking the Ascendant as the base and this will have a major say in the referencing of a Horoscope.

Also one of the major basis for the Geocentric system is that all planetary positions need to be calculated based on a fixed reference point on Earth and it's center position happens to be the only fixed point on the Earth's surface. If we take any other point based on observer's location, it cannot hold to be a fixed common point as the Earth's surface is always moving due to it's rotational movement around it's axis. Planetary coordinates don't really change taking either of Geocentric or Topocentric positions sans the Moon alone. In the case of the Moon, there tends to be a difference by about a degree and this can change the outcome of a horoscope in a major way. The deviation tends to be maximum when Moon is placed near to the Ascendant or in the opposite 7th house and is minimum when positioned near to the 4th or 10th house. Moon's position is especially used while computing Dasa Balance at birth and this could alter proceedings in a major way. However the general norm is that Moon's position is also calculated based on Geocentric position since Moon revolves around the center of the Earth and not just any point on the Earth's surface. However this point should be kept in mind in determining the analysis of a horoscope since it can end up having quite a major impact.

When it comes to determining the Ascendant, it is important to reference the latitude and longitude of the place on earth where an individual is born or an event has taken place. The Latitude and Longitudes combine to form grids which are key for locating places on the earth and arriving at the coordinate position. These are certain imaginary lines drawn on the earth that enables to precisely decode selective places located on planet Earth. The Earth as such is defined as a 'Geoid' meaning that it is slightly flattened at the North & South pole and bulged in the middle. This makes the earth's equatorial diameter as 12756 kms (West to East) whereas it's polar diameter is 12714 kms (North to South). Let's look at a few important snippets with respect to the imaginary lines that are drawn on the earth namely the Latitude and Longitude.

Latitudes:

- Latitudes also called 'Parallels' are horizontal lines that run from the West to the East across the Earth

- The most important Latitude line is the Equator which divides the Earth equally into two halves viz the Northern Hemisphere and the Southern Hemisphere

- The Northern most point of the Earth is termed as the North Pole and the Southern most point of the Earth is called as the South Pole. The lines drawn above the equator are called North Latitudes and lines below the equator are called South Latitudes. It should however be noted that the Latitude lines are not of equal length.

- Latitudes measure the distances in degrees starting with the equator at 0 degrees. They go up the equator marked from 1 to 90 degrees all the way to the North Pole and likewise go down the equator marked from -1 to -90 degrees all the way to the South Pole. The numbers in positive indicate that they are part of the Northern Hemisphere and the numbers in negative indicate they belong to the Southern Hemisphere. Alternatively they can also be coded with the acronym as North and South. Eg +30 degrees in North can be written as 30°N and -30 degrees in South can be denoted as 30°S.

- The other important Latitude lines are the Tropic of Cancer & Arctic Circle located in the Northern Hemisphere and the Tropic of Capricorn & Antarctic Circle located in the Southern Hemisphere. These help to define climatic zones based on the different quotients of sunlight received throughout the year. The Tropic of Cancer is at 23° 26' N and the Arctic Circle is at 66° 34' N whereas the Tropic of Capricorn is at 23° 26' S and the Arctic Circle is at 66° 34' S. Generally they are stated as being 23 and a half and 66 and a half degrees North and South respectively.

- The portion from Equator to Tropic of Cancer in the Northern Hemisphere and Equator to Tropic of Capricorn in the Southern Hemisphere are called 'Torrid Zones'. This is the place where maximum sunlight gets received. The portion from the Tropic of Cancer to Arctic Circle in Northern Hemisphere and from Tropic of Capricorn to Antarctic Circle in Southern Hemisphere are termed 'Temperate Zones'.They are of moderate climate and experience 4 different seasons. The portion from Arctic Circle to the North Pole in Northern Hemisphere and between the Antarctic Circle to the South Pole in Southern Hemisphere is known as the 'Frigid Zone'. These usually experience cold climate as they are placed in an angle that receives very less sunlight.

Longitudes:

- Longitudes also called 'Meridians' are vertical lines that run from the North to the South across the Earth

- The most important Longitude line is the Prime Meridian which divides the Earth equally into two halves viz the Western Hemisphere and the Eastern Hemisphere

- Longitudes measure the distances in degrees starting with the Prime Meridien at 0 degrees. The lines to the right of the Prime Meridian are marked from 1 to 180 degrees all the way to the East and the lines to the left of the Prime Meridian are marked from -1 to -180 degrees all the way to the West. The numbers in positive indicate that they are part of the Eastern Hemisphere and the numbers in negative indicate they belong to the Western Hemisphere. Alternatively they can also be coded with the acronym as East and West. Eg +120 degrees in East can be written as 120°E and -120 degrees in West can be denoted as 120°W.

- The lines of the Longitude help in determining time zones across the globe because when it's day in one of the hemispheres, it's night in the other hemisphere and vice versa. It should however be noted that unlike Latitude lines, Longitude lines happen to be of equal length.

- The 0° longitude which passes through Greenwich is considered as the historic Prime Meridian of the World and all the time zones across the globe are calculated with reference to this. The 180° longitude line to the West and East of the Prime Meridien is termed as the Anti Meridian or the International Date Line.

- The Earth rotates 360° in about 24 hours which equates to 15° for every hour and 1° for every 4 minutes. Hence if time at Greenwich is 12 noon, a place that is 15° to the East would be one hour ahead which would equate to 1PM and a place that is 15° to the West would be one hour behind which would be 11AM. This is also the basis for AM and PM which translates as Ante Meridiem and Post Meridiem where AM refers to before midday and PM identifies with after midday. Thus the A.M (or morning time) is the time before the sun passed meridian and P.M (or afternoon time) is the time after the sun has passed meridian at noon

- Based on the lines of longitude , 24 of them have been marked as standard meridians. Taking Prime Meridian as 0° longitude, the longitudes at 15° intervals are known as Standard Meridians. Hence on the East of the Prime Meridian there are 12 time zones and on the West of the Prime Meridian there are another 12 time zones (180° divided by 15° standard)

Time is decided according to movement of the Earth. Based on this different places have day and night occurring at varying time periods. If there were no time zones prevalent and if every place adopted the same universal time, it would be 6AM in one part of the world and fully Sunny and yet be 6AM in another part of the world and be completely dark. It is usually perceived that the dawn of Sun to be a signifier of morning activities and accordingly Sunrise time is adopted as the morning time in different places and the setting of Sun is considered as evening time in different places. As the Earth rotates from West to East, the places East of the Prime Meridien are those that receive the light of the Sun first and those places to the West of the Prime Meridien receive the light much later on. That is the reason you would see places like Australia, New Zealand, Japan etc gaining time compared to places in the United States, Canada etc which are losing time.

Though there are countries with places which are spread across different standard meridians, it's not always the case that different places within a country adopt different time zones. One example being India which universally adopts a Standard Meridian of  82°30' East based on the Meridian line which passes through Prayagraj in Uttar Pradesh giving rise to Indian Standard Time being 5 and half hours or 330 minutes ahead of Greenwich (82 degrees*4 minutes per degree + 0.5 degrees*4 minutes per degree =328 + 2 = 330 minutes). Thus time in every place in India will be the same irrespective of whether it's in the West or East of India. India also doesn't adopt the concept of Day Light Savings Time which is the practise of advancing clock time during the warmer months so that darkness falls at a later clock time. There are however countries like USA, Russia etc who make use of different time zones and also rake in the concept of day light savings time.

However from an Ascendant calculation point of view, it is important to know the Longitude and Latitude of a place as it is determined based on the degree which is rising in the eastern horizon. Taking India as an illustration, every place in India will have a latitude in the North since it is located above the equator in the Northern Hemisphere and likewise every place will have a longitude in the East as it is located towards the right side of the Prime Meridien. For instance, the recorded time maybe the same in both Mumbai & Chennai at any point of time but the Sun rises much earlier in Chennai being in the South of India which is located at about 80° East of the Prime Meridian as compared to a Mumbai which is placed in the West of India at about 72° East of the Prime Meridian. Hence this needs to be factored in the determination of Ascendant. Also when it comes to accuracy and precision, knowing the exact longitude and latitude of the place of birth of an individual  or occurrence of an event also could have a bearing. For instance every nook and corner within a locality may not be of the same latitude and longitude but in many cases we tend to denote an entire city as having the same coordinates. This could lead to some minor discrepancy when determining the exact degree of the Ascendant. For instance an area like Mylapore in Chennai may have coordinated at a slight alteration to the general coordinate which is adopted for Chennai. It would be ideal and more precise if these little matters also be taken care of in order to attain more pin point precision.

The Motions of the Earth and the effect of Sidereal, Solar and Synodic Time Periods

There are 3 kinds of motion associated with the Earth namely which are:
- Rotation
- Revolution
- Precession

It is to be noted that the Earth rotates around it's own axis constantly along with also revolving around the Sun. There is also a third motion which happens very minutely that is known as procession. The Earth wobbles around it's axis which tilts it's relative position to the background stars by approximately 50 seconds a year. This effect of the wobble causes the earth to shift about 1 degree in a span of 72 years (1 degree = 3600 seconds divided by 50 seconds wobble). Applying some mathematics, we can infer that the Earth's axis gets shifted by 180 degrees in 12960 years (72 years for 1 degree multiplied by 180) and to return back to it's original position of 360 degrees takes roughly 25920 years (72 years for 1 degree multiplied by 360). 

This wobbling effect though very minor in nature since it is only barely 50 seconds for a year is not considered within the parlance of Tropical Zodiac and that is the whole reason why sun sign dates differs between the Indian and Western system. The Indian Vedic system adopts the Sidereal Zodiac that takes into account the Wobble effect whereas the Western system takes only the Tropical Zodiac not factoring the Wobbling impact of the Earth. The debate is however endless with respect to the time period in which the wobbling effect started to take place which gives rise to the phenomenon called 'Ayanamsa' which is defined as the angle by which the sidereal ecliptic of a celestial body is less than its tropical ecliptic longitude.

The consensus currently is that Earth has shifted around 24 degrees from its initial position and that is the reason why we see about 24 days difference between the two zodiacs. For instance, the common belief is that the Sun enters the sign of Sagittarius around 22nd of November but the month of Margazhi which is Sun's movement into the sign of Dhanus or Sagittarius occurs only around 16th December as per the almanacs published. The difference will only expand as time keeps travelling but the thing to be noted is that the dates of the Tropical Zodiac will remain more or less constant whereas it's only the dates in the Sidereal Zodiac that will undergo a change of roughly about a day once in every 72 years.

Another important point to keep track is the time taken by the Earth to revolve around the Sun. We know that one year constitutes of 365 days and a leap year is added once every 4 years to make the tally as 366 days. This is because the Earth takes about 365.2422 days to traverse 360 degrees around the Sun. This extra quarter of 0.25 over and above 365 days is added as an extra day once every 4 years (0.25*4 = 1 day) to bridge for this gap. For all practical purposes, a year cannot consist of days in decimals and hence a conventional year is accounted only as 365 days with a leap year of 366 days thrown in once every 4 years. Also it can be noted that Earth revolves about a degree a day around the Sun (365 days for 360 degrees) with the average mean motion of the Earth around the Sun being accounted for about 59 Min 8 seconds in a day.

Lets take a look at some important terminologies with respect to Earth's motion:

Sidereal Day: A Sidereal Day is the time taken by Earth to rotate around it's axis with respect to the stars. This takes about 23 hours 56 minutes and 4.09 seconds.
Sidereal Day = 23 Hours, 56 Minutes, 4.09 Seconds or 0.997270 Days

Solar Day or Tropical Day: A solar day is the time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky. We know a day consists of 24 hours with the time taken by Earth to rotate around it's axis being 23 hours, 56 minutes and 4 seconds. We also know that the Earth revolves around the Sun. To complete a solar day, Earth must rotate an additional portion equal to 1/365 of a full turn. The time required for this extra rotation is 1/365 of a day is approximately close to about 4 minutes. Thus a Solar Day is recorded as 24 hours.
Solar Day = 24 Hours or 1 Day

Synodic Day or Lunar Day: This basically equates to a 'Tithi' within an Indian parlance and denotes the angular distance formed between the Sun and Moon. The Earth revolves around the Sun and the Moon traverses across the Earth's orbit. Since the motions of the Sun and Moon are always varying in speed, the length of a tithi constantly changes and can alternate between 19 hours to 26 hours. However the mean length considered is 24 hours based on the solar time.
Synodic Day = 24 Hours or 1 Day

Sidereal Month: A Sidereal month is the time needed for the Moon to return to the same place against the background of the stars. The Moon revolves around the Earth and takes approximately a little over 27 days to return back to it's orbit. The average daily motion of the moon is said to be about 13 degrees 10 minutes and 35 seconds and to transgress 360 degrees around the Earth is said to take about 27.32 days (360 degrees divided by 13 degrees, 10 minutes and 35 seconds). In Vedic Astrology, the constellations are divided into 27 types of Stars or Nakshatras with each having a time span of 13 degrees 20 minutes. Thus it could be configured that on an average, a Nakshatra span lasts a little over one day considering the daily mean motion of Moon is 13°10'35'' whereas time duration associated with a Nakshatra happens to be 13° 20''.
Sidereal Month = 27 Days, 7 Hours, 43 Minutes, 11.5 Seconds or 27.321661 Days

Solar Month: A solar month is derived based on a Calendar year which consists of 365 days and a leap year added once every 4 years making it 366 days. We know there are 12 months in a year and dividing it by 365 or 366 results in about 30.5 days per month. However for practical purposes we do not normally round the days in a month and the standard days in a month is taken as 30. However some of the months do also have 31 days with February having the least with 28 in normal years and 29 during a leap year.
Solar Month = 30 Days

Synodic or Lunar Month: A Lunar month is considered to be the time period between one full moon to another full moon or one new moon to another new moon. This is based on the relative reference of the Sun and Moon with Earth being the binding factor. Taking the Sun and Moon to be in the exact same position, we already know that a Sidereal month takes approximate 27.32 days. By the time the Moon takes this time to make one path on the Earth's orbit, the Earth would have motioned around 27 degrees towards the Sun. (Since Earth's motion around the Sun is about a degree a day or more precisely 59 min 8 seconds per day). While the Moon is orbiting Earth, the Earth is progressing in its orbit around Sun. After completing a sidereal month, the Moon must move a little further to catch up with the new position having the same angular distance from the Sun. Therefore, a Lunar month takes about 2.2 days longer than a sidereal month making a Lunar Month approx 29 and a half days in length.
Synodic Month = 29 Days 12 Hours 44 Minutes 2.9 Seconds or 29.530589 Days

Sidereal Year: A Sidereal Year is the time that Earth takes to orbit the Sun and return to the same position in relation to the background of the stars. It takes into account the precession caused by the wobbling of the earth and hence it takes about 20 minutes longer than a Tropical year which does not factor into account the effect of precession.
Sidereal Year = 365 Days, 6 Hours, 9 Minutes, 9.5 Seconds or 365.256364 Days

Solar Year or Tropical Year: A Solar Year or Tropical Year which is also known as the Year of the Seasons is the time it takes the Earth to complete a full orbit around the Sun. However while deriving the measure of a Tropical year, the axial tilt of the earth caused due to it's wobbling nature is not considered into account making it slightly shorter in duration than a Sidereal Year.
Solar Year = 365 Days, 5 Hours, 48 Minutes, 46.43 Seconds or 365.242189 Days

Synodic or Lunar Year: A Synodic or Lunar Year is based on the monthly phases of the Moon's cycle which constitutes the relationship based upon the angular distance between Sun and Moon. We have seen that a Lunar month lasts about 29 and a half days and hence to cover 12 cycles will take on an average of about 10-11 days less than a calendar year of 365 days. The number of Lunar months in a Solar Year is said to be about 12.36827.
Synodic Year = 354 Days, 8 Hours, 48 Minutes, 34 Seconds or 354.367060 Days  

Based on the motions of the Earth, the following can also be summarized briefly:
Rotation of the Earth causes the Day and Night Phenomena
The Earth rotates from West to East and one side of the Earth faces the Sun causing day light and the other side gets obscured from the rays of the Sun causing darkness. The Rotation of the Earth also determines the Ascendant in a Horoscope which is the point on the eastern horizon when an individual takes birth. The Ascendant has a direct correlation with the Sun. The Sun rises in the East which dawns a new beginning. In the default Kalapurusha chart, the first sign Aries which also happens to be the exalted sign for Sun is said to denote the Eastern direction. Also the Sages have attributed Sun to be the significator for the first house of birth manifestation.

Revolution of the Earth causes Seasons
As the earth rotates on its axis producing day and night, it also moves about the sun in an elliptical orbit that requires about 365 1/4 days to complete. The earth's axis is tilted with respect to its orbital plane which is what causes the seasons. When the earth's axis points towards the sun, it is summer for that hemisphere. When the earth's axis points away, winter can be expected. Since the tilt of the axis is 23 1/2 degrees, the North Pole never points directly at the Sun, but on the summer solstice it points as close as it can, and on the winter solstice as far as it can. Midway between these two times, in spring and autumn, the spin axis of the earth points 90 degrees away from the sun. This means that during this period, day and night have more or less about the same length of 12 hours.
                           

-> Summer Solstice : Jun 20-22 - Sun reaches it's northern most point when North Pole tilts closest to the Sun - Northern Hemisphere experiences longer days & shorter nights - Southern Hemisphere experiences shorter days & longer nights

-> Winter Solstice : Dec 21-22 - Sun reaches it's southern most point when South Pole tilts closest to the Sun - Northern Hemisphere experiences shorter days & longer nights - Southern Hemisphere experiences longer days & shorter nights

-> Vernal or Spring Equinox : Mar 20-21 - Sun moves northward across the celestial equator with the North Pole starting to tilt towards the Sun indicating climate starting to get hotter in the Northern Hemisphere. Northern Hemisphere experiences Spring with days & nights being equal - Southern Hemisphere experiences Autumn with days & nights being equal.

-> Autumn Equinox : Sep 22-23 - Sun moves southward across the celestial equator with the South Pole starting to tilt towards the Sun indicating climate to start getting hotter in the Southern Hemisphere. Northern Hemisphere experiences Autumn with days & nights being equal - Southern Hemisphere experiences Spring with days & nights being equal.

Note: Autumn always comes after summer season and spring follows winter season. In autumn, the temperature gradually decreases and in spring the temperature starts increasing. The Autumnal Equinox is related to the autumn season and the term vernal equinox is related to the spring season

Additionally, it would also be a subject matter of interest to know about the concepts of Perihelion and Aphelion. Perihelion or Periapsis occurs when Earth moves closest to the Sun which takes place around 1st week of January every year whereas Aphelion or Apoapsis is when Earth moves furthest away from the Sun and this takes place around the first week of July every year.
                               

Precession of the Earth causes Ayanamsa or Precision of Equinoxes
As the Earth wobbles around it's axis, it leads to an axial tilt creating the effect of Ayanamsa which leads to the formation of Sidereal Zodiac based upon the backdrop of the stars as opposed to the Tropical Zodiac which causes seasons and does not factor the wobbling effect into it's equation.