Chronology For the Princess of Mars Trilogy

By Fredrik Ekman
[email protected]

This article attempts to create a complete chronology for the first three books in the Martian series by Edgar Rice Burroughs.
The construction of the chronology has not been without its problems. Burroughs was always a vague and suggestive writer, leaving much to the imagination of his readers. He was sometimes also both inconsistent and even illogical. It has therefore often been necessary to make a choice between two or even more different lengths of time for various activities. It has also sometimes been necessary to guess whether Burroughs refers to Earth time or Barsoom time when he uses terms like "month" and "year." I have assumed that he always means Earth time unless otherwise specified, except for "days" which practically always refers to Barsoom time.

Length of Year and Day

One of the inconsistencies regards the length of the Martian year and day. Burroughs writes in a footnote that "the Martian day is a trifle over 24 hours 37 minutes duration (Earth time)" (GM/16). This piece of information is perhaps taken from Percival Lowell's book Mars. The quoted time is correct (although slightly rounded), but actually refers to the sidereal day, that is the time of the planet's rotation relative to the stars instead of relative to the sun. Due to the combination of the rounding and the different spatial reference the correct time should be over 2.5 minutes longer than stated. This may seem insignificant, but over a period of ten years it will add up to a total difference of several days.
As if this was not enough, Burroughs adds to the confusion later as he writes: "The ten Earth years I had spent upon Barsoom had encompassed but five years and ninety-six days of Martian time, whose days are forty-one minutes longer than ours, and whose years number six hundred and eighty-seven days" (GM/20, my highlighting). Here we find a third length of day quoted. And regardless of which of the three lengths is used, it is impossible to make the equation add up to the ten Earth years. The closest I can come is by supposing that the 687 days are Barsoomian days (whereas in our real world the Martian year is 687 Earth days long) and if we forget that there have been three leap years on Earth during that time. Even then, the day will have to be 48.5 minutes longer on Barsoom than on Earth.
The 687-day long year is again mentioned in WM/1 as the time that John Carter must wait before Dejah Thoris is released from the Temple of the Sun, but on the other hand there is a reference in Burroughs' personal notes saying that a Barsoomian year (ord) is ten months (teean), which in turn is 67 days (padan) (GB/5). This gives a Barsoomian year of 670 days; very close to the real Martian year of 668.6 Martian days.
As can be seen from the above, we have two different lengths of year and no less than four different lengths of day to choose from. We must also decide whether to accept or reject the five years, ninety-six days as being equal to ten years. The choices we make will yield significant differences in the results.
I am inclined to accept that John Carter was on Barsoom for five years, ninety-six days. Since I would give the published sources precedence over personal notes, I am also inclined to go with the 687-day year. The one remaining question then is length of day. Since it is nowhere mentioned that John Carter stayed exactly ten years on Barsoom, we do not have to use my calculated length above. Further, having already discarded the actual Martian year, there is really no reason to use the real-world length of day. Remains to choose between the footnote in chapter 16 and the paragraph in chapter 20 of GM. Somewhat randomly, I choose to use the footnote, mostly because that is what most others tend to refer to. More specifically, I use the sidereal length of day quoted by Lowell, namely 24 hours, 37 minutes, 22.7 seconds (since that was probably Burroughs' original source).
It can perhaps be wondered, in the face of all the abovementioned inconsistencies and errors, whether this kind of activity is worthwhile at all. Regardless of what results we arrive at, they will always be open to interpretation, and so would seem to be of little value. My personal opinion is that this is the very reason why it is important to carry out this study. It gives an opportunity to find and scrutinize the temporal inconsistencies in a more structured manner.

About the Tables

The time of each activity is given both as Barsoom time (BT) and as Earth time (ET). The Barsoom time is given in Barsoomian years and days since John Carter's first arrival on Barsoom, separated by semicolon. When calculating Earth time, I have usually not considered differences between time zones on Barsoom. Earth time is given as a date. For some events there will also be reference to notes with further discussion regarding the event in question.
Unless otherwise specified, all events refer to John Carter. With a few rare exceptions, I have only given one event for each day.
Between the time columns and the event column I have inserted a vertical line. The colour of this line is lighter when the time given is uncertain, usually in relation to the time given immediately above. It follows that darker parts of the line that are preceded by a light part are probably also uncertain by the same amount of time. For example, the departure from Korad is uncertain and may be as many as five days earlier than specified. In consequence, the duel with Zad may also be up to five days earlier, even though it is marked with the dark colour. (If you print this article, make sure to set your browser to print background colours, or this column will turn invisible.)
I cannot guarantee that I have made all calculations correctly, although I have tried to double-check most. Be aware that some seeming inconsistencies between ET and BT may be caused by the fact that I have also considered time of day when calculating. For example, even though arrival at Thark and escape from Thark occur on the same day BT, they are at separate dates ET.
If I ever manage to assemble the energy to do this exercise all over I will probably do it as a neat Excel spreadsheet instead. That will make it possible to toy with different lengths of day and year, and to easily change estimated values.
But now, on with the show!

A Princess of Mars

ET	BT		Event	Note
1866
Mar 5	0;0		Advent upon Mars	1
Mar 6	0;1		The incubator ceremony
Mar 9	0;4		Dejah Thoris is captured
Mar 15	0;10		Defends Dejah Thoris in the audience chamber
Mar 19	0;14		Departure from Korad	2
Mar 20	0;15		Duel with Zad
Apr 7	0;34		Kantos Kan arrives at Helium
Apr 7	0;34		Arrival at Thark	3
Apr 8	0;34		Escape from Thark
Apr 10	0;37		Captured by Warhoon
Apr 13	0;40		Warhoons march for home
Apr 16	0;43		Arrival at Warhoon	4
Apr 24	0;50		Murders jailer
Apr 25	0;52		Kantos Kan arrives at Warhoon
Apr 28	0;54		Kantos Kan imprisoned
May 1	0;57		Escape during the great games
May 4	0;60		Sets out from Warhoon
May 18	0;74		Arrival at atmosphere factory
May 19	0;75		Guest at the Ptor brothers'
May 23	0;79		Sets out for Zodanga	5
May 30	0;86		Kantos Kan arrives at Zodanga
Jun 2	0;89		Arrival at Zodanga
Jun 7	0;93		Finds Dejah Thoris
Jun 8	0;94		Battle outside Thark
Jun 11	0;97		Tharks march toward Zodanga
Jun 22	0;107		Battle of Zodanga
Jun 23	0;109		Tharks arrive outside Helium
Jun 24	0;110		The battle of Helium is won
Jul 6	0;121		Tharks march from Helium	6
Jul 27	0;142		Married with Dejah Thoris	7
1871
Feb 9	2;383		Dejah Thoris lays an egg	8
Mar 4	2;404		Thuvia of Ptarth enslaved by the therns	9
1876
Jan 31	5;92		Message about atmosphere factory received
Feb 4	5;96		Saves the day and returns to Earth	10

1. The date 5th of March ET is easily arrived at by a careful reading of the first two chapters of PM. It is clear that John Carter left his earthly life behind some time around midnight on the night preceding the 5th of March. Burroughs later seems to have been confused about this (see note 13).
2. Burroughs gives several references for the extent of the stay in Korad, all conflicting to some extent. The time here presented is in accordance with my article "The Duration of John Carter's Stay in Korad: A Contradiction".
3. The figure 34 is contradicted in the novel by the statement that Thark was entered "thirty days after my advent upon Barsoom" (PM/16). That statement, however, is based on an erroneously calculated stay in Korad (see note 2). In addition, the figure 34 makes sense in the light of a later statement that Kantos Kan reached Helium "about the time of our coming to Thark" (PM/19).
4. The chain of events following the arrival at Warhoon is in a way the most problematic passage in the entire novel. John Carter cannot even say whether he lay imprisoned for "days, or weeks, or months" (PM/18). Two clues prompted me to assume the relatively short passage of time (seven days until the murder of his jailer) recorded here. One is the time of Kantos Kan's arrival. He came to Warhoon after having spent an unknown amount of time with the navy of Helium searching among the northern tribes and in the process wiping out two entire communities of green men. The fourteen days assumed here would, I think, be a minimal time for that activity. At any rate, it should not have been more than 25 or 30 days. The other clue is the fact that the Warhoons after a delay of only three days on march feared that they would not be able to return in time for the great games. If we assume that the Warhoons were marching for Thark, then we know that they were no more than three days' march from their goal (since that is how far John Carter had marched with Dejah Thoris and Sola), so the expedition was only supposed to take nine more days (three days to Thark, six days back) plus time accounted for delays and battle. It is probable that the games were scheduled to start within or shortly after ten days after the march back to Warhoon was commenced, that is about 50 days after John Carter's arrival on Barsoom. Since we do not know at what day of the games John Carter fought, however, we can allow for some slack and the present assumptions are consequently not unlikely.
5. Regarding John Carter's stay with the Ptor family, we are only told that he remained for "several days" (PM/20). My guess here at four days is probably a minimal interpretation of "several," but I feel that John Carter probably wanted to be on his way as quickly as possible.
6. It is stated that the Tharks were feasted for ten days (PM/27), although it is not clear whether the first night after the battle is included in this figure or not. I have here assumed that it is not.
7. A total of 142 days after arrival assumes that the errors of the previous uncertain times balance one another. At worst, it could be 13 days less or about as much more, depending on the correctness of my guesswork. It is also interesting to note that although John Carter often states that he was in the service of Helium for nine years, his adventures up to this point actually took less than five months, leaving closer to ten years until his alotted time is up. This could be interpreted in several different ways. Either, he mentioned nine years as an extremely approximate figure, or he did not enter the service of Helium immediately after his marriage (which seems unlikely). A third alternative is that I gravely underestimated the time during which he was a prisoner of Warhoon (see note 4).
8. Carthoris' egg had been laid nearly five years before the atmosphere factory incident (PM/27). This cannot possibly be five years BT, or the egg would have been laid while Dejah Thoris was still a prisoner of Zodanga. Thus, it must be 5 years ET, or approximately 2 years 405 days BT. This is too close to 2 years 400 days not to be used as a nice and round figure, although we cannot of course know the exact time.
9. At the coming of John Carter to Dor, Thuvia had been a slave for fifteen years (GM/4). Assuming Earth years, she should have arrived at the goal of her pilgrimage about this time.
10. John Carter saves Barsoom and passes out late in the evening on Barsoom, or just after midnight on Earth according to my calculations. By coincidence(?) this rhymes very well with the novel, since it is night when he awakens on Earth. He was thus probably not unconscious for very long.

The Gods of Mars

ET	BT		Event	Note
1884
Apr 4	9;255		Carthoris sees the face of Issus	11
1886
Feb 9	10;227		Tardos Mors & Mors Kajak set out for Carthoris	12
Feb 23	10;241		The expedition is captured by the yellow men
Mar 4	10;249		Second advent upon Mars	13
Mar 4	10;249		Dejah Thoris leaves Helium
Mar 5	10;250		The black men attack
Mar 5	10;251		Captured by the black men
Mar 5	10;251		Imprisoned on Shador
Mar 6	10;252		Rebellion in the arena
Mar 7	10;252		Flight from Omean
Mar 8	10;253		Liberation of Tars Tarkas
Mar 8	10;254		Dejah Thoris captured by the black men
Mar 9	10;255		Rescued by the Xavarian	14
Mar 10	10;256		Judgement at the Temple of Reward
Mar 11	10;256		Kidnapped by Zat Arrras
1887
Feb 12	10;591		Message relayed to Carthoris	15
Mar 13	10;614		Fleet is ready to sail from Hastor
Mar 20	10;621		Rescued from the pits
Mar 22	10;623		The air battle	16
Mar 23	10;624		The fight in the temple

11. Carthoris saw the face of Issus nearly one year before he first met his father (GM/10). In this case, it has to be a Barsoomian year. We do not know the exact date, of course.
12. Mors Kajak and Tardos Mors set out to rescue Carthoris one month before John Carter was rescued by the Xavarian and contact was lost with them two weeks before the rescue (GM/16). Earth weeks and months are here assumed. We do not know whether the times are exact or approximate, but in wont of better I have assumed exact.
13. Burroughs is very careful to point out in his foreword to PM that John Carter dies (and consequently goes to Barsoom) on the night before the 4th of March. He apparently meant this to be exactly (probably to the hour) 20 years after the first passage. Unfortunately, the first passage was actually on the 5th of March (see note 1). Accepting this slight inconsistency we find that John Carter should arrive on Mars after the fifth zode. This is one or two zodes later than would be assumed based on the initial sequence of events, but that need not bother us greatly. After all, we do not know exactly in what time zone he arrived. And speaking of time zones, it is interesting how, this close to the pole, day and night seem to go on just like anywhere on the planet. We must assume that John Carter happened to arrive at a conveniently long period of solstice, which also happens to be the case whenever in the future he visits the areas near the poles.
14. After having picked up John Carter, the Xavarian made the journey back to Helium in only a couple of hours, which does not seem very likely (compare note 16). Of course, we shall have to accept what Burroughs writes.
15. John Carter had calculated 300 days of confinement up to this point. After his escape, however, he realised that he had counted 35 days too few. I have chosen to account all 35 days to this first part of his imprisonment. Note that the uncertainty of this date does not affect the dates following in the rest of the book.
16. Again the journey is extremely swift. I estimate that a swift flier would take a full day to complete the trip from Hastor to the south pole. Here a fleet of slower battleships do it in about half that time. The events after the battle are also questionable. The heliumetic fleet does not enter Omean until after dark, yet the troops apparently reach the temple before dawn. Within that time they descend the shaft (which should be rather slow work with a fleet of five hundred), defeat the remaining forces, take over the submarine, plug up the shaft and travel the subterranean passages to the temple. All this should leave at most two zodes for transporting the troops (five thousand strong) with the submarine. If we assume a capacity of 125 men, then each return trip (including embarking and disembarking) would have to take less than seven and a half minute.

The Warlord of Mars

ET	BT		Event	Note
1888
Mar 9	11;280		Shadowing Thurid	17
Mar 10	11;281		Encounter with Lakor	18
Mar 11	11;282		Visual contact with Dejah Thoris
Mar 14	11;285		At Matai Shang's tower
Mar 16	11;287		Shot down by Thurid
Mar 17	11;288		Meeting with Torkar Bar
Mar 18	11;289		Battle of Kaol
Mar 19	11;290		Meeting with Thuvan Dihn
Mar 20	11;291		Kulan Tith has a change of heart
Mar 22	11;293		Recommenced pursuit
Mar 24	11;294		Crash against ice barrier
Mar 28	11;299		Finds the Carrion Caves
Mar 29	11;300		Helps Talu	19
Apr 2	11;303		Arrival outside Kadabra
Apr 3	11;304		Enters Kadabra
Apr 4	11;305		Accepted as royal guards
Apr 5	11;307		Thrown into the pit of plenty
Apr 15	11;316		Battle of Kadabra
Apr 25	11;326		Talu officially becomes jeddak	20
May 27	11;358		Departure from Ptarth	21
Jun 1	11;363		Arrival at Helium	22

17. We are told that half the year from Dejah Thoris' imprisonment had passed, "or would on the morrow" (WM/1). The problem with this is that half a year is 343.5 days, so if half a year were to have passed on the morrow, then it had already done so in the evening. It is probable that John Carter is referring to a date in some Martian calendar, the structure of which we know nothing about. I have assumed that 343.5 days have passed when the book begins.
18. The initial chain of events in the book is problematic, mostly because it is set in underground passages, so no indication of night or day is given. I feel, however, that the approximations here given are reasonable and that the margin for error stays within one day.
19. This time is uncertain, because we do not know how long the passage through the 27 chambers of the carrion caves took. Since it was day when the caves were found, and day again when Talu and his would-be assassins were spied, it is reasonable to assume that the passage took one night.
20. There is no indication as to the length of time spent in Kadabra waiting for this event. The ten days here quoted is a pure guess.
21. The duration of the stay in Ptarth is cited as one month and I have as always assumed ET, plus two days for the flight from Kadabra.
22. Before returning to Helium, the company stayed for an unknown period in Kaol. This period, however, must have been very brief, for when John Carter sees Thuvan Dihn in the Temple of Reward, he remembers having seen him in Ptarth only "a few days since" (WM/16).

Chronology For the Princess of Mars Trilogy

By Fredrik Ekman
[email protected]

This article attempts to create a complete chronology for the first three books in the Martian series by Edgar Rice Burroughs.
The construction of the chronology has not been without its problems. Burroughs was always a vague and suggestive writer, leaving much to the imagination of his readers. He was sometimes also both inconsistent and even illogical. It has therefore often been necessary to make a choice between two or even more different lengths of time for various activities. It has also sometimes been necessary to guess whether Burroughs refers to Earth time or Barsoom time when he uses terms like "month" and "year." I have assumed that he always means Earth time unless otherwise specified, except for "days" which practically always refers to Barsoom time.

Length of Year and Day

One of the inconsistencies regards the length of the Martian year and day. Burroughs writes in a footnote that "the Martian day is a trifle over 24 hours 37 minutes duration (Earth time)" (GM/16). This piece of information is perhaps taken from Percival Lowell's book Mars. The quoted time is correct (although slightly rounded), but actually refers to the sidereal day, that is the time of the planet's rotation relative to the stars instead of relative to the sun. Due to the combination of the rounding and the different spatial reference the correct time should be over 2.5 minutes longer than stated. This may seem insignificant, but over a period of ten years it will add up to a total difference of several days.
As if this was not enough, Burroughs adds to the confusion later as he writes: "The ten Earth years I had spent upon Barsoom had encompassed but five years and ninety-six days of Martian time, whose days are forty-one minutes longer than ours, and whose years number six hundred and eighty-seven days" (GM/20, my highlighting). Here we find a third length of day quoted. And regardless of which of the three lengths is used, it is impossible to make the equation add up to the ten Earth years. The closest I can come is by supposing that the 687 days are Barsoomian days (whereas in our real world the Martian year is 687 Earth days long) and if we forget that there have been three leap years on Earth during that time. Even then, the day will have to be 48.5 minutes longer on Barsoom than on Earth.
The 687-day long year is again mentioned in WM/1 as the time that John Carter must wait before Dejah Thoris is released from the Temple of the Sun, but on the other hand there is a reference in Burroughs' personal notes saying that a Barsoomian year (ord) is ten months (teean), which in turn is 67 days (padan) (GB/5). This gives a Barsoomian year of 670 days; very close to the real Martian year of 668.6 Martian days.
As can be seen from the above, we have two different lengths of year and no less than four different lengths of day to choose from. We must also decide whether to accept or reject the five years, ninety-six days as being equal to ten years. The choices we make will yield significant differences in the results.
I am inclined to accept that John Carter was on Barsoom for five years, ninety-six days. Since I would give the published sources precedence over personal notes, I am also inclined to go with the 687-day year. The one remaining question then is length of day. Since it is nowhere mentioned that John Carter stayed exactly ten years on Barsoom, we do not have to use my calculated length above. Further, having already discarded the actual Martian year, there is really no reason to use the real-world length of day. Remains to choose between the footnote in chapter 16 and the paragraph in chapter 20 of GM. Somewhat randomly, I choose to use the footnote, mostly because that is what most others tend to refer to. More specifically, I use the sidereal length of day quoted by Lowell, namely 24 hours, 37 minutes, 22.7 seconds (since that was probably Burroughs' original source).
It can perhaps be wondered, in the face of all the abovementioned inconsistencies and errors, whether this kind of activity is worthwhile at all. Regardless of what results we arrive at, they will always be open to interpretation, and so would seem to be of little value. My personal opinion is that this is the very reason why it is important to carry out this study. It gives an opportunity to find and scrutinize the temporal inconsistencies in a more structured manner.

About the Tables

The time of each activity is given both as Barsoom time (BT) and as Earth time (ET). The Barsoom time is given in Barsoomian years and days since John Carter's first arrival on Barsoom, separated by semicolon. When calculating Earth time, I have usually not considered differences between time zones on Barsoom. Earth time is given as a date. For some events there will also be reference to notes with further discussion regarding the event in question.
Unless otherwise specified, all events refer to John Carter. With a few rare exceptions, I have only given one event for each day.
Between the time columns and the event column I have inserted a vertical line. The colour of this line is lighter when the time given is uncertain, usually in relation to the time given immediately above. It follows that darker parts of the line that are preceded by a light part are probably also uncertain by the same amount of time. For example, the departure from Korad is uncertain and may be as many as five days earlier than specified. In consequence, the duel with Zad may also be up to five days earlier, even though it is marked with the dark colour. (If you print this article, make sure to set your browser to print background colours, or this column will turn invisible.)
I cannot guarantee that I have made all calculations correctly, although I have tried to double-check most. Be aware that some seeming inconsistencies between ET and BT may be caused by the fact that I have also considered time of day when calculating. For example, even though arrival at Thark and escape from Thark occur on the same day BT, they are at separate dates ET.
If I ever manage to assemble the energy to do this exercise all over I will probably do it as a neat Excel spreadsheet instead. That will make it possible to toy with different lengths of day and year, and to easily change estimated values.
But now, on with the show!

A Princess of Mars

ET	BT		Event	Note
1866
Mar 5	0;0		Advent upon Mars	1
Mar 6	0;1		The incubator ceremony
Mar 9	0;4		Dejah Thoris is captured
Mar 15	0;10		Defends Dejah Thoris in the audience chamber
Mar 19	0;14		Departure from Korad	2
Mar 20	0;15		Duel with Zad
Apr 7	0;34		Kantos Kan arrives at Helium
Apr 7	0;34		Arrival at Thark	3
Apr 8	0;34		Escape from Thark
Apr 10	0;37		Captured by Warhoon
Apr 13	0;40		Warhoons march for home
Apr 16	0;43		Arrival at Warhoon	4
Apr 24	0;50		Murders jailer
Apr 25	0;52		Kantos Kan arrives at Warhoon
Apr 28	0;54		Kantos Kan imprisoned
May 1	0;57		Escape during the great games
May 4	0;60		Sets out from Warhoon
May 18	0;74		Arrival at atmosphere factory
May 19	0;75		Guest at the Ptor brothers'
May 23	0;79		Sets out for Zodanga	5
May 30	0;86		Kantos Kan arrives at Zodanga
Jun 2	0;89		Arrival at Zodanga
Jun 7	0;93		Finds Dejah Thoris
Jun 8	0;94		Battle outside Thark
Jun 11	0;97		Tharks march toward Zodanga
Jun 22	0;107		Battle of Zodanga
Jun 23	0;109		Tharks arrive outside Helium
Jun 24	0;110		The battle of Helium is won
Jul 6	0;121		Tharks march from Helium	6
Jul 27	0;142		Married with Dejah Thoris	7
1871
Feb 9	2;383		Dejah Thoris lays an egg	8
Mar 4	2;404		Thuvia of Ptarth enslaved by the therns	9
1876
Jan 31	5;92		Message about atmosphere factory received
Feb 4	5;96		Saves the day and returns to Earth	10

1. The date 5th of March ET is easily arrived at by a careful reading of the first two chapters of PM. It is clear that John Carter left his earthly life behind some time around midnight on the night preceding the 5th of March. Burroughs later seems to have been confused about this (see note 13).
2. Burroughs gives several references for the extent of the stay in Korad, all conflicting to some extent. The time here presented is in accordance with my article "The Duration of John Carter's Stay in Korad: A Contradiction".
3. The figure 34 is contradicted in the novel by the statement that Thark was entered "thirty days after my advent upon Barsoom" (PM/16). That statement, however, is based on an erroneously calculated stay in Korad (see note 2). In addition, the figure 34 makes sense in the light of a later statement that Kantos Kan reached Helium "about the time of our coming to Thark" (PM/19).
4. The chain of events following the arrival at Warhoon is in a way the most problematic passage in the entire novel. John Carter cannot even say whether he lay imprisoned for "days, or weeks, or months" (PM/18). Two clues prompted me to assume the relatively short passage of time (seven days until the murder of his jailer) recorded here. One is the time of Kantos Kan's arrival. He came to Warhoon after having spent an unknown amount of time with the navy of Helium searching among the northern tribes and in the process wiping out two entire communities of green men. The fourteen days assumed here would, I think, be a minimal time for that activity. At any rate, it should not have been more than 25 or 30 days. The other clue is the fact that the Warhoons after a delay of only three days on march feared that they would not be able to return in time for the great games. If we assume that the Warhoons were marching for Thark, then we know that they were no more than three days' march from their goal (since that is how far John Carter had marched with Dejah Thoris and Sola), so the expedition was only supposed to take nine more days (three days to Thark, six days back) plus time accounted for delays and battle. It is probable that the games were scheduled to start within or shortly after ten days after the march back to Warhoon was commenced, that is about 50 days after John Carter's arrival on Barsoom. Since we do not know at what day of the games John Carter fought, however, we can allow for some slack and the present assumptions are consequently not unlikely.
5. Regarding John Carter's stay with the Ptor family, we are only told that he remained for "several days" (PM/20). My guess here at four days is probably a minimal interpretation of "several," but I feel that John Carter probably wanted to be on his way as quickly as possible.
6. It is stated that the Tharks were feasted for ten days (PM/27), although it is not clear whether the first night after the battle is included in this figure or not. I have here assumed that it is not.
7. A total of 142 days after arrival assumes that the errors of the previous uncertain times balance one another. At worst, it could be 13 days less or about as much more, depending on the correctness of my guesswork. It is also interesting to note that although John Carter often states that he was in the service of Helium for nine years, his adventures up to this point actually took less than five months, leaving closer to ten years until his alotted time is up. This could be interpreted in several different ways. Either, he mentioned nine years as an extremely approximate figure, or he did not enter the service of Helium immediately after his marriage (which seems unlikely). A third alternative is that I gravely underestimated the time during which he was a prisoner of Warhoon (see note 4).
8. Carthoris' egg had been laid nearly five years before the atmosphere factory incident (PM/27). This cannot possibly be five years BT, or the egg would have been laid while Dejah Thoris was still a prisoner of Zodanga. Thus, it must be 5 years ET, or approximately 2 years 405 days BT. This is too close to 2 years 400 days not to be used as a nice and round figure, although we cannot of course know the exact time.
9. At the coming of John Carter to Dor, Thuvia had been a slave for fifteen years (GM/4). Assuming Earth years, she should have arrived at the goal of her pilgrimage about this time.
10. John Carter saves Barsoom and passes out late in the evening on Barsoom, or just after midnight on Earth according to my calculations. By coincidence(?) this rhymes very well with the novel, since it is night when he awakens on Earth. He was thus probably not unconscious for very long.

The Gods of Mars

ET	BT		Event	Note
1884
Apr 4	9;255		Carthoris sees the face of Issus	11
1886
Feb 9	10;227		Tardos Mors & Mors Kajak set out for Carthoris	12
Feb 23	10;241		The expedition is captured by the yellow men
Mar 4	10;249		Second advent upon Mars	13
Mar 4	10;249		Dejah Thoris leaves Helium
Mar 5	10;250		The black men attack
Mar 5	10;251		Captured by the black men
Mar 5	10;251		Imprisoned on Shador
Mar 6	10;252		Rebellion in the arena
Mar 7	10;252		Flight from Omean
Mar 8	10;253		Liberation of Tars Tarkas
Mar 8	10;254		Dejah Thoris captured by the black men
Mar 9	10;255		Rescued by the Xavarian	14
Mar 10	10;256		Judgement at the Temple of Reward
Mar 11	10;256		Kidnapped by Zat Arrras
1887
Feb 12	10;591		Message relayed to Carthoris	15
Mar 13	10;614		Fleet is ready to sail from Hastor
Mar 20	10;621		Rescued from the pits
Mar 22	10;623		The air battle	16
Mar 23	10;624		The fight in the temple

11. Carthoris saw the face of Issus nearly one year before he first met his father (GM/10). In this case, it has to be a Barsoomian year. We do not know the exact date, of course.
12. Mors Kajak and Tardos Mors set out to rescue Carthoris one month before John Carter was rescued by the Xavarian and contact was lost with them two weeks before the rescue (GM/16). Earth weeks and months are here assumed. We do not know whether the times are exact or approximate, but in wont of better I have assumed exact.
13. Burroughs is very careful to point out in his foreword to PM that John Carter dies (and consequently goes to Barsoom) on the night before the 4th of March. He apparently meant this to be exactly (probably to the hour) 20 years after the first passage. Unfortunately, the first passage was actually on the 5th of March (see note 1). Accepting this slight inconsistency we find that John Carter should arrive on Mars after the fifth zode. This is one or two zodes later than would be assumed based on the initial sequence of events, but that need not bother us greatly. After all, we do not know exactly in what time zone he arrived. And speaking of time zones, it is interesting how, this close to the pole, day and night seem to go on just like anywhere on the planet. We must assume that John Carter happened to arrive at a conveniently long period of solstice, which also happens to be the case whenever in the future he visits the areas near the poles.
14. After having picked up John Carter, the Xavarian made the journey back to Helium in only a couple of hours, which does not seem very likely (compare note 16). Of course, we shall have to accept what Burroughs writes.
15. John Carter had calculated 300 days of confinement up to this point. After his escape, however, he realised that he had counted 35 days too few. I have chosen to account all 35 days to this first part of his imprisonment. Note that the uncertainty of this date does not affect the dates following in the rest of the book.
16. Again the journey is extremely swift. I estimate that a swift flier would take a full day to complete the trip from Hastor to the south pole. Here a fleet of slower battleships do it in about half that time. The events after the battle are also questionable. The heliumetic fleet does not enter Omean until after dark, yet the troops apparently reach the temple before dawn. Within that time they descend the shaft (which should be rather slow work with a fleet of five hundred), defeat the remaining forces, take over the submarine, plug up the shaft and travel the subterranean passages to the temple. All this should leave at most two zodes for transporting the troops (five thousand strong) with the submarine. If we assume a capacity of 125 men, then each return trip (including embarking and disembarking) would have to take less than seven and a half minute.

The Warlord of Mars

ET	BT		Event	Note
1888
Mar 9	11;280		Shadowing Thurid	17
Mar 10	11;281		Encounter with Lakor	18
Mar 11	11;282		Visual contact with Dejah Thoris
Mar 14	11;285		At Matai Shang's tower
Mar 16	11;287		Shot down by Thurid
Mar 17	11;288		Meeting with Torkar Bar
Mar 18	11;289		Battle of Kaol
Mar 19	11;290		Meeting with Thuvan Dihn
Mar 20	11;291		Kulan Tith has a change of heart
Mar 22	11;293		Recommenced pursuit
Mar 24	11;294		Crash against ice barrier
Mar 28	11;299		Finds the Carrion Caves
Mar 29	11;300		Helps Talu	19
Apr 2	11;303		Arrival outside Kadabra
Apr 3	11;304		Enters Kadabra
Apr 4	11;305		Accepted as royal guards
Apr 5	11;307		Thrown into the pit of plenty
Apr 15	11;316		Battle of Kadabra
Apr 25	11;326		Talu officially becomes jeddak	20
May 27	11;358		Departure from Ptarth	21
Jun 1	11;363		Arrival at Helium	22

17. We are told that half the year from Dejah Thoris' imprisonment had passed, "or would on the morrow" (WM/1). The problem with this is that half a year is 343.5 days, so if half a year were to have passed on the morrow, then it had already done so in the evening. It is probable that John Carter is referring to a date in some Martian calendar, the structure of which we know nothing about. I have assumed that 343.5 days have passed when the book begins.
18. The initial chain of events in the book is problematic, mostly because it is set in underground passages, so no indication of night or day is given. I feel, however, that the approximations here given are reasonable and that the margin for error stays within one day.
19. This time is uncertain, because we do not know how long the passage through the 27 chambers of the carrion caves took. Since it was day when the caves were found, and day again when Talu and his would-be assassins were spied, it is reasonable to assume that the passage took one night.
20. There is no indication as to the length of time spent in Kadabra waiting for this event. The ten days here quoted is a pure guess.
21. The duration of the stay in Ptarth is cited as one month and I have as always assumed ET, plus two days for the flight from Kadabra.
22. Before returning to Helium, the company stayed for an unknown period in Kaol. This period, however, must have been very brief, for when John Carter sees Thuvan Dihn in the Temple of Reward, he remembers having seen him in Ptarth only "a few days since" (WM/16).