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Timelines of the Battlestar Galactica series
The timeline is given in "Earth" years, BC and AD, not by Colonial yahren.
- Before c. 5397 BC
- The Beings of Light intervene at the beginning of human development on the planet that would come to be known as Kobol. Adama refers to these beings as the "Mother Race".
- c. 5397 BC
- The beginning of the Colonial calendar.
- c. 4050 BC
- c. 4050 BC to c. 40 AD
Exodus through 20th Century
- 69 BC - 30 BC
- c. 950 AD
- The Cylons attack the Hasari, whose territory neighbors the Colonies, who intervene to assist their neighbor. As a result of this intervention, the Thousand Yahren War begins between the Colonies and the Cylon Empire. 
- c. 1450 AD
- Approximate time that Galactica is launched. Back then, the celestial chambers on Galactica were used to confirm navigational headings. 
- 1776 AD
- Xavier arrives in Revolutionary America and tries to change history. Troy, Dillon and Jamie Hamilton follow him, and thwart his plans, but he apparently escapes to another time frame. 
- prior to 1850
- 1910: Battle of Caprica.
- 1917: Starbuck is born on Caprica. His father is Chameleon.
- 1924: The Attack on Umbra describes a sneak attack by the Cylons. Nearly three thousand children were orphaned, including Starbuck
- September 1: Earth's World War II begins.
- 1943: Boxey is born to Serina on Caprica.
- 1944: Xavier arrives in Nazi Germany and poses as a British scientist and Nazi sympathizer. He volunteers to work with the V-2 rocket program and introduces Colonial technology, in hopes of changing history by ensuring a Nazi victory in World War Two.
- 1947: The United States Air Force begins Project Blue Book, a 22 year long investigation into unidentified flying objects.
- 1948: The Fifth Fleet engages the Cylons at the Battle of Molecay. Pegasus is the only Colonial vessel to survive. Commander Cain, realizing that the Cylons were doubtless lying in wait along the entire route back to the Colonies, orders Pegasus out into deep space towards the Krillian Star System and Gamoray.
The episodes and events of the Original Series are set during this period.
1951 - 1979
The Cylons, over this 30 year period, develop completely new technologies and evolve considerably - "beyond the wildest fears" of the Colonials, according to Dr. Zee. These new technologies include improved Cylon Raiders and the creation of humanoid Cylons.
Also, during this period, the Imperious Leader is apparently replaced, as his voice is considerably different by 1980.
- 1960: The last attack by the Cylons on the Colonial fleet until 1980. 
- 1970: Starbuck is stranded on a desolate planetoid, where he rebuilds the Centurion named Cyrus (nicknamed "Cy" by Starbuck). Some time later at this same location, Dr. Zee is born to the mysterious woman, Angela. 
- After 1970:
- Dr. Zee's ship catches up to the Fleet. .
- Lt. Boomer is promoted to Colonel.
- Commander Adama grows a beard.
- Boxey begins to go by the name "Troy" as he grows older.
Galactica's long range probes arrive in the Solar System. They positively identify the third planet as Earth. Galactica and the Colonial Fleet reach Earth. 
- Troy, Dillon and Jamie head back in time to World War II and then to the American Revolution to find Xavier.  The team is apparently successful in stopping Xavier, as there are no apparent changes to Earth's history. Xavier escapes being brought into custody, however, and remains in Earth's past. While there, he perfects a process of cellular transformation which can allow him to assume the appearance of others. 
- Jamie returns to Earth, and back to the job she was offered with the United Broadcasting Corporation. 
- In light of the unknown aircraft violating U.S. airspace, which are in reality Colonial Vipers, the United States Air Force dedicates new funds to the tracking of U.F.O.s.
- Dr. Zee leads a project to build a new saucer-shaped fighter craft, designed to thwart the Cylons.
- The Cylons determine to test some of their new technologies on the Colonial refugees. They plan to first attack the freighter Delphi, a straggling vessel in the Colonial Fleet, which happens to function as the Fleet' school.
- Troy and Dillon spend a few days away from the children on an unknown mission.
- Having spent an inordinate amount of money investigating the Super Scouts, Colonel Sydell's budget is questioned by his superiors in the United States Air Force.
- Xavier returns to the present time from Earth's past, and assumes the form of Lt. Nash of Galactica. 
Galactica 1980 episode "Spaceball."
- Xavier remains at large on Earth, without a Viper, stranded in the present and on the ground.
- In another test of their new technologies, the Cylons send out new, advanced fighters, manned by Centurions and humanoid Cylons, to search for the elusive Colonial fleet.
- October 31 - November 1, 1980
- Late 1980
- Galactica 1980 episode "Space Croppers".
- Galactica maintains its first colony on Earth, and the Super Scouts remain there, relocating from the baseball camp where they had been staying.
- Galactica 1980 episode "The Return of Starbuck".
- The scripted but only partially shot episode "The Day They Kidnapped Cleopatra" would have taken place here.
- The planned but never filmed Starbuck episode "The Wheel of Fire" would have taken place at this time.
In Dr. Zee's projection of what could have happened in the future, environmental damage and population expansion has rendered Paradise Valley polluted and crowded. If Dr. Zee's warning was in fact heeded by the people of Paradise Valley, however, these events may not have come to pass.
The central year of this timeline is 1980, the year when the series is set. In promotional material and subsequent interviews, it has been noted that Galactica 1980 was set 30 years after the events of the Original Series. This was done in large part to explain the cast changes, and is chiefly supported on screen by the aging of Troy, who was a child in the first series.
- At the beginning of "Saga of a Star World", it is mentioned that the peace conference is being held at the beginning of the 7th millennium of human history, which would mean human history was just crossing into its 6,000th year. 6,000 years prior to "Saga of a Star World", which is noted later in this timeline as happening in 1950, would be circa 4,000 BC.
- A partially filmed, but never aired episode of Galactica 1980, entitled "The Day They Kidnapped Cleopatra" was partially set in 30 BCE. The announcement of the cancellation of the series by ABC came during the filming, and the episode was never completed. This episode would have brought back the time travel plot device used in the first episode. Additionally, Egyptian themes were used frequently in Battlestar Galactica, such as the city of Eden in "Lost Planet of the Gods".
- The Thousand Yahren War begins 1,000 years before "Saga of a Star World" which, as noted later in this timeline, is set around 1950.
- A 500 year old celestial chamber is depicted in "The Hand of God".
- The trip to 1776 is referred to at the end of "Galactica Discovers Earth, Part III" but not shown on screen. Xavier's plans are mentioned at the start of "Spaceball".
- Adama reveals he is over a hundred yahrens old in "Lost Planet of the Gods".
- Based on the age of Dirk Benedict during the filming of the Original Series. Starbuck is revealed to be from Caprica, as well as Chameleon being his father in "The Man with Nine Lives".
- Jamie Hamilton makes a slight error when she tells the Galacticans that "20 years later, in 1939, World War II broke out" in "Galactica Discovers Earth, Part I". However, she was reciting this from memory, so it's an understandable error.
- As confirmed by Jamie Hamilton in her conversation to the Galacticans in Zee's chamber (Galactica Discovers Earth, Part II).
- This calculation is based on Noah Hathaway's age during the filming of the Original Series. This would make Boxey seven years old in "Saga of a Star World" and 37 years of age in "Galactica Discovers Earth, Part I" -- which happened to be the age of Kent McCord when he played the role.
- Described in "Galactica Discovers Earth, Part II".
- Depicted in "Galactica Discovers Earth, Part II" and "Galactica Discovers Earth, Part III".
- Project Blue Book is mentioned in a disclaimer at the end of every Galactica 1980 episode. Colonel Sydell's new organization within the US Air Force in the series has a similar mandate, and the disclaimer was apparently put in place to assure viewers that Sydell's organization was fictitious, and not to be confused with the real project that had concluded years before.
- Two yahrens prior to the events of "The Living Legend, Part I".
- Officially, Galactica 1980 was set 30 years after the events of the Original Series. This piece of information is never specifically mentioned on screen, but was mentioned in promotional advertising and noted in background material for the program.
- The increased technological prowess of the Cylons is described in "The Super Scouts, Part I" and "The Night the Cylons Landed, Part I".
- When the Imperious Leader is shown in "Space Croppers", he is no longer voiced by Patrick Macnee, but instead by Dennis Haysbert.
- Troy refers to Apollo's death in "Galactica Discovers Earth, Part I". This apparently happens before the events depicted in "The Return of Starbuck" as Starbuck does not mention Apollo when relating to Boomer people he wishes to say goodbye to. In addition, Apollo's death is apparently a mystery to the Fleet, or so the script for the unfilmed episode "The Wheel of Fire" indicates.
- Based on the age of Barry Van Dyke at the time of filming.
- Based on the age of actress Robyn Douglass at the time of filming, who portrayed Jamie Hamilton. She identifies herself as an American in "Galactica Discovers Earth, Part III".
- There has not been a Cylon attack in almost a generation prior to "The Super Scouts, Part I". A generation is typically denoted as 20 years.
- Events of the flashback sequence of "The Return of Starbuck". Dr. Zee is a pre-teen child, who appears to be roughly ten years of age. Reasoning backward, he was born c. 1970.
- The voyage of Dr. Zee's ship is shown in "The Return of Starbuck"
- By the time of "Galactica Discovers Earth, Part I" Boomer has assumed this rank, while he still held this rank in the flashback scenes in "The Return of Starbuck".
- Adama has a large Moses like beard throughout 1980, but did not have it in the flashback scenes in "The Return of Starbuck".
- Troy mentions this in "Galactica Discovers Earth, Part I", although Adama still refers to him as Boxey in a private conversation before being shown the invisibility field.
- According to Dorothy Carlyle, Dr. Mortinson had been working on nuclear degeneration for three years as of "Galactica Discovers Earth, Part I".
- "Galactica Discovers Earth, Part I".
- Troy, Dillon and Jamie are about to head off on this mission at the end of "Galactica Discovers Earth, Part III"
- No reference to Xavier having achieved his goals is made in the subsequent episodes.
- Xavier's activities are related in "Spaceball".
- As of "The Super Scouts, Part I", Jamie is back at work at UBC.
- The saucer project is revealed in "The Super Scouts, Part II" and shown again in "Space Croppers".
- Just prior to "The Super Scouts, Part I"
- Briefly mentioned in "[Spaceball]]".
- Just prior to "Spaceball"
- Just prior to "Spaceball"
- Just prior to "The Night the Cylons Landed, Part I"
- "The Night the Cylons Landed" is specifically noted to occur on Halloween.
- Episode ends in the early hours of November 1.
- Just prior to "Space Croppers"
- Possible future revealed in "The Super Scouts, Part II".