Archivum Data Disc

Quest chain:

1. Archivum Data Disc - Started from Archivum Data Disc - Dropped by killing Molgeim or Steelbreaker last in the Iron Council ecounter.
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3. The Celestial Planetarium
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5. • Hodir's Sigil - Defeat Hodir on his hard mode
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   • Thorim's Sigil - Defeat Thorim on his hard mode
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   • Freya's Sigil - Defeat Freya on her hard mode
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   • Mimiron's Sigil - Defeat Mimiron on his hard mode
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7. Algalon - Recieve the Celestial Planetarium Key which allows the entire raid acces to Algalon once Yogg-Saron has been killed.
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9. Kill Algalon to be able to get All is well that ends well.

Spoiler alert, Text that is said after inserting the Data Disc.

Brann Bronzebeard says: Now, this is what we call a nice find!
Archivum System says: Entry denied. Access level insufficient.
Brann Bronzebeard says: I'll show ye access, ye wretched machine. Here it is again: Norgannon's key!
Archivum System says: Access to the Archivum granted. Intrusion protection mechanisms suspended.
Brann Bronzebeard says: Looks just like all the other titan archives me lads have found... only older... and bigger.
Brann Bronzebeard says: Wait a second: this doesn't look right! Next to this blinking light... what's this Algalon signal?
Archivum System says: Initiating query. The Algalon Failsafe is an automated emergency signal following a Prime Designate's demise.
Brann Bronzebeard says: Prime Designate? Where have I 'eard that before? By my grandfather's beard, Loken is Azeroth's Prime Designate. Loken's death triggered this!
Archivum System says: Affirmative. Timestamp of Prime Designate Loken's destruction coincides with signal activation.
Brann Bronzebeard says: Well? Who's on the listening side of the signal? What's going to happen?
Archivum System says: Searching... Destruction of Prime Designate is considered the first warning sign of systemic planetary failure. Algalon observer entity's arrival is followed by planetary diagnostics resulting in one of two possible reply signals. Reply-code Alpha, signaling "All is well" and Reply-code Omega, signaling planetary re-origination.
Brann Bronzebeard says: Planetary re-origination? Speak plainly, ye blasted machine!
Archivum System says: The decomposition of the planet and its living organisms into base elements: metals, rocks, gases. This is followed by a period of reconstitution of each element into the original planetary blueprint.
Brann Bronzebeard says: Hear that, lads? It's only the end of the world! Well, what are ye waiting for, ye rusty machine? Initiate Reply-code Alpha. All is well! Pints are on me!
Archivum System says: Request denied. Reply-codes built into Algalon observer entity. He is both messenger and message.
Brann Bronzebeard says: Well, what's this Algalon going to be looking for with his diagnostics? What are our chances?
Archivum System says: Algalon diagnostics assess danger of systemic Old God corruption in planetary vital functions. Calculating chance of Omega Reply-code...
Archivum System says: Ninety-nine point nine nine percent.
Archivum System says: That's repeating, of course.
Brann Bronzebeard says: Blast it, lads. Looks like we've got a fight ahead of us.

Unlocking the Celestial Planetarium

1. 
   
2. Complete I Choose You, Steelbreaker or I Choose You, Runemaster Molgeim, enabling one Archivum Data Disc to drop (it is not party loot; similar to Key to the Focusing Iris).
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4. Accept the quest from the disc and bring it to the Archivum Console, located beyond the Assembly of Iron.
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6. After listening to the Archivum Console speak, accept the quest The Celestial Planetarium from Prospector Loren. Locate the Celestial Planetarium and return to Prospector Loren.
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8. This enables four quests to obtain the watchers' sigils, which may be performed in any order:
   
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   • Freya's Sigil - Complete Knock, Knock, Knock on Wood.
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   • Hodir's Sigil - Complete I Could Say That This Cache Was Rare.
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   • Mimiron's Sigil - Complete Firefighter.
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   • Thorim's Sigil - Complete Lose Your Illusion.
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10. Complete all four quests to enable the quest Algalon from Prospector Loren.
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12. Simply speak to the Archivum Console to complete the quest, rewarding Celestial Planetarium Key.