From the RuneScape Wiki, the wiki for all things RuneScape

Details

Walkthrough

Talk to the professor in the house near the Observatory and mention the observatory. He will tell you that the telescope is broken and refer you to his assistant.

The Assistant, working hard.

The assistant will ask you to collect some material for repairing the telescope:

• A bronze bar
• 3 planks
• A piece of molten glass
• 1 lens mould (this can be done during the quest)

The Lens Mould

Talk to the assistant, then the professor to turn in each of the items. They will tell you that they can't make a new lens because the goblins have stolen the lens mould.

Leave the house and head east to one of the abandoned buildings. There is a super anti-poison(1) respawn in the south east abandoned building. Take about two or three of those with you for when you encounter the poison spiders. Climb down the stairs in the west building, which leads to a maze-like dungeon. Each dead-end contains a chest. One of these chests contains the goblin kitchen key (the location is different for every player), the other chests contain nothing, a single dose of anti-poison or most likely a level 31 poison spider, which has around a 95% chance of poisoning you for 3 damage, even if the attack is blocked. Keep searching the chests until you find the kitchen key. Go back to the staircase you entered the dungeon from but do not exit the dungeon. Instead, go east, north, and then west and keep on going west until you see a level 1 sleeping guard guarding a kitchen. WARNING: Once you prod him, he will turn into a level 42 goblin guard. You have to kill him to get into the kitchen. Once you get into the kitchen, inspect the goblin stove. They have appeared to be using the lens mould as part of their cooking.

Head back to the professor. The professor will now ask you to make a lens for him. Do as he says by simply using the Molten glass with the Lens mould. Talk to the professor again and he will tell you to meet him at the other side of the observatory.

The Observatory

Head back down the stairs in the abandoned building you got the key/lens from. Take the northeast path, and follow it north, then west, then south-west, and east a bit until you see another set of stairs. (Basically just follow the path until you reach the stairs, it shouldn't be that hard.)

Climb up the stairs, talk to the professor and watch the long cut-scene of him fixing the telescope. Go up the stairs and talk to the professor again, he will tell you to have a look through the telescope. Talk to the professor after looking through the telescope. Tell him what constellation you saw to complete the quest and receive your reward!

Name	Picture
Aquarius
Aries
Cancer
Capricorn
Gemini
Leo
Libra
Pisces
Sagittarius
Scorpio
Taurus
Virgo

Reward

• 2 Quest Points
• 2,250 Experience
• An uncut sapphire (not the constellation reward)
• 875 experience in , , , or (random, it is also possible to receive no combat experience)
• Depending on the astrological sign you see though the telescope, you will receive one of these items:
  • Maple longbow (Sagittarius)
  • Weapon poison (Scorpio)
  • 3 law runes (Libra)
  • Amulet of defence (Cancer)
  • Black two-handed sword (Gemini)
  • Super strength potion (1)(Taurus)
  • 25 water runes (Aquarius)
  • 3 Fish pies (Pisces) (it can also happen that you will be rewarded with 3 tunas)
  • Uncut sapphire (Leo, Capricorn, Virgo, Taurus, Aries, Aquarius)
• The Spirit of Scorpius, located in the graveyard north of the Observatory, will give you an unholy mould and bless unholy symbols for you.
• You can talk to Historian Minas at the Varrock Museum to receive 5 Kudos
• Jug of wine - If players talk to the assistant after the quest, he will thank them for making his job easier and give them a drink.
• Ability to do Treasure Trails

After

Should a player look through the telescope again after the quest is completed they will see Scorpio. (No need to consult the star charts downstairs.) The Professor will then mention a book to be found downstairs. You will be sent to find Scorpius Grave. He will give you an unholy mould and request you return when you are worthy. Take the mould and a silver bar and make an unholy symbol. Then return to the grave so the spirit of Scorpius can bless the symbol.

Music

Music tracks unlocked:

Serenade

Trivia

• Two goblins -- Naghead and Wagchin -- due east of the ladder that leads to/from their camp—will be discussing gossip. Then, just at the juicy bit, one seems to notice you. It is a conversational loop, but amusing nonetheless. This is not dependant on the quest and may be experienced by any in the dungeon.

• There is a lost goblin wandering aimlessly around the dungeon trying to find his way out. He constantly exclaims about how confusing the tunnels are. Note:you can follow this goblin to reach any point(the beginning or end).

• The entrance to the Observatory Dungeon used to be at the quest starting house. It has been moved due to an update and now its located in the goblin village.