Observatory Quest

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

Talk to the assistant, then the professor to turn in each of the items. They will tell you the 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. Climb down the stairs, which leads to a maze-like dungeon. Each dead-end contains a chest. One of these chests contains the kitchen key (the location is different for every player), the other chests contain level 31 poison spiders, which can poison you for 3 damage, even if they miss. Keep searching the chests until you find the kitchen key. Go back to the ladder you entered the dungeon from and then go east, north, and then west and keep on going west until you see a level 1 goblin guard guarding a kitchen. WARNING: Once you prod him, he will turn into a level 42 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. Talk to the professor again and he will tell you to meet him at the other side of 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 southwest, and east a bit until you see another ladder. (Basically just follow the path until you reach the ladder, it shouldn't be that hard.)

Climb up the ladder, talk to the professor and watch the 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!

Reward

 * 2 quest points
 * 2,350 Crafting experience
 * 875 experience in Attack, Defence, Hitpoints, or Strength (random)
 * Depending on the astrological sign you see though the telescope, you will receive one of these items:
 * Maple longbow
 * Weapon poison
 * 3 law runes
 * Amulet of protection
 * Black two-handed sword
 * Super strength potion
 * 25 water runes
 * 3 tuna
 * Uncut sapphire
 * The Spirit of Scorpius, located in the graveyard north of the Observatory, will give you an unholy mould and bless unholy symbols for you.
 * Can talk to Historian Minas at the Varrock Museum to receive 5 Kudos