How to unlock the sundial
To access the The Sundial activity, you must first complete a quest called A Matter of Time. You can pick up this quest from Ikora in the Tower after watching the Season of Dawn intro cutscene. She'll ask you to search for Osiris on Mercury, and soon after you land on the planet and fight your way through grunts from the Red Legion, you'll find him.
Osiris will then ask you to head to the Tangled Shore. Here you will need to collect the Sundial components by killing Cabal, which can be easily found near Sorik's Cut. Using solar damage can cause several Cabal components to drop and in turn speed up your progress, so it's a good idea to replace weapons and subclasses with Solar. Not only will you get the fun stuff going faster, but you'll also have the chance to see some of the Solar Subclass tweaks that have been made for Season of Dawn.
After collecting the necessary components, head to Thieves's Landing and drop the sundial components at the Obelisk. Next, you'll need to collect Orbs of Light, get Ability Kills, and get Super Kills to fill a progress bar. Look for Public Events to quickly reload your Super, or use Master Weapons to make the process a little easier. Once you've done that, return to the Obelisk and drop the Light. Then return to Mercury and visit Osiris. It will unlock the sundial for you, and you can find it on the Mercury map in the upper right corner.
This is a six-player in-match activity with a recommended power level of 850, and it will give you this season's artifact, the Lantern of Osiris, on your first success.
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