The Stargazing Room is located within The Noble Tavern. There are two tabs in the lower right to show which tab you are on.
Background: A Mysterious female stargazer frequents the secret room at The Noble Tavern. No-one knows the name of this stranger or from whither she comes, but her prophecies never lie. It is said that her crystal ball is magical. Rub it gently, and the desires of your heart will be revealed and come true.
Guide:
1. Diamonds or Star Cards can be used to stargaze. Players are able to acquire heroes, artefact fragments and legendary gear by stargazing.
2. There is a chance to acquire a significant amount of diamonds when stargazing.
3. New heroes are added and removed from the prize pool daily. Newly added heroes will remain there for 2 days.
Changing the Stargazing Hero:
In the upper left, you can click the change hero icon. From there it will let you select from a list of heroes available for Stargazing. The list changes every 24 hours, but only appears to be Ascended Tier Heroes, and I have yet to see a Celestial or a Hypogean available.
Cost: It costs either 1 Stargazer Card (which are earned from spending real money on in-game packages) or 500 Diamonds to activate the Stargazer in which you will click the device and shortly receive your prize.
Probability (located bottom left of screen): There are the current odds as of 8/10/2019 I am sure they will change over time.
Selected Hero: 2% (Math shows this can be costing you 25,000 gems to get the selected hero.)
30,000 Diamonds: 0.01% (Math shows this can be costing you 5 Million gems.)
Mythic Gear x1: .84% (.07% per Gear, of the 12 gear currently available.)
Artifacts Fragment x1: 24.5% (3.5% per Artifact, which currently is 7.)
Rare Enchantment Token x1 (worth 1,000 enhancement points): 4.5%
Arena Ticket x2: 5.01%
Elite Hero Card x1: 3.2% (.8% for each faction)
Large Crate of Gold x2 (24 hours of AFK each): 4.5%
Large Crate of Hero EXP x1 ( ?? hours of AFK each): 4.5%
Large Crate of Hero's Essence x2 (8 hours of AFK each): 4.5%
Rare Hero Card x1: 9% (2.25% for each faction)
Small Pile of Gold x5 (6 hours of AFK each): 9.36%
Small Pile of Hero EXP x2 (?? hours of AFK each): 9.36%
Small Pile of Hero's Essence x5 (2 hours of AFK each): 9.36%
Common Enhancement Tokens x50 (10 enhancement points each): 9.36%
Strategy:
Star Cards: For those who spend money in the game, here is a fun little way of getting some random stuff with your purchase. Mythic gear, heroes, and the coveted 30,000 gems are all on the line! I would use them as you get them and hope you are lucky. The only reason to wait on using your Star Card is to make sure you have a hero you want in that slot. It may only be 2%, but if you end up getting someone you aren't wanting you will be upset, so use at the right time.
Gem Use: For newer players, I would advise spending your gems on opening hero packs at The Noble Tavern. While the rewards from the Stargazer seem amazing, you really will have more benefit on just buying 10 packs for now. Once you are a bit more weathered and the allure of gambling is more your style, then step on up. Most of these items are based on your auto-farming rates, while others are better obtained with patience. I feel that shooting for the big prize of 30,000 should be your goal, but know the odds. As I explained above the odds are so low that you could purchase 90 heroes from The Noble Tavern in packs of 10. While this doesn't guarantee the hero you want, it does give you 90 points on the Hero Choice card which lets you pull an epic from your faction of choice. Any shot paying with gems is a gamble, please know that. I don't want you all heartbroken.
My thoughts: I feel this is a mechanic that is targeted mainly at those spending their real money on the game. Which is always a good thing to support the developers. I feel they didn't want to make it so that people who don't or can't spend money miss out on this feature. So take it as you will, but please know the odds.