How does a ship in Wildspace notice other ships while cruising?

Question

In the 5th edition version of Spelljammer, how do ships that are cruising (at a speed of 100 million miles per day, or about 1157.4 miles per second) notice other ships?

According to the Astral Adventurer's Guide (p. 21), while in the Astral Sea, creatures onboard need only think about possible ships near them:

One doesn't need a map to navigate the Astral Sea. Here, all creatures are blessed with directional awareness. In other words, a creature can get to where it wants to go by thinking of its destination, at which point it becomes aware of the most direct route to that location. The destination must be somewhere in the Astral Sea or in Wildspace, such as "the nearest githyanki outpost," "the astral dominion of Hestavar," or "Realmspace."

But, according to those same rules (p. 20), Wildspace at least appears to be separate from the Astral Sea:

Diagram 2.2 illustrates how the Astral Sea surrounds all the Wildspace systems, as well as the astral dominions of gods and the floating remains of dead gods (see the "Astral Dominions and Dead Gods" sidebar). [...]

• Is Wildspace considered part of the Astral Sea, and thus allowing navigation in the same manner? What about worlds within Wildspace?
• If not, is there some other method available to notice other ships while cruising, other than maybe the Wish spell?

I am mainly looking for 5e sourced rules and thoughts, but guidance sourced from prior editions is also helpful.

Answer 1

From 5E

This is the best we've got for 'noticing ships nearby' when in Wildspace

From the chapter on Astral Adventuring

A spelljamming ship automatically slows to its flying speed (discussed later in this chapter) when it comes within 1 mile of something weighing 1 ton or more, such as another ship

and that's...pretty much all we get. If you get within 1 mile of something big enough, your ship slows down. From there, you would presumably use normal Perception rules for spotting what slowed you down.

It is implied that you can track ships down in some fashion as, in the included adventure Light of Xaryxis...

A Star Moth locates and runs down the ship the party is on

But there is no mention of how they did it, and no mechanics laid out for how you could do it yourself.

We can presume that navigating in Wildspace is not thought driven because, again in Light of Xaryxis...

It becomes necessary to acquire a map of a particular system in order to be able to navigate it, or alternatively a magic item called a Wildspace Orrery that auto-creates such a map

So...we can pretty easily figure it's not thought driven and that you need to know where something is in Wildspace to get to it.

But that's pretty much all we get.

From AD&D 2E

So we go back to the original. And there's not much else to be had. The "get close to something and you slow down" rule is still in place. The only listed methods of locating ships that are beyond visual range are a pair of magic items:

Spelljammer Detector
When paired with a Helm of Liaison this roughly 40' long emplacement (typically installed on asteroids or other stationary bases) allows you to track the exact location of man-sized or larger object within 20,000 yards of the detector.

This rare, almost priceless item looks much like a huge insectoid face that stares blankly into the void of space. Commonly 40' long or more, and found on an asteroid or similar base, the detector shows the location of all man-sized or larger objects within a 20,000-yard radius (40 hexes). A helmet of liason is needed to link the detector to the wearer of the helmet. The helmet relays the information found by the detector in exact detail to the wearer.
When the helmet is put on, the wearer immediately gains a 360-degree sphere picture of the space around his base. Every minute detail can be seen in his mind. The positioning of these items chances as the base revolves, rotates, changes heading, etc. If there is a chance the user might lose an object being tracked, or that some significant detail might be missed, the user must make a Wisdom check.
Using the detector is nearly as fatiguing as manning a spelljammer helm, and is subject to the same requirements for resting afterwards.
The spelljammer detector (and a helmet of liason) might be purchased for 300,000 gp or more, depending upon availability and the reaction roll of the seller, but not for less. Additional helmets can be bought for 10,000gp each. The spelljammer detector can be used as long as a rested user is available.

-- War Captain's Companion, Book 1, Page 85

Sounder
This is a far more portable system with a much better range, but far less resolution. Depending on the model, it can locate any moving objects within range by speaking its command word. The weakest model having a range of 2,000 miles, the strongest with a range of 10,000 miles

Sounders come in an array of sizes; however, all of them are square and have a glass front. By looking into the sounder and speaking the command word, the user begins to hear a series of bleeps and witnesses wavy lines appearing on the glass. The sounder locates moving objects in wildspace and the phlogiston that are out of range of normal vision. The sounders' range varies with the device. There are four sounders, and those with the greater ranges cost more.

Sounder I - 2,000 miles. Sounder II - 4,000 miles. Sounder III - 8,000 miles. Sounder IV - 10,000 miles.
gp: 20,000, XP: 8,000

-- Krynnspace, Page 94

This makes sense, though.

As is occasionally commented on, in Spelljammer you're going FTL with tech from--at best--the 1600s. I would not expect it to be any easier to locate a ship that is beyond visual range in Spelljammer than it would be to do the same while in the ocean.

Answer 2

Wildspace is separate from the Astral Sea, both can be navigated alike

Wildspace is not part of the Astral Sea. Astral Adventurer's Guide, p. 4:

In Wildspace, the Material Plane and the Astral Plane overlap. Creatures and objects in Wildspace age normally and are effectively on both of those planes at once. If you were to leave your home world and continue outward until you neared the edge of your Wildspace system, you would begin to see a faint, silvery haze. By traveling into this haze, you pass from Wildspace into the Astral Sea (...)
Wildspace and the Astral Sea together comprise the Astral Plane.

A spelljamming helm allows you to navigate the ship at high speed whenever it is in space, such as when traveling through Wildspace or the Astral Sea:

You can use the spelljamming helm to move the ship through space, air, or water up to the ship's speed. If the ship is in space and no other objects weighing 1 ton or more are within 1 mile of it, you can use the spelljamming helm to move the vessel fast enough to travel 100 million miles in 24 hours.

At these speeds, there is little chance to notice other ships traveling, and 5e has no item for it. However, your ship will automatically drop down to normal encounter speed in an encounter, because if another ship is within 1 mile, you have an object weighing more than 1 ton in range.

Answer 3

The official rules don't say.

There seem to be no official rules for how to spot and intercept another ship, and the vast speeds and distances involved obviate nearly every option.

In my group's Spelljammer game, the DM described ships at cruising speed as leaving a sparkling trail like a comet's tail behind them, making them visible from across the vast distances as a line of light (with more detail visible through use of a spyglass, naturally, because aesthetic). Under that rule, noticing a ship at rest (or non-cruise speed) is virtually impossible across wildspace distances.

There's other issues, though. The only real reason you'd want to spot a ship in wildspace is if you want to intercept it, or be warned that it's intercepting you. And interception in Spelljammer is complicated by the fact that everyone goes the same speed in cruise mode. A pirate ship would have a chance of catching another vessel if they could spot a ship while it's coming closer and move to get in their path, thus forcing them out of cruise; but approaching from behind seems to be impossible since everyone maxes out at the same speed. The pirates would have to just chase after the target ship, getting no closer until it dropped out of cruise at its destination.

The alternative (which is used extensively in the Light of Xaryxis adventure) is to forgo spotting-and-intercept entirely -- instead, an aggressor can lurk around a larger body, such as a planetoid or asteroid field, and wait for ships to stumble into it so as to take advantage of the cruise-inhibiting mass effect.

And realistically, this method is also beneficial for a DM, as it ensures space battles happen in interesting environments. The alternative, two ships meeting in the void, is possibly the most boring way to run a ship-to-ship combat. (The seagoing equivalent would be getting jumped by pirates while weaving through the shoals around the Dry Tortugas, as opposed to having a fight in some anonymous stretch of the Atlantic.) This makes me suspect that the lack of spotting-and-intercept rules is intentional rather than an oversight, intended to nudge us towards the more exciting combat settings.