Navigating under a starless sky: how to determine the position?

Question

My alternate Earth is placed, together with the whole solar system and nothing else, in the center of the Boötes void.

At nearly 330 million light-years in diameter (approximately 0.27% of the diameter of the observable Universe), or nearly 236,000 $Mpc^3$ in volume, the Boötes void is one of the largest-known voids in the Universe, and is referred to as a supervoid.

According to astronomer Greg Aldering, the scale of the void is such that "If the Milky Way had been in the center of the Boötes void, we wouldn't have known there were other galaxies until the 1960s."

Assuming a human-like species evolves on this planet, what can they use to determine their position on the globe, when the compass has not yet been invented? As a reference, consider the level of knowledge of some early seafarers like the Phoenicians.

Answer 1

Who needs stars to navigate, anyway?

Navigation can be done by means other than stellar wayfinding. Consider the various methods in use by the Polynesians:

• They used concept maps that show patterns in the water
• They used patterns of waves & currents
• They used cloud patterns, winds and the movements of birds
• They used songs and stories to record and describe sea routes
• They also used stars, but those are lacking in your locale! However, I've heard that there are at least 60 galaxies within the Void, strung along in a kind of tubular structure. Perhaps one or more of those will be visible.

Your navigators could very easily fashion highly detailed route maps that note currents, wave patterns, shoals, coastal features. These could be in the form of strip maps which show only what's along a route, not the whole world or even a broad region:

Answer 2

With NO stars, but also with no navigational tools such as compass or sextant?

Owch!

The best you could do is to determine your Latitude, and East-west-north-south directions, by using a sun stick.

Obviously you need to do this in the daylight, with a visible sun and a reasonably stable workspace.

While it is trivial to get compass direction this way, latitude is a bit more tricky because of seasons and the Earth's tilt.

You need to know how far the sun deviates from true vertical at noon, for a given date of the calendar. By measuring the angle of the sun's shadow at noon (by observing the ratio of stick height to shadow length), you can derive a very accurate latitude.

Longitude is a LOT more difficult. To have any chance of determining your longitude(east-west positions on the globe), you need to know when the sun rises or sets. Accurate to a few seconds. You also need to know the elapsed time since taking a matching baseline for this at a known location. This requires a timekeeping tool that is accurate to seconds, over however long a period you need to navigate away from your base. This was simply not available in Phoenician times. Nor in Roman times, nor even in Medieval times. The first practical timepiece for ship navigation was made in the 1800's

But you do not need to know your place on the globe, to navigate. Line of sight works perfectly, and also line of sight to a recognizable feature on a map. With a good enough map you can sail as far as the shore is within sight. And panic yourself to death if a nice fog rolls in, and you lose orientation. Or in the case of this benighted little planet, if the sun sets and the moon is not in a visible location.

Answer 3

Expert knowledge of coastal features

It's entirely reasonable to not know where you are when on open water and, only attempt navigation when you have sight of the coastline. This means limited ocean crossings, but that's equally not unreasonable. Ocean crossings didn't become a common thing until relatively recently in the grand scheme of navigation. Even then they didn't have accurate positioning until very late in the game, even that only working at certain times of day.

Let's specifically consider the Phoenicians as you refer to them in the question. They basically coast hopped the Mediterranean. If that's the technology you want, that's the limitation you get. Keep the land to port, or the land to starboard, depending which way you're going on the route. It helps if you know whether you're on the north or south coast of the sea, but that at least you can tell from the sun.

Answer 4

The Phoenicians only knew how to determine north and their latitude. For this purpose you only need the Sun; at noon it will give you true north, and its height above the horizon, combined with the date, will give you your latitude.

This is all the Phoenicias knew how to determine, anyway.

With an accurate chronometer, the Sun at noon can also give your longitude; but accurate chronometers only came some 2,000 years after the Phoenicians went the way of the Dodo.

Answer 5

If they have several fast-moving moons, or moons of nearby planets that are large enough to be visible with the naked eye or a small telescope on an unstable platform, then they can navigate better than Earth’s mariners could until the 20th century. They can use ephemerises giving the positions of the moons to determine the absolute time, which combined with their measurement of the time and height of the sun at local noon will give them their longitude as well as their latitude. If the moons are too small and faint to be visible by day, they will need something that keeps time well enough to measure the time between local noon and their first chance to see the moons in the night sky — for each minute that measurement is out by, their longitude will be out by a quarter of a degree.

Answer 6

Sun is almost enough by day.

And by night, if the night is dark enough, you will see a lot of features that can replace the Sun - as zodiacal light and gegenschein.

Looks not that hard.

Answer 7

It is just a bet... but, maybe, you could find directions like ants:

https://www.sciencedirect.com/science/article/pii/S0960982212009323

https://link.springer.com/article/10.1007/s10071-020-01431-x

And there is a theory some ants/birds can see (I mean literally see) the earth's electromagnetic field.

People from your alternate Earth can been born with similar sense. Other option is then found a "crystal" that they can see THROUGH it and see the electromagnetic waves. Vikings may have done some thing close:

https://www.nationalgeographic.com/news/2011/11/111111-vikings-sunstones-crystals-navigation-science/

Answer 8

I am not a scientist, so maybe I am wrong, or misunderstood something here, but I think they can still use the sun or moon's position to navigate or determine their position. At least, based on OP's comments, I assume that they still have a sun and moon like Earth's.

Here are some links that explain it better:

From: https://en.wikipedia.org/wiki/Celestial_navigation

From: https://www.tgomagazine.co.uk/skills/how-to-use-the-sun-to-navigate/

Using the sun to hold a bearing

This technique uses the sun or moon to keep you heading in the right direction. It doesn’t replace the use of a compass, but instead helps you to maintain a certain route. Using the sun, or at night the moon, gives you a reference to the cardinals of the compass.

1. Face the direction (bearing) you are going to travel and reach out with your arm as if you were going to grab hold of the sun and hold this position for a couple of seconds: this helps imprint your orientation to the sun.
2. Lower your arm and move forward, keeping in mind where the sun should be in relation to you.
3. You can travel for 10 mins on a single bearing using this technique before you need to repeat it.
4. If the sun is behind you, use your shadow. Reach out and hold your arm parallel with your shadow and hold this position for a couple of seconds.

Using this technique frees you up from having to constantly refer to your compass or map and instead allows you to concentrate on your surroundings and enjoy the scenery. Mountain rescue dog handlers routinely employ this method so they can concentrate on their dog and visibly search the area themselves.

Angular measurement

Accurate angle measurement evolved over the years. One simple method is to hold the hand above the horizon with one's arm stretched out. The width of the little finger is an angle just over 1.5 degrees elevation at extended arm's length and can be used to estimate the elevation of the sun from the horizon plane and therefore estimate the time until sunset. The need for more accurate measurements led to the development of a number of increasingly accurate instruments, including the kamal, astrolabe, octant and sextant. The sextant and octant are most accurate because they measure angles from the horizon, eliminating errors caused by the placement of an instrument's pointers, and because their dual mirror system cancels relative motions of the instrument, showing a steady view of the object and horizon.

Navigators measure distance on the globe in degrees, arcminutes and arcseconds. A nautical mile is defined as 1852 meters, but is also (not accidentally) one minute of angle along a meridian on the Earth. Sextants can be read accurately to within 0.2 arcminutes, so the observer's position can be determined within (theoretically) 0.2 miles, about 400 yards (370 m). Most ocean navigators, shooting from a moving platform, can achieve a practical accuracy of 1.5 miles (2.8 km), enough to navigate safely when out of sight of land.

Using a marine sextant to measure the altitude of the sun above the horizon

Latitude Latitude was measured in the past either by measuring the altitude of the Sun at noon (the "noon sight"),

Lunar distance Main article: Lunar distance

The older method, called "lunar distances", was refined in the 18th century and employed with decreasing regularity at sea through the middle of the 19th century. It is only used today by sextant hobbyists and historians, but the method is theoretically sound, and can be used when a timepiece is not available or its accuracy is suspect during a long sea voyage. The navigator precisely measures the angle between the moon and the sun, or between the moon and one of several stars near the ecliptic. The observed angle must be corrected for the effects of refraction and parallax, like any celestial sight. To make this correction the navigator would measure the altitudes of the moon and sun (or star) at about the same time as the lunar distance angle. Only rough values for the altitudes were required. Then a calculation with logarithms or graphical tables requiring ten to fifteen minutes' work would convert the observed angle to a geocentric lunar distance. The navigator would compare the corrected angle against those listed in the almanac for every three hours of Greenwich time, and interpolate between those values to get the actual Greenwich time aboard ship. Knowing Greenwich time and comparing against local time from a common altitude sight, the navigator can work out his longitude.