Navigating in the 1700's - ships relied on a combination of traditional techniques and emerging scientific advancements

In the 1700s how did ships navigate?

In the 1700s, ships relied on a combination of traditional techniques and emerging scientific advancements to navigate the open seas. Here are the main methods they used:

1. Dead Reckoning

• Dead reckoning was the primary method of navigation, where sailors would estimate their position based on a previously known location. They would record their speed (estimated by a log-line or chip log), direction (measured with a compass), and time traveled. However, this method was prone to accumulating errors over time, especially during long voyages.

2. Compass

• The magnetic compass was essential for determining direction. By aligning the compass with the magnetic north, sailors could maintain a consistent course, though compasses were sometimes affected by magnetic deviation or errors in calibration.

3. Celestial Navigation

• Sextant: Introduced in the mid-18th century, the sextant allowed sailors to measure the angle between a celestial body (usually the sun or stars) and the horizon. This measurement, known as an altitude, helped calculate latitude.

• Latitude: Latitude was easier to determine than longitude. Sailors could determine latitude by measuring the angle of the North Star (Polaris) or the sun at noon above the horizon. This told them how far north or south they were.

• Ephemeris: Navigators used published ephemerides (astronomical tables) to understand the positions of celestial bodies on specific dates and times.

4. Longitude Problem

• Determining longitude (east-west position) was one of the greatest challenges of 18th-century navigation. It required an accurate timepiece or advanced astronomical knowledge.

• Lunar Distance Method: Sailors could estimate longitude using the lunar distance method, which involved measuring the angle between the moon and another celestial body (like a star). This complex process required detailed tables and calculations but was in use before the introduction of precise timekeeping.

• Marine Chronometer: In 1761, John Harrison developed the marine chronometer, a highly accurate clock that could keep precise time at sea. With this, sailors could compare the local time (determined by celestial observation) with the time at a known reference point, such as Greenwich, to calculate longitude. The marine chronometer revolutionised navigation, but it wasn’t widely adopted until later in the century.

5. Lead Line (Sounding)

• Ships used a lead line to measure the depth of the sea. A lead weight attached to a line marked with fathoms would be dropped to the seafloor. By knowing the depth, navigators could avoid underwater hazards and estimate their proximity to land, especially when approaching coastal areas.

6. Portolan Charts and Nautical Maps

• Portolan charts (detailed coastal maps) and other nautical charts were used for navigation, particularly near coasts. These maps included information about ports, coastlines, hazards, and compass roses to help sailors plot their course.

7. Logbooks

• Sailors meticulously recorded their navigational data, such as courses, speed, position estimates, and any celestial observations, in logbooks. These records were crucial for dead reckoning and for tracking progress during long voyages.

Despite these methods, navigation was still difficult and dangerous. Many ships were lost due to poor navigation, storms, or miscalculations. However, the invention of tools like the sextant and marine chronometer in the 1700s marked the beginning of a new era in maritime navigation, leading to more accurate and reliable voyages across the world’s oceans.

Hang on, the North Star Moves?

The North Star, or Polaris, is not perfectly fixed in the sky but appears relatively stationary due to its position close to the North Celestial Pole. Here’s a more detailed explanation of how it works:

1. Polaris and the North Celestial Pole

• Polaris is located near the point in the sky where Earth’s axis of rotation (the North Celestial Pole) points, so it appears almost directly above the Earth’s North Pole. As a result, it remains nearly stationary in the northern sky while other stars appear to rotate around it due to the Earth’s rotation.

• While it is not exactly at the North Celestial Pole, it is close enough that for most practical navigational purposes in the 1700s (and even today), it was treated as a fixed reference point for determining latitude in the Northern Hemisphere. Sailors would measure the altitude (angle) of Polaris above the horizon to determine how far north or south they were. This angle corresponds roughly to the observer’s latitude.

2. Slight Movement of Polaris

• Polaris does move slightly because it is not exactly at the North Celestial Pole; it’s about 0.7 degrees away. Over the course of the night, as the Earth rotates, Polaris traces a small circle in the sky. However, this movement is very small, so it was considered a reliable reference for navigation.

• Additionally, over long time scales (thousands of years), Polaris’ position in the sky changes because of axial precession—the slow wobble of Earth’s rotational axis. In ancient times, different stars were near the celestial pole, and eventually, Polaris will no longer be the North Star. But in the 1700s, Polaris was already in a similar position to where it is today, making it highly useful for sailors.

3. Other Stars for Navigation

• In the Southern Hemisphere, sailors couldn’t use Polaris because it is not visible from there. Instead, they relied on other celestial bodies like the Southern Cross (Crux) or used different methods of celestial navigation.

In summary, while Polaris moves slightly, for 18th-century navigators, it was close enough to the celestial pole to be a very stable and practical point of reference for determining latitude in the Northern Hemisphere.

What's the Longitude and Latitude of the Southern Cross?

The Southern Cross (Crux) is a prominent constellation in the Southern Hemisphere used for navigation, particularly before modern instruments were available. While constellations don’t have a single “latitude” or “longitude” like a fixed point on Earth, each of the stars in the constellation has a specific declination (equivalent to celestial latitude) and right ascension (equivalent to celestial longitude).

The approximate celestial coordinates of the four main stars in the Southern Cross:

Main Stars of the Southern Cross (Crux):

1. Acrux (Alpha Crucis): The brightest star in the constellation.

• Right Ascension: ~12h 27m

• Declination: ~−63° 5′

2. Mimosa (Beta Crucis): The second brightest star.

• Right Ascension: ~12h 48m

• Declination: ~−59° 41′

3. Gacrux (Gamma Crucis): The third brightest star, at the top of the cross.

• Right Ascension: ~12h 31m

• Declination: ~−57° 7′

4. Delta Crucis: Forms the right arm of the cross.

• Right Ascension: ~12h 16m

• Declination: ~−58° 45′

Celestial Coordinates:

• Right Ascension is measured in hours, minutes, and seconds, similar to longitude on Earth. It describes how far a star is along the celestial equator.

• Declination is measured in degrees, like latitude, and tells how far a star is from the celestial equator, either north or south.

Using the Southern Cross for Navigation:

• The Southern Cross points roughly towards the South Celestial Pole, which is useful for determining the direction of true south. A line drawn from the long axis of the cross (from Gacrux to Acrux) can be extended to approximate the position of the South Celestial Pole in the sky.

Navigators in the Southern Hemisphere used this constellation to find south, just as Polaris was used in the Northern Hemisphere to find north. However, unlike Polaris, the Southern Cross does not sit exactly at the celestial pole but helps point toward it.

What's the Longitude and Latitude of the North Star ?

Polaris, the North Star, is located near the North Celestial Pole and has specific celestial coordinates, which are similar to the concepts of longitude and latitude used on Earth. In celestial navigation, these coordinates are right ascension (RA) and declination (Dec).

Current Celestial Coordinates of Polaris:

• Right Ascension (RA): ~2h 31m 49s

• Declination (Dec): ~+89° 15′ 51″

Explanation of Celestial Coordinates:

• Right Ascension (RA): This is similar to Earth’s longitude, measured in hours, minutes, and seconds. It indicates how far a star is along the celestial equator, from a reference point (the vernal equinox). Polaris’ right ascension places it roughly 2 hours away from this point.

• Declination (Dec): This is similar to Earth’s latitude, measured in degrees, indicating how far north or south a star is from the celestial equator. Polaris’ declination is very close to +90°, meaning it sits nearly directly above Earth’s North Pole.

Polaris’ Position in the Sky:

• Polaris is located about 0.7 degrees from the North Celestial Pole. Although it is not perfectly aligned, this is close enough that for most practical purposes, it appears stationary in the night sky and can be used as a reliable reference point for finding true north.

• Due to Earth’s axial precession (a slow wobble in Earth’s axis over thousands of years), Polaris won’t always be the North Star. About 14,000 years from now, the star Vega will take its place near the North Celestial Pole.

Polaris’ near-fixed position in the northern sky has made it extremely valuable for navigators in the Northern Hemisphere, especially before the advent of modern navigation technology.

A simple map showing the positions of Polaris (North Star) and Acrux (Southern Cross) on a celestial coordinate grid. The x-axis represents right ascension (similar to longitude), and the y-axis represents declination (similar to latitude). Polaris is close to the North Celestial Pole, while Acrux is in the southern sky near the South Celestial Pole.

This map helps visualise how these stars are positioned in the sky relative to each other in terms of celestial coordinates. 

The following map now includes the approximate position of England, marked in green. This illustrates how England, Polaris (North Star), and Acrux (Southern Cross) relate to each other in terms of celestial coordinates. While England is positioned at a relatively northern latitude (~51.5° N), Polaris is much closer to the North Celestial Pole, and Acrux is far to the south, below the celestial equator. 

The following map now includes Sydney (marked in purple) along with England, Polaris, and Acrux. Sydney’s position, with a latitude of around 34° S, places it in the Southern Hemisphere, below the celestial equator. You can see how Sydney is much closer to Acrux (Southern Cross) compared to England, which is nearer to Polaris (North Star), reflecting their positions on Earth and their respective view of the night sky. 

The following map shows Navigating from Sydney to England, show cross-over point using Acrux then polaris.

Navigating from Sydney to England by using celestial navigation (in the era before modern tools) involves a process of gradually switching reference stars. In the Southern Hemisphere, sailors would rely on Acrux (Southern Cross), and as they move northwards, they would begin to lose sight of Acrux and start to use Polaris (North Star).

The cross-over point—where sailors would stop using Acrux and begin to rely on Polaris—occurs near the equator, where neither Polaris nor Acrux are reliably visible.

Here’s a step-by-step breakdown:

1. Starting in Sydney (Southern Hemisphere)

• In the Southern Hemisphere, sailors would use Acrux and the other stars of the Southern Cross to find their direction. Extending the long axis of the Southern Cross points toward the South Celestial Pole, which helps determine south.

2. Crossing the Equator

• As sailors move northward from Sydney, they would eventually reach the equator, around 0° latitude. At this point, neither Acrux nor Polaris are directly overhead; they both would be low on the horizon or not visible. This is the crossover point.

• Around the equator, sailors would start relying more on celestial navigation techniques such as dead reckoning, compass readings, and daytime navigation using the Sun until they could reliably see Polaris.

3. Moving Toward England (Northern Hemisphere)

• As they continued northward, Polaris would gradually rise higher in the sky, while Acrux would disappear below the southern horizon.

• By the time sailors reached higher northern latitudes (closer to England), Polaris would become their primary navigational star, since it remains almost directly above the North Pole.

The Crossover Latitude

The crossover point typically happens around 10-15° north of the equator, where Acrux sinks below the horizon, and Polaris becomes visible. This is the point where sailors would switch from using the Southern Cross to Polaris as their guide for navigation.

Now, let’s plot a visual representation showing the navigational crossover from Sydney to England. I’ll mark the general location of the equator as the crossover point between using Acrux and Polaris.

This plot shows the navigation journey from Sydney to England, with the crossover point marked in orange at the equator. As sailors traveled northward, they would switch from using Acrux (Southern Cross) for navigation to using Polaris (North Star) when they crossed this region around the equator. This helps visualize the transition between southern and northern hemisphere navigation techniques based on the visibility of these stars. 

Using the Flat Earth representation

When applying a flat Earth representation to navigation, the concept of celestial navigation becomes quite different from the conventional model used on a spherical Earth. On a flat Earth, celestial bodies such as the stars, sun, and moon are often thought to revolve around the Earth in a circular pattern, rather than appearing in the sky due to the Earth’s rotation around its axis.

Here’s how we could adapt the navigation concept using Polaris, Acrux, and a flat Earth map:

1. Polaris in the Flat Earth Model:

• In flat Earth representations, Polaris is typically depicted as directly above the North Pole, and it stays fixed in the sky.

• As a result, on a flat Earth map, Polaris would always be visible to observers in the Northern Hemisphere. The farther south you travel, the lower Polaris appears in the sky, and eventually, it disappears below the horizon.

2. Acrux in the Flat Earth Model:

• In contrast, Acrux and other southern stars would be visible only from southern locations. These stars are generally thought to revolve in circles around the flat Earth disk, and their visibility decreases as you move northward, with Acrux disappearing below the horizon as you approach the Northern Hemisphere.

3. Crossover Point on a Flat Earth:

• The crossover point in this case would occur somewhere on the equator (around the middle of the flat Earth map). As you move from Sydney (Southern Hemisphere) toward England (Northern Hemisphere), you would gradually lose sight of Acrux and eventually gain sight of Polaris.

• On a flat Earth map, the equator would be represented as a circular boundary around the inner regions (closer to the North Pole). As you move across this boundary, you switch between visibility of the Southern and Northern stars.

Visualising This on a Flat Earth Map:

In a flat Earth representation, I would place Polaris at the center (above the North Pole), and the positions of Sydney, England, and the equator would be spread out in concentric circles. Acrux would be located in the southern sky, revolving around the outer edges of the flat Earth model.

Let me now create a basic flat Earth map illustrating the positions of Sydney, England, Polaris, Acrux, and the crossover point.

North Star is visible from both London and Sydney

This map illustrates a flat Earth representation of navigation from Sydney to England, with the following key elements:

• Polaris (North Star) is located at the center of the map, representing the North Pole in the flat Earth model.

• Sydney and England are plotted at their approximate positions based on latitude and longitude.

• Acrux (Southern Cross) is shown near the outer edge, representing its location in the southern sky, visible from the Southern Hemisphere.

• The equator (marked as an orange dashed circle) represents the crossover point where sailors would stop using Acrux and begin using Polaris as they move northward from Sydney toward England.

In this flat Earth model, celestial navigation involves transitioning between these stars as sailors cross the equator. 

This updated flat Earth map now includes Buenos Aires (marked in cyan), along with Sydney, New York, England, Polaris, and Acrux. Buenos Aires is located in the Southern Hemisphere, like Sydney, making Acrux visible from both locations. The equator remains the crossover point, where celestial navigation would shift from using Acrux to using Polaris as sailors move from the Southern to the Northern Hemisphere.

This representation helps visualise how different stars would be used for navigation depending on the location, even in a flat Earth model. 

Seems the Flat Earth Representation allows navigation from all points without the need for complex calculations.