The Greenwich Meridian is in the wrong place

Summary

In this video, the host explores the Greenwich Observatory in London, discovering that the Prime Meridian line, which defines zero longitude for GPS, has moved from its original location. Through a dramatic reenactment and discussions with Steve Mold, they explain the historical and technical reasons behind the shift, including the transition from star-based to Earth-based measurements. The video also humorously addresses the impact on tourists and the complexities of defining 'up' and 'zero' on a spherical Earth, ending with a plug for the host's new book, 'Love Triangle'.

Takeaways

• 📍 The speaker is at the Greenwich Observatory in London discussing the Prime Meridian, which is the reference line for zero degrees longitude.
• ⛲ The Prime Meridian's original location was determined by the placement of a telescope's eyepiece, which has since moved slightly from its historical position.
• 🌧 The script humorously mentions the typical rainy British Spring weather during the visit to the observatory.
• 📱 GPS devices show a small inaccuracy when pinpointing the exact location of the Prime Meridian, with the speaker's device showing -0.1 degrees.
• 🎬 A dramatic reenactment by 'Steve mold' is mentioned to illustrate the confusion of tourists when their GPS does not show exactly zero at the Prime Meridian.
• 🔭 The script explains that the historical method for determining the Prime Meridian involved observing stars and their transit times across a telescope's eyepiece.
• 🌟 The Prime Meridian was originally based on the celestial observation of stars, but this method was later replaced by Earth-based measurements due to inaccuracies.
• 🌍 The Earth's rotation and its orbit around the Sun are discussed as factors that affect the definition of a day and the need for sidereal time measurements.
• 🕰 The importance of accurate timekeeping for determining longitude is highlighted, with a mention of Harrison's clocks and the transition from solar to sidereal time.
• 📚 The speaker mentions a book about trigonometry and the inaccuracies in the historical definition of the Prime Meridian, which was corrected in the 20th century.
• 🎁 The script ends with a promotion for the speaker's book, 'Love Triangle', and an offer for pre-order bonuses, including a virtual bookmark with a personalized touch.

Q & A

What is the significance of the Prime Meridian at the Greenwich Observatory?

The Prime Meridian at the Greenwich Observatory defines the zero point for longitude. It is the reference line from which all other longitudes are measured, and it helps in determining the exact location of a place on Earth.

Why was the Prime Meridian line moved from its original position?

The Prime Meridian line was moved because the original definition of 'up' used for astronomical observations was not perfectly aligned with the Earth's center of mass. As technology advanced, it was necessary to redefine the line to improve accuracy in global positioning systems.

How does the Earth's shape affect the determination of the Prime Meridian?

The Earth's spherical shape makes it challenging to define a fixed point for longitude. The Prime Meridian is determined not just by a physical line, but by a series of observations and measurements that account for the Earth's rotation and its position in space.

What is the role of the telescope in defining the Prime Meridian?

The telescope at the observatory is used to observe stars and determine the exact time they pass over a specific point, which helps in calculating the longitude. The alignment of the telescope with the stars is crucial for accurate timekeeping related to the Prime Meridian.

Why is the term 'solar time' not ideal for measuring the Earth's rotation?

Solar time is based on the Earth's position relative to the Sun, which is not a perfect measure because the Earth also moves around the Sun while rotating. This results in a slight discrepancy, making sidereal time, which is based on the Earth's rotation relative to the stars, a more accurate measure.

How did the historical use of a Zenith tube contribute to the inaccuracies in the Prime Meridian's original location?

The Zenith tube, which was used to point directly upwards, relied on local gravity to level a mercury mirror. However, local gravity does not perfectly align with the Earth's center of mass, leading to slight inaccuracies in the timing of star observations and thus the position of the Prime Meridian.

What was the international agreement in 1884 regarding the Prime Meridian?

In 1884, an international agreement was reached at a conference where countries decided to adopt the Prime Meridian at the Greenwich Observatory as the global zero point for longitude to standardize timekeeping and navigation.

How did the advent of satellite technology influence the redefinition of the Prime Meridian?

The introduction of satellite technology allowed for more precise measurements of the Earth and its features. This led to the realization that the original astronomical observations used to define the Prime Meridian were slightly off, prompting a redefinition based on Earth's center of mass.

What is the current method for defining the Prime Meridian?

The current method for defining the Prime Meridian is based entirely on Earth's center of mass, using geodetic measurements from satellites and other advanced technologies, rather than astronomical observations.

Why is the discrepancy between the old and new Prime Meridian locations only about 100 meters?

The discrepancy is minimal because the original definition was already very close to accurate. The slight adjustment of about 100 meters was made to align the Prime Meridian with the Earth's center of mass, improving the accuracy of global positioning systems.

What is the significance of the book 'Love Triangle' mentioned in the script?

The book 'Love Triangle' is a publication by the same author who discusses the complexities of the Prime Meridian and other related topics. It provides a deeper understanding of the subject matter and is promoted as a resource for further reading.