Jeremiah Horrocks

Jeremiah Horrocks (1618–1641) was an English astronomer who made significant contributions to the study of the solar system. Despite his short life, he achieved what many before him could not—he accurately predicted and observed the 1639 transit of Venus. His work helped improve the understanding of planetary motion and paved the way for future astronomers like Isaac Newton.

Early Life and Education

Jeremiah Horrocks was born in 1618 in Toxteth, a small village near Liverpool, England. He came from a modest family, and little is known about his early childhood. His father was likely a watchmaker or farmer, and his family could not afford an elite education.

Despite these challenges, Horrocks displayed a deep interest in mathematics and astronomy from an early age. He was largely self-taught, reading books by famous astronomers like Johannes Kepler, Tycho Brahe, and Galileo Galilei.

At the age of 14, he entered Emmanuel College at the University of Cambridge. During his time there, he studied classical subjects, including Latin and Greek, but his true passion was astronomy. He read Kepler’s Rudolphine Tables and Copernicus’ heliocentric theory, which proposed that the Earth revolved around the Sun.

Astronomical Work and Discoveries

Challenging Kepler’s Calculations

Kepler’s laws of planetary motion were groundbreaking, but they were not perfect. Kepler had predicted that Venus would not pass directly in front of the Sun in 1639. However, Horrocks, through careful calculations, realized that Kepler’s planetary tables contained errors.

Horrocks improved the calculations and predicted that Venus would transit the Sun on November 24, 1639 (Julian calendar, December 4 in the modern calendar). This was a remarkable discovery, as transits of Venus are rare astronomical events that occur in pairs, eight years apart, with over a century between each pair.

The 1639 Transit of Venus

Horrocks prepared for the event by setting up a simple but effective observation method. He used a telescope to project the image of the Sun onto a piece of paper, allowing him to see Venus as a small black dot moving across the Sun’s surface.

On the predicted day, Horrocks observed the transit from his home in Much Hoole, Lancashire. He recorded the event in great detail, confirming that Venus did indeed pass in front of the Sun. His friend and fellow astronomer, William Crabtree, also observed the transit from Manchester.

Horrocks’ observations were groundbreaking because:

1. They proved that Kepler’s predictions needed adjustments.

2. They provided accurate data to refine the size and orbit of Venus.

3. They helped estimate the scale of the solar system more precisely.

Estimating the Distance Between the Earth and the Sun

Horrocks also attempted to calculate the Astronomical Unit (AU), which is the distance between the Earth and the Sun. Before his time, many estimates were wildly inaccurate. Using his transit observations, Horrocks proposed that the Sun was about 95 million kilometers (59 million miles) away from Earth—a vast improvement from earlier estimates, though still lower than the modern value of 149.6 million kilometers (93 million miles).

Scientific Approach and Writing

Horrocks documented his findings in a book titled Venus in Sole Visa (Venus Seen on the Sun), in which he described his observations and provided calculations to correct Kepler’s planetary tables.

His work emphasized the importance of precise measurements and systematic observations, principles that would later become fundamental in modern science.

Untimely Death and Legacy

Tragically, Horrocks died in 1641 at the age of just 22. The cause of his death remains unknown, but it is believed to have been due to illness. His early death meant that many of his ideas remained unpublished during his lifetime.

However, his contributions were not forgotten. After his death:

• His manuscript Venus in Sole Visa was published by astronomer Johannes Hevelius in 1662, ensuring his work reached future generations.

• His findings inspired later astronomers like Edmond Halley, who used transits of Venus to measure the size of the solar system more accurately in the 18th century.

• Horrocks is now recognized as one of the pioneers of modern observational astronomy.

Impact on Modern Astronomy

Horrocks’ work laid the foundation for later astronomical discoveries. His careful observations and mathematical methods influenced Isaac Newton, who developed the law of universal gravitation.

Today, Horrocks is honored in various ways:

• The Horrocks Observatory in Preston, England, is named after him.

• A lunar crater and an asteroid (3078 Horrocks) are named in his memory.

• He is often credited as the father of British astronomy due to his contributions at such a young age.

Conclusion

Jeremiah Horrocks was a brilliant astronomer whose passion for science led to one of the most important discoveries of the 17th century. His prediction and observation of the 1639 transit of Venus changed the course of astronomy. Despite his early death, his work influenced future scientists and helped shape our understanding of the solar system.

His story is a testament to the power of curiosity, dedication, and scientific inquiry.