Jeremiah
Horrocks was born in the year 1618, the month and day is not exactly known.
Jeremiah’s father was James Horrocks, who was a watchmaker and his mother was
Mary Aspinwall. Jeremiah grew up in a small village three miles south of
Liverpool called Toxteth Park. Jeremiah attended college for three years at
Emmanuel College in Cambridge. While at Emmanuel College, Jeremiah met a
William Crabtree. They remained close friends and correspondents regarding
astronomy up until the death of Horrocks. Jeremiah graduated Emmanuel College
without a degree, but then taught himself astronomy.
Jeremiah
had a fascination with astronomy and put his life into it. His favorite
astronomers were Tycho and Kepler. Consequently, Jeremiah wanted to expand on
their observations. Horrocks was able to make observations of his own, correct
existing observations, and make his own theories. He corrected some planetary
constants used in equations. He was able to improve the lunar theory, studied
the tides and also planetary motion.
Horrocks
grew an interest in Kepler and his laws. After several years, Jeremiah was able
to prove that Kepler’s laws were correct. Horrocks observed another theory by
Kepler of celestial dynamics. Horrocks however didn’t completely agree with
this theory and made his own. Horrocks believed along with Kepler that the sun
moves the planets both by its rotation and by the emission of a quasi-magnetic
attractive force, which becomes weaker with distance and attracts the planets.
The specific shape of the planetary orbit is the result of a dynamic equilibrium
between a pushing force and a central force. However Horrocks contrasts by
saying, the planets orbit the sun in a falling orbital motion, much like how a
pendulum bobs back and forth. Contradicting Kepler, Horrocks believes that the
planets are always attracted to the sun and never repelled by it.
Horrocks
also had a contrasting theory with Kepler regarding gravity. He believed that
all the planets were also attracted to each other but since the Sun was the
most massive, it had the most influence on gravitation. Horrocks also believed
that comets follow an elliptical path around the sun.
Horrocks
was able to fix some of the other calculations made by previous astronomers
allowing him to get a glimpse of something never before viewed by any
astronomer. He calculated that solar parallax was 14’’, which was considerably
larger than Tycho’s 3’’ and smaller than Kepler’s 59’’. He then was able to
calculate that Earth’s orbit was 60,000,000 miles. Using these new
calculations, he made new calculations in the Rudolphine Tables, and made new calculations for velocities. Doing
all these new calculations enabled Horrocks to predict the Transit of Venus. And
the first Astronomer to do so. He looked at many different tables including
those of Kepler, in which he found another error. After fixing the error he
predicted that the Sun would appear going across the bottom of sun on December
4. Him and his friend William Crabtree both observed the transit of Venus and
took observational notes. These notes helped Horrocks predict more values including
the apparent diameter of Venus. They then went on to observe the Transit of
Mercury.
Another
important contribution to astronomy made by Horrocks is his lunar theory.
Horrocks looked again at Kepler’s theory about the moon and that it goes around
in an elliptical orbit, and that its inequalities are from the sun. He observed
all the phases of the moon, just like Tycho. His most famous discovery about
the lunar theory was regarding the second inequality of longitude, which he
says is due to variances in eccentricity and unequal motion of thee apsides.
This is an illustration of Jeremiah making calculations on Kepler theories.
This is a photo of the sun, Venus is the black circle crossing in the upper right corner
