The nebular hypothesis doesn't have a specific "formation date" like a historical event. It's a scientific theory that explains how solar systems form, and it's been evolving over time as new observations and evidence have been gathered.

Here's a breakdown:

* Initial Concepts: Ideas about the formation of the solar system were around long before the term "nebular hypothesis" was coined. For example, Immanuel Kant in the 18th century proposed a theory of a spinning cloud of dust and gas collapsing to form a star and planets.

* Modern Nebular Hypothesis: The modern nebular hypothesis, as we understand it today, was developed in the 19th century, particularly by Pierre-Simon Laplace.

* Evolution of the Theory: This hypothesis has been refined and expanded over the past century, incorporating insights from observations of other star systems and advances in astrophysics.

Therefore, you can't pinpoint a specific date for the "formation" of the nebular hypothesis. It's a continuously developing scientific idea that's been around for centuries and continues to be refined.

The key takeaway is that the nebular hypothesis explains how our solar system, and likely others, formed billions of years ago, but the theory itself has evolved over time.