Many of the stars in a galaxy have planets. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe.įurther observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way, which is one of a few hundred billion galaxies in the observable universe.

Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day. According to this theory, space and time emerged together 13.787 ☐.020 billion years ago, and the universe has been expanding ever since the Big Bang.

The Big Bang theory is the prevailing cosmological description of the development of the universe. The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. Observable universe: 8.8 ×10 26 m (28.5 G pc or 93 G ly) The Hubble Ultra-Deep Field image shows some of the most remote galaxies visible to present technology (diagonal is ~1/10 apparent Moon diameter)

Marker dead space