Digital Universe Atlas

Digital Universe Guide

• Contents
• Overview
  • What is the DU?
  • Getting Help
  • Digital Universe License
  • Acknowledgments
• Getting Started
  • Installing
  • Launching the Milky Way
  • Learning to Fly Partiview
  • Partiview's User Interface
  • Digital Universe Files
• Milky Way Atlas
  • Overview
  • Tutorial
  • Data Groups
  • Optimizing
• Extragalactic Atlas
  • Overview & Primer
  • Tutorial
  • Data Groups
  • Optimizing
• Appendix
  • Light-Travel Time
  • Parallax and Distance
  • Redshift and Distance
  • Electromagnetic Spectrum
  • Constants and Units
• Index

• Home
• Digital Universe
• Guide
• Oort Cloud Sphere

The Stellar Distance Uncertainty

Models, Simulations, and Images

The Orion Nebula Model

Oort Cloud Sphere

The Oort cloud is a region of space surrounding the Sun where comets are believed to originate. Proposed by Jan Oort in the 1950s, the Oort cloud is believed to extend from 20,000 to 100,000 Astronomical Units (AU), with its greatest concentration around 50,000 AU (1 AU = 149 million kilometers = 93 million miles, the average Earth-Sun distance).

Comets are small, icy bodies that orbit the Sun. The most famous is Halley's Comet, which travels around the Sun in an eccentric orbit every 76 years. Comets were likely ejected from the Solar System once the planets formed. Jupiter, Saturn, Uranus, and Neptune's strong gravitational field likely ejected many comet-sized bodies out of the Solar System in random directions, where they settled into a cloud.

Occasionally, one comet in the cloud interacts with another or is perturbed by a passing star or a passing star's comet cloud. This could send the comet toward the Sun and planets, where it may enter into an eccentric, long-period orbit.

We represent the Oort cloud with a 50,000-AU-radius, wire-frame sphere representing the location of the central concentration. Fifty thousand astronomical units is equal to about 10 light-months, which is 0.8 light-years, or 4.8 trillion miles. Keep in mind, though, that the Oort cloud is 80,000 AU thick and imagine a similar sphere around each star in the Atlas. Would any two overlap? Of course, stars of different luminosities would have Oort clouds of differing size, or even no Oort cloud at all, but visualizing the Oort cloud allows us to see the possibility of stars interacting.

The Oort cloud is the last outpost of our Solar System. Beyond it is the gas of the interstellar medium through which the Sun, planets, and comets move as they orbit the Galaxy once every 225 million years.