Osteopenia refers to bone density that is lower than normal peak density but not low enough to be classified as osteoporosis. Bone density is a measurement of how dense and strong the bones are. If your bone density is low compared to normal peak density, you are said to have osteopenia.steopenia refers to bone density that is lower than normal peak density but not low enough to be classified as osteoporosis. Bone density is a measurement of how dense and strong the bones are. If your bone density is low compared to normal peak density, you are said to have osteopenia.
The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly (30 kpc) in diameter, and, on average, approximately 1,000 ly (0.3 kpc) thick.
On that scale with our Solar System in your hand, the Milky Way Galaxy, with its 200 â 400 billion stars, would span North America (see the illustration on the right). Galaxies come in many sizes. The Milky Way is big, but some galaxies, like our Andromeda Galaxy neighbor, are much larger. The universe is all of the galaxies â billions of them! NASAâs telescopes allow us to study galaxies beyond our own in exquisite detail, and to explore the most distant reaches of the observable universe.