Answer to Question 1
A collapsing cloud of gas does not form a single star. Because of instabilities, the cloud breaks into fragments, producing perhaps thousands of stars. A stable group of stars that formed and are held together by their combined gravity is called a star cluster. In contrast, a stellar association is a group of stars that formed together but are not gravitationally bound to one another. The stars in an association drift away from each other in a few million years.
Answer to Question 2
On a clear winter night, you can see with your unaided eye the Great Nebula of Orion as a fuzzy wisp in Orion's sword. With binoculars or a small telescope it is striking, and through a large telescope it is breathtaking. At the center lie four brilliant blue-white stars known as the Trapezium, the brightest of a cluster of a few hundred stars. Surrounding the stars are the glowing filaments of a nebula more than 8 pc across. Like a great thundercloud illuminated from within, the churning currents of gas and dust suggest immense power. The significance of the Orion Nebula lies hidden, figuratively and literally, beyond the visible nebula. The region is ripe with star formation.
Betelgeuse star (Hubble)
The difference between mieosis and mitoses
The same star field photographed with (a) a ground-based telescope, which is subject to poor seeing
Spectra of a Metal-Poor and a Metal-Rich Star
For the circuit in Figure 1, assume ideal diodes. The peak inverse voltage is approximately
Smooth Brittle Star.