The thickness of the disk of the Milky Way is around 3,000 light-years. In our s
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The thickness of the disk of the Milky Way is around 3,000 light-years. In our scale, how thick is the Milky Way? The galaxy has a bulge at its center. The bulge is spherical in shape with a diameter of 10,000 light-years. How big is the bulge in our scale? Draw a circle to represent the bulge at the appropriate location on your drawing. Calculate the diameter of the Solar System in this scale. The diameter of our solar system (out to the Oort cloud) is about 1 ly. Mark the location of the Solar System on your scaled down drawing of the Milky Way at the appropriate location.Explanation / Answer
34.If our solar system was the size of a coffee cup, the Milky Way Galaxy would be the size of the North American Continent.
Since ancient times people have speculated about the nature of the hazy band of light that stretches around the entire sky. It is widest and brightest in the summer sky, especially in Sagittarius. There is a long twisty dark lane through Cygnus known as the Great Rift. In autumn the path winds north past Cassiopeia and Perseus, in winter past Orion, and in Spring it reaches down to the Southern Cross.
Our galaxy appears to be in the shape of a big pancake with a bulge in the middle. Our solar system is embedded inside the pancake about half way between the edge and the middle. When we try to look out along the edges we see the combined light of billions of stars. Most of those stars are too far away to pick out individually but together they add up to a milky haze.
Our galaxy is about 100,000 light years across. The central bulge is about 16,000 light years thick. The thinner region where our solar system resides is about 3000 light years thick. Our solar system orbits around the core once every 200 million years. The total number of stars in the Milky Way is probably several hundred billion.
The core of our galaxy lies in the direction of Sagittarius. We have detected that stars in that region are circling the center at very high speed. The simplest explanation for why those stars can travel so fast without flying completely out of the galaxy is that there is a supermassive black hole in the core. The mass of the black hole is estimated at 3 to 4 million times the mass of the Sun.
The disk and central bulge are only the obvious parts of the galaxy; the parts that glow in the dark. There is also a part that we can't see with our eyes but can be detected by other means, directly and indirectly. We can directly measure light outside the range of human eyes, such as infrared and ultraviolet. We can also deduce where mass exists by its gravitational effect on other objects. We have concluded that the visible disk of the galaxy is surrounded by a huge sphere of material we call the halo.
One of the very visible populations in the halo is the globular clusters. These are the oldest objects made out of stars in the Universe. The globulars formed long before the birth of galaxies. When the galaxies came along, the globulars were caught by the gravity and have been orbiting around them ever since. There are about 200 globular clusters orbiting in the halo of the Milky Way.
35.
The Milky Way is a large barred spiral galaxy comprising an estimated 200 billion stars (some estimates range as high as 400 billion) arrayed in the form of a disk, with a central elliptical bulge (some 12,000 light-years in diameter) of closely packed stars lying in the direction of Sagittarius. It is surrounded by a flat disk marked by six spiral arms that project from a dense, elongated concentration of stars, or bar, that runs through the bulge—four major and two minor—which wind out from the nucleus like a giant pinwheel. Our sun is situated in one of the smaller arms, called the Local or Orion Arm, that connect the more substantial next inner arm and the next outer arm. The sun lies roughly 27,000 light-years from the center of the galaxy, and in the galactic plane. When we look in the plane of the disk we see the combined light of its stars as the Milky Way. The diameter of the disk is c.100,000 light-years; its average thickness is 10,000 light-years, increasing to 30,000 light-years at the nucleus.
Certain features of the region near the sun suggested that our galaxy resembles the Andromeda Galaxy. In 1951 a group led by William Morgan detected evidence of spiral arms in Orion and Perseus. Another bright arm stretches from Sagittarius to Carina in the southern sky. With the development of radio astronomy, scientists have extended a nearly complete map of the spiral structure of the galaxy by tracing regions of hydrogen that dominate the spiral arms. The development of telescopes that could be placed in orbit led by 2005 to confirmation that the Milky Way was a barred spiral galaxy, not a spiral one as had been believed.
Surrounding the galaxy is a large spherical halo of globular star clusters that extends to a diameter of about 130,000 light-years; this is called the stellar halo. The galaxy also has a vast outer spherical region called the corona, or dark halo, which is as much as 600,000 light years in diameter and, in addition to dark matter which accounts for most of the Milky Way's mass, includes some distant globular clusters, the two nearby galaxies called the Magellanic clouds, and four smaller galaxies.
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