Moon Size, Universe Size and everything in between | Explained

Описание: The Size of the Moon, the Sun, the Stars and the Galaxy | Explained

The Moon is one of the most significant objects in the night sky, second only in brightness to the Sun. So, how big is the Moon?
The diameter of the Moon is only 3,474 km across. Just for comparison, the diameter of the Earth at the equator is 12,756 km. That’s only 27% the diameter of the Earth. The Moon is also the 5th largest moon in the Solar System, after Ganymede, Titan, Callisto and Io. In terms of volume, the Moon only contains 2.195 x 1010 km3.

That sounds like a lot of cubic kilometers of Moon, but again, that’s only 2% the volume of Earth. The surface area of the Moon is 3.793 x 107 km2. That’s about the same size as Russia, Canada and the United States combined. The circumference of the Moon is 10,921 km. Again, that’s only a little over a quarter the circumference of the Earth.

How big is our Sun?
Another thing worth considering is the fact that our Sun is pretty small, as stars go. As a G-type main-sequence star (specifically, a G2V star), which is commonly known as a yellow dwarf, its on the smaller end of the size chart (see above). While it is certainly larger than the most common type of star – M-type, or Red Dwarfs – it is itself dwarfed (no pun!) by the likes of blue giants and other spectral classes How big are the Stars?

An example of a larger star than our Sun is the blue supergiant Rigel in the constellation Orion. This is a star with 17 times the mass of the Sun, which puts out 66,000 times as much energy. Rigel is estimated to be 62 times as big as the Sun. Bigger? No problem. Let’s take a look at the red supergiant Betelgeuse, also in the constellation Orion. Betelgeuse has 20 times the mass of the Sun, and it’s nearing the end of its life; astronomers think Betelgeuse might explode as a supernova within the next 1,000 years.

But the biggest stars in the Universe are thought to be the monsters VY Canis Majoris, and UY Scooti. These red hyper and super giant stars are thought to be more than 1,800 times the size of the Sun.

The Milky Way Galaxy

The Milky Way is our home galaxy, the spot where the Earth resides. We are not anywhere near the center — NASA says we’re roughly 165 quadrillion miles from the galaxy’s black hole, for example — which demonstrates just how darn big the galaxy is.

So how big is it, and how does it measure up with other neighborhood residents? The numbers are pretty astounding. NASA estimates the galaxy at 100,000 light-years across. Since one light year is about 9.5 x 1012km, so the diameter of the Milky Way galaxy is about 9.5 x 1017 km in diameter. The thickness of the galaxy ranges depending on how close you are to the center, but it’s tens of thousands of light-years across.

Our galaxy is part of a collection known as the Local Group. Because some of these galaxies are prominent in our sky, the names tend to be familiar.

The Milky Way is on a collision course with the most massive member of the group, called M31, or the Andromeda Galaxy. The Milky Way is the second-largest member, with M33, known as the Triangulum Galax, the third-largest, Andromeda appears much brighter in the night sky due to its size and relatively closer distance.

There are about 30 members of this group. Because we are inside the Milky Way’s arms, it appears as a band of stars (or a fuzzy white band) across the Earth’s sky. Casting a pair of binoculars or a telescope across it shows a mix of lighter areas and darker areas; the darker areas are dust that obscures any light from stars, galaxies and other bright objects behind it. From the outside, however, astronomers say the Milky Way is a barred spiral galaxy — a galaxy that has a band of stars across its center as well as the spiral shape.

Based on observing globular clusters (star clusters) in the galaxy, astronomers have estimated the Milky Way’s overall age at 13.5 billion years old — just 200 million years younger than the rest of the universe. Kalirai’s group’s research indicates that the Milky Way formed in the following sequence: the halo (including globular star clusters and dwarf galaxies), the inner halo (whose stars were born as a result of this construction) and the outer halo (created when the Milky Way ate up nearby ancient dwarf galaxies).

Meet Laniakea, Our Home Supercluster

Our cosmic address extends well beyond Earth, past the Milky Way and toward the farthest reaches of the universe. But now astronomers are adding another line: the Laniakea Supercluster, which takes its name from the Hawaiin term “lani” meaning heaven and “akea” meaning spacious or immeasurable. And the name is true to its meaning. The supercluster extends more than 500 million light-years and contains the mass of 100 quadrillion Suns in 100,000 large galaxies. This research is the first to trace our local supercluster on such a large scale.