Solar System & Astronomy help please :)?
Question:
Also, when an astronomer says "universe" what is he talking about? Apparently it means different things when different people say it.
Answer:
The Sun's diameter is 864,938 miles (1,391,980 km). This is about 109 times as big as the Earth. The volume of the Sun is 1,299,400 times bigger than the volume of the Earth; about 1,300,000 Earths could fit inside the Sun.
Source:
http://www.enchantedlearning.com/subject...
The Milky Way galaxy contains over 200 billion stars. Our sun is just one of those stars. As you can imagine, the galaxy is extremely large and it would be almost impossible to explain how small the earth is in comparison to it.
Source:
http://imagine.gsfc.nasa.gov/docs/ask_as...
The universe refers to all that is in "space"; including all of the galaxies. Here is a good, easy-to-read article about it:
http://imagine.gsfc.nasa.gov/docs/ask_as...
The Earth has a mass of 6*10^24 kg and a radius of 6.4*10^6 m.
The Sun has a mass of 2*10^30 kg and a radius of 7*10^8 m.
I believe that, when most people refer to "universe," they mean the entirety of space.
try this site
http://www.planetpals.com/planetsize.htm...
And when they say universe, they are talking about EVERYTHING! Hard to understand, but thats what they mean...everything
This is a good link for size comparison.
http://www.astronomynotes.com/chapter1/s...
When astronomers talk about Universe, they mean one thing, it is all the physical space with all its energy and matter. The Universe is everything. What is different is the theories about the size, the shape, if it is expanding or not and so on.
I'll assume you have a feel for how big the Earth is. The sun can hold about 1 million earth sized planets.
The universe is usually defined as "everything that we can observe and beyond". It is so big that it is referred to as "infinite", which means without end. Since we have yet to detect the edge of the universe, infinite will have to do.
i don't remember
The distance around the sun is 342 times bigger than the distance around the Earth's equator. If the Earth were a marble, the sun would be like a school bus.
The Milky Way is the galaxy that our sun is in. It has about 300 billion suns. The sun is a pinprick too small to comprehend inside the galaxy.
The universe usually refers to everything we can observe or deduce through observation. The milky way galaxy is, again, a pinprick too small to comprehend within the universe.
Radius Density
Sun 695000 1.99e30
Earth 6378 5.97e24
As a galaxy, the Milky Way is actually a giant, as its mass is probably between 750 billion and one trillion solar masses, and its diameter is about 100,000 light years.
Now it gets Tricky
The term universe has a variety of meanings based on the context in which it is described.
In materialist philosophical terms, the universe is the summation of all matter that exists and the space in which all events occur which has an equivalent idea amongst some theoretical scientists most noted Brackus Mons known as the total universe. In cosmological terms, the universe is thought to be a finite or infinite space-time continuum in which all matter and energy exist. (It has been hypothesized by some scientists that the universe may be part of a system of many other universes, known as the multiverse.)
The terms known universe, observable universe, or visible universe are often used to describe the part of the universe that can be seen or otherwise observed by humanity. Because cosmic inflation removes vast parts of the total universe from our observable horizon, most cosmologists accept that it is impossible to observe the whole continuum and may use the expression our universe, referring only to that knowable by human beings in particular.
However, the observable universe, consisting of all locations that could have affected us since the Big Bang given the finite speed of light, is certainly finite. The edge of the cosmic light horizon is 13.7 billion light years (4.19 Gpc) distant. The present distance (comoving distance) to the edge of the observable universe is larger, due to the ever increasing rate at which the universe has been expanding; it is estimated to be about 78 billion light years (7.8 × 1010 light years, or 7.4 × 1026 m). This would make the volume, of the known universe, equal to 1.9 × 1033 cubic light years (assuming this region is perfectly spherical). The observable universe contains about 7 × 1022 stars, organized in about 100 billion galaxies, which themselves form clusters and superclusters. The number of galaxies may be even larger, based on the Hubble Deep Field observed with the Hubble Space Telescope. The Hubble Space Telescope discovered galaxies such as Abell 1835 IR1916, which are over 13 billion light years from Earth.
And to further confuse us, recently, "universe" has become plural--"universes". I'm not sure of what that means, for to me a universe includes EVERYTHING.
Any input from fellow astronomers on this subject will be appreciated.
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