Even with the most advanced technology, we only see a small part of the Universe. It is called the observable Universe, and it is the part of the Cosmos whose light has had time to reach us.
The observable Universe is shaped like a sphere, with the Earth at its center. So we can see the same distance in all directions.
The limit of the observable Universe is called cosmic light horizon. The objects located on that horizon are the furthest we can see. His light departed towards us almost since the origin of the Universe, 13.7 billion years ago. So we see them as they were more than 13,000 million years ago. That is why they are so important to know the evolution of the Universe.
But, as the Universe expands, in reality those objects are much further. Currently, they are already 46,500 million light years.
|Hubble||Visible, ultraviolet and near infrared light|
Great NASA observatories
To explore the entire observable Universe, NASA orbited four space telescopes: Hubble, Chandra, Compton and Spitzer. Each one captures a different type of light. Currently, Compton is no longer operational.
The universe visible to the naked eye
The part of the Universe that we see with the naked eye is called celestial sphere. It is an imaginary sphere, with the Earth in the center, where the constellations are located. It reaches up to 2.5 million light years.
The furthest that can be seen is the neighboring Andromeda galaxy, and the two satellite galaxies of the Milky Way: the Small and the Large Magellanic Cloud. Everything else belongs to our galaxy, the Milky Way.
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|Structures of the Universe||Types of particles in the Universe|