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Glossary

This page is meant to make it easier for you to understand the content of this web site. The glossary contains both astronomical and art terms.


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Eccentricity: A value which describes an orbit. The lower the eccentricity, the closer the orbit is to being a perfct circle.

Eclipse: A celestial event in which a body appears in front of another, blocking the light of the one furthest away. The most known kinds of eclipses are when the moon passes in front of the sun, or when the earth passes in front of the sun, colouring the moon red/orange.

Eliptical galaxy: A galaxy classification in the Hubble scheme, ellipticals get their names from their shape. The ellipticals are classified by their degree of ellipticity as they appear to the observer. E0 types are completely spherical, and E7 types are very elliptical (i.e., elongated). E1 through E7 have increasing degrees of ellipticity. They are smooth and structureless, and contain mainly old Pop. II type stars.

Envelope: The outer, less dense layer of a star. Link: stellar structures.

Escape velocity: The velocity required to escape from an object. The earth has an escape velocity of about 11 km/s, which means that you need to travel faster than 11 km/s to break free from earth. A black hole has an escape velocity of more than 300 000 km/s, which makes it impossible to escape, even for light.

Event horizon: A boundary dividing space into a region that can be seen from one that cannot. In the case of a black hole, it is that surface surround the region out of which light itself cannot escape. No signal or information from within the event horizon can reach the outside universe.







 




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