Astrophysics &Cosmology Flashcards

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1
Q

Astronomical Units (AU)

A

Earth to the Sun 1.496 x 1011 metres ~1.5 x 1011 metres

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2
Q

Parsecs (pc)

A

3.086 x 1016 metres ~3.1 x 1016 metres (1 AU)/tan⁡〖 (( 1)⁄(3600 ))〗

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3
Q

Light-Years (ly)

A

9.461 x 1015 metres ~9.5 x 1015 metres

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4
Q

Hubble’s Law

A

The speed of recession of a galaxy is directly proportional to its distance from Earth.

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5
Q

Critical Density

A

A density level above which the universe will head back to a “Big Crunch”.

The fate is summarised as: ρo = constant x Ho2.

Density > ρo – universe is closed, the crunch is coming.

Density < ρo – universe is open, expands forever.

Density = ρo – universe is flat, expands forever but the rate reduces to zero after infinite time.

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