Astrophysics &Cosmology Flashcards
1
Q
Astronomical Units (AU)
A
Earth to the Sun 1.496 x 1011 metres ~1.5 x 1011 metres
2
Q
Parsecs (pc)
A
3.086 x 1016 metres ~3.1 x 1016 metres (1 AU)/tan〖 (( 1)⁄(3600 ))〗
3
Q
Light-Years (ly)
A
9.461 x 1015 metres ~9.5 x 1015 metres
4
Q
Hubble’s Law
A
The speed of recession of a galaxy is directly proportional to its distance from Earth.
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.