Why does a planet in a circular orbit have a changing velocity even at constant speed?

Its direction of motion is continually changing

What does a star form from?

A nebula (cloud of dust and gas)

The balance between gravity pulling inwards and the outward pressure from fusion

The galaxy is moving away from us

The cosmic microwave background (CMB) radiation

It explodes as a supernova, leaving a neutron star or black hole

12questions. Pick an answer and you'll see why right away.

Which object is at the centre of our Solar System?
Which is the correct order of the first four planets from the Sun?
Which model of the Solar System places the Sun at the centre?
Why does a planet in a circular orbit have a changing velocity even at constant speed?
What happens to an astronaut's mass on the Moon compared with on Earth?
What does a star form from?
What keeps a main-sequence star stable?
What is the final stage of a star about the size of the Sun?
What does red-shift of light from a distant galaxy show?
What does the red-shift of galaxies provide evidence for?
Which evidence makes the Big Bang the accepted model rather than the Steady State theory?
What is the fate of a star much more massive than the Sun?