Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

Reason of lanthanoid contraction is :

What are the main consequences of lanthanoid contraction ?

Give an explanation for the following observation : The gradual decrease in size (actinoid contraction) from element to element is greater among the actinoids than that among the lanthanoids (lanthanoid contraction).

What are lanthanoids ? Explain lanthanoid contraction.