3.what is significant about the tropic of cancer and tropic of capricorn?

These two "Tropics" are in fact two parallels, that is, circumferences belonging to Earths theoretical sphere surface, and parallel to the equator. They are the curves on which, on the solstice days, the Sun rays hit the Earth's surface perpendicular to it, along with Earth's rotation. Cancer Tropic is located at the North Emisphere, while Capricorn Tropic is on the South Emisphere. They are both at an angular distance of about 23°26' from the equator.

These two curves (circumferences, actually parallels) are the furthermost points from the equator where the Sun rays would ever reach the Earth's surface in a perpendicular way. For higher or lower latitudes (higher values of latitude's absolute value, be it towards the North or the South poles), Sun rays shall always reach Earth's surface obliquely, that is, by an angle lower than 90 degrees.

These two phenomena occur on:

The geographic surface between these two Tropics are called, in fact, the tropical areas, where seasons are not perceived and the Sun can be seen right above our heads (that is, at an elevation angle of 90°) at two specific moments within the year period (depending on the specific latitude).

This all phenomenom is caused by the tilt of the Earth's rotational axis with respect to its traslation plane around the Sun, which causes the existence of two solctices and to equinox every year.