Because we live in the Northern Hemisphere, the solar rays will never be perfectly overhead (at the zenith). Instead, the solar rays will always strike us at an angle, which means our shadow will always be visible. As shown in the figure above, our shadows will always point in some direction northward (northwest in the morning to northeast in the evening). 

In the Northern Hemisphere, our shadow length will always be the longest in the winter months because of solar rays' low angle of incidence (sun is lower in the sky during the winter months). During the summer months, the sun is higher in the sky, so our shadows are shorter.

On June 21, the sun's most direct rays strike the Tropic of Cancer (23.5°N). This is the official start of summer in the Northern Hemisphere (longest day of the year). In the Southern Hemisphere, however, this is the official start of winter (shortest day of the year).

On December 23, the sun's most direct rays strike the Tropic of Capricorn (23.5°S). This is the official start of summer in the Southern Hemisphere (longest day of the year). In the Northern Hemisphere, however, this is the official start of winter (shortest day of the year).

A solar eclipse can occur if a new moon is perfectly aligned and casts a shadow on Earth. People in the umbra will experienced a few minutes to darkness during the day. 

A lunar eclipse can occur if Earth is in between the sun and a full moon. Earth will cast a shadow on a full moon, causing the moon to become red in color. Note that the moon will still be visible because some sunlight is still being reflected off the moon's surface.

An incoming high tide leads to rush of water flowing towards land (flood current). Approximately 6 hours later (a quarter of Earth's rotation), an impending low tide results in the water rushing seaward (ebb current).

The relative position of the sun and moon affects tidal changes. When the graivtational forces line up, they combine to pull water towards it, resulting in a high tide for locations at these tidal bulges. At locations that don't receive this pull, a low tide event occurs. Note that there are two high tide events and two low tide events every day.