Eclipses in general

Eclipses are named for the object (the sun or the moon) that is "blocked out" An eclipse occurs when the Sun, Earth and Moon are in alignment.

At first thought one might think that an eclipse should occur every month since the Sun, Earth and moon are in alignmnet during both the New moon phases and the Full moon phases.

 
Since the moon's orbit is tilted with respect to the Earth's orbit (the plane of the ecliptic) the Earth, Moon and Sun DO NOT line up in the right orientation to produce an eclipse every month.

While it is true that the moon is between the Sun and the Earth during a New Moon phase, they are not lined up in such a way as to allow the shadow of the moon to fall on the Earth, causing a Solar Eclipse.

Similarly, they ARE NOT in proper alignment to allow the Earth's shadow to fall on the moon, which would produce a lunar eclipse each month during the Full Moon phase.

Lunar Eclipses
    * Earth's Shadow is on the moon

    * Only occurs during the full moon phase

    * Earth is between the moon and the Sun

    * Moon must be in the right part of its tilted orbit.

    * Must be the right time of the day!

Lunar Eclipse GIF from Astronomy 161
Dr. Steven Gaunt University of Tennessee
 

Solar Eclipses

Solar Eclipse GIF from Astronomy 161
University of Tennessee
    * Moon's Shadow is on the Earth

    * Only occurs during the New Moon phase

    * Moon is between the Earth and the Sun

    * Moon must be in the right part of its tilted orbit.

    * Must be the right time of the day!
    Notice in the diagram above that there are two parts to the shadow of the moon cast upon the Earth.

    The larger, outer shadow is called the PENUMBRA. If you are on the part of the Earth that the penumbra passes over, you would see a partial solar eclipse.

    The narrower, darker shadow is called the UMBRA. Due to the distance and size of the moon, the maximum diameter of the umbra is 167 miles.

    As the Earth turns under the umbra it "draws" a line on the Earth called the Path of Totality. If you are on the part of the Earth that the path of totality passes over, you would see a TOTAL ECLIPSE of the Sun.
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