Why aren't there eclipses every month?

Why aren't there eclipses every month?






   We all know that when moon comes between the sun and the Earth, it casts it's shadow on the Earth, better know by its name, a solar eclipse. Similarly, a lunar eclipse occurs when the Earth casts it's shadow on the moon. For more info some of you might also know that solar eclipses occur on new moon days and lunar eclipses on full moon days.

  But hey! That's something everybody's knows. So, by logic, if the moon takes about a month to orbit the Earth, shouldn’t we get an eclipse every two weeks? First a solar eclipse, and then two weeks later, lunar eclipse, back and forth? Think logically and you will wonder the same. 

  The moon revolves around the Earth causing different phases of moon due to different part of Earth's shadow casted on it. Two such interesting phases are full moon and new moon. Now, when moon is fully under Earth's shadow, it's a new moon day (or a no moon day for pessimists!). But wait, isn't that the same condition for a lunar eclipse? But then, new moon day is every month. So why isn't lunar eclipse every month? And same is with solar eclipse.

  Well, that would have been the case if the moon was perfectly aligned with the Earth's plane. It turns out that the moon is 5° tilted from the perpendicular. 

  Imagine the solar system as a flat plane. Now the moon is not on this plane, it is 5° above or below it depending on the position of the Earth. It aligns with the plane every 4 times a year, when the Earth is on the 4 of the positions of a plus sign in its orbit.

  For those who got it, great. But for those whose still can't visualise, watch the video below:


  Bottom line: If the Earth and moon orbited on the same plane around the sun, we’d have a total solar eclipse – and a total lunar eclipse – every month. But we don’t, because the moon’s orbit is inclined to Earth’s orbit by about 5.14°. 
Old Post

Sharing is caring!

Post a Comment

To track replies to your comment, click the 'Notify Me' checkbox

Previous Post Next Post

Contact Form