Why do we have eclipses in the heavens?
The moon spins around our planet each month. This monthly walk gives us the different Moon phases because we view the Moon's sunlit surface from different angles. This rotation is also the reason why the Moon gets between the Earth and the Sun and we experience New Moon or occasional Solar Eclipses, but also for the Earth to get between the Moon and the Sun and for us to experience Full Moon and occasional Lunar Eclipses. A more in-depth description of the phases can be found at https://en.wikipedia.org/wiki/Lunar_phase.
A reminder that nothing is forever...
Even though the Moon is majestic to view both with the naked eye and through a telescope in this periodic walk around our planet, the time I really experience awe is when eclipses occur. It's a reminder, that what we have, is not forever and that we cannot take anything for granted...not even that the Moon or Sun will shine in the heavens!
Lunar eclipses occurs when we are usually experiencing the Moon's full phase. When the Moon is full, the Earth is located directly between the Sun and Moon and we therefore can see the entire sunlit surface. Only at these special times, the Moon can hit bulls eye and be perfectly positioned to enter the (in astronomical scales) small shadow of our home planet.
Who will be able to see it?
Tonight, January 20-21, the inhabitants of Earth's who happens to experience night in this short period will be able to witness the total Lunar eclipse. To see if and when this occurs in your geographic location please refer to the excellent resource https://www.timeanddate.com/eclipse/lunar/2019-january-21. Generally, the Americas will have the best viewing point of this, but it will also be visible for parts Europe and western parts of Africa.
I encourage you to get out and experience this if you have clear skies. The next total Lunar eclipse will not happen until 2021, so don't miss out. Get out under the heavens and experience the awe of the Moon inside Earth's shadow.