Today is a lunar eclipse, a penumbral lunar eclipse to be more precise. It begins at 4:22 pm EST and ends at 9:13 pm EST. The peak is 6:49 pm EST and is best viewed in Europe and Africa.
Lunar eclipses occur on the full moon (purnima) and are of three types: total, partial and penumbral. A total lunar eclipse is when the Moon entirely passes through the earth's dark shadow orumbra, which means "shaded area." (Our word "umbrella" comes from the latin root, "umbra"). A partial lunar eclipse is when the Moon partially passes through the umbra. A penumbral lunar eclipse is when the Moon passes outside the umbra in a region called the penumbra, which means "almost shaded area." The penumbra receives some partial rays of the Sun, which makes the penumbral lunar eclipse the weakest of the three types and is very difficult to detect, even with a telescope. About 35% of lunar eclipses are of the penumbral type, while about 30% are partial eclipses which can easily be seen with the naked eye. 35% or so are total eclipses, which are the most dramatic and intense from an astrological point of view.
Why isn't there a lunar eclipses every month on the full Moon? This is because the Moon's orbit around the earth is at a 5 degree tilt relative to the Earth's orbit around the Sun. Only 2-4 times per year is the Moon's orbit within the plane of the Earth's orbit. The points where the Moon's orbit and the Earth's orbit cross one another are the eclipse points known as Rahu and Ketu, the North and South nodes of the Moon.
Because the nodes of the Moon are so mysterious and unusual in nature their influences cause abnormal functioning to whatever planet they aspect. During the eclipse the nodes of the Moon are aspecting both of the personal planets, the Sun and Moon and are cutting off their normal functioning. They create an opening in our psyches for subtle energies to enter, either positively or negatively. It's therefore best to do spiritual practices during eclipses and not anything of significance in the material world like having a surgery, or signing an important document. Eclipses are excellent times for meditation, chanting mantras, or other spiritual practices. It's recommended to fast and take advantage of the subtle influences of the eclipse time.
The solar eclipse takes place in two weeks on March 29th during the new moon (amavasya). These two weeks are within the "eclipse cycle" and is considered an unstable time period for beginning major projects, signing documents etc.
Whatever position in the horoscope that an eclipse takes place represents an area of potential change, and transformation. This is especially true if it's close in degrees to key positions like the ascendant, Sun or Moon, or another planet. To learn about solar eclipses see the article: What is a Solar Eclipse.