Solar and Lunar Eclipses

Editor's Notice: The content found on this page has been found outdated and we will be modifying this page soon. We recommend for facts about solar and lunar eclipses you check out the following pages provided by the U.S. National Aeronautics and Space Administration (NASA):

• Solar Eclipse
• Lunar Phase and Lunar Eclipse

A solar eclipse occurs when the Moon passes between the Sun and Earth, casting the Moon's shadow on Earth.  A solar eclipse can only happen during a New Moon.  The Moon's orbit is titled 5 degrees to Earth's orbit around the Sun.  Therefore a solar eclipse is a relatively rare phenomena and a Total or Annular eclipse even more rare, with the Hybrid eclipse the rarest of all.  

To understand the difference between a Total and Annular eclipse of the Sun, it must be understood that the Moon has an elliptical orbit around Earth.  In fact, the Moon's distance from Earth varies from a minimum of 221,000 to a maximum of 252,000 miles.  Therefore the Moon's apparent size in our sky will vary by 13%.  When the Moon's orbit is toward its minimum distance from Earth, the Moon will appear visually as a larger disk than the Sun.  If an eclipse occurs during this time, it will be a Total solar eclipse because the Moon has totally obscured the Sun's disk, producing the beautiful solar corona ejecting outward from the Sun.  One important element to remember though is that the Moon's shadow will obviously become narrower as it is cast from the Moon to Earth (in a shape of a cone with the wide end being at the Moon and the narrow end on Earth).  Therefore the path of totality on Earth is narrow.  It is also very short-lived as the Moon is moving quickly away from its perfect location of being situated between the Sun and Earth. 

An Annular solar eclipse is different than Totality in that it occurs when the Moon is closer to its maximum distance from Earth in its orbit.  If an eclipse happens during this situation, the Moon will appear visually smaller than the Sun and its shadow cast will not be long enough to reach Earth.  What reaches Earth is the antumbral or "negative" shadow.  If you are within the antumbral shadow, you will see a solar eclipse where a thin ring or annulus of bright sunlight surrounds the Moon.  Therefore Annular solar eclipses are still spectacular in that they are almost Total, but the solar corona is not seen due to the brightness of the annulus.  Like a Total eclipse, the Annular solar eclipse will have a narrow path on Earth with short duration, most often less than 10 minutes. 

A Hybrid eclipse is especially rare in that an Annular eclipse can change to a Total eclipse, or vice versa, along the eclipse path.  Due to Earth's curvature, Earth may move through the Antumbral shadow (Annular eclipse) and Umbral shadow (Total eclipse) along different points of the eclipse path.   

DO NOT observe a solar eclipse with the naked eye.  Serious eye damage can result.  Use approved solar filters or cut a pin hole in a shoe box and watch the Sun's light cast through the pin hole onto a smooth surface such as cardboard.  The only portion of a solar eclipse which is safe to view without filters is the brief time during totality.  Otherwise all partial solar eclipses need approved filters.  For approved filters, look for a certification of International Standard ISO 12312-2.  The next solar eclipse which will be visible in the United States will occur on April 8, 2024.

DATES OF UPCOMING TOTAL AND ANNULAR SOLAR ECLIPSES AND LOCATIONS OF BEST VIEWING

A Lunar eclipse occurs when the Sun casts Earth's shadow onto the Moon.  For this to happen, the Earth must be physically between the Sun and Moon with all three bodies lying on the same plane of orbit.  A lunar eclipse can only occur during a Full Moon and when the Moon passes through all or a portion of Earth's shadow.  

The outer portion of the shadow cast from Earth is known as the penumbral shadow, which is an area where Earth obstructs only a part of the Sun's light from reaching the Moon.  The umbral shadow is the "inner" shadow, which is the area where Earth blocks all direct sunlight from reaching the Moon.  A penumbral lunar eclipse is subtle and very difficult to observe.  A partial lunar eclipse is when a portion of the Moon passes through the Earth's umbral shadow.  Finally, a total lunar eclipse is when the entire Moon passes into the Earth's umbral shadow.  During a total lunar eclipse, the sequence of eclipses are penumbral, partial, total, partial and back to penumbral.  

Unlike solar eclipses, a total lunar eclipse lasts a few hours, with totality itself usually averaging anywhere from about 30 minutes to over an hour.  This is due to the large relative size of Earth over the Moon (the Moon's diameter is only about 2150 miles), therefore casting a large umbral shadow on the Moon.  In addition, lunar eclipses are more frequent than their solar counterparts.  There are zero to three lunar eclipses per year (although possibly not all at the same location on Earth) where the Moon passes through at least a portion of the Earth's umbral shadow (producing a partial to total eclipse).  As stated above in the solar eclipse explanation, the Moon's orbit is tilted 5 degrees from Earth's orbit.  For an eclipse to occur, the Moon and Earth have to be on the same orbital plane with the Sun, so the Earth's shadow can be cast onto the Moon from the Sun.  This is why lunar eclipses only occur on average one or two times a year instead of every month.  

Even though the Moon is immersed in the Earth's umbral shadow, indirect sunlight will still reach the Moon thus illuminating it slightly.  This is because indirect sunlight reaches the Moon and also the Earth's atmosphere will bend a very small portion of sunlight onto the Moon's surface.  Many times during lunar totality, the color of the Moon will take on a dark red hue or brown/orange color.  As sunlight passes through Earth's atmosphere, the blue-light is scattered out.  The amount of illumination of the Moon will vary depending on how much dust is in the Earth's atmosphere.  The more dust present in the atmosphere, the less illuminated the Moon will be. 

Lunar eclipses are safe to be viewed by the naked eye, through binoculars or a telescope.  Below is a table which shows partial and total lunar eclipses visible in the United States.

Eclipse predictions courtesy of Fred Espenak, NASA/Goddard Space Flight Center, eclipse.gsfc.nasa.gov