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Total Solar Eclipse; Terms you need to know courtesy of NASA

Photo: Ken Lund / CC BY-SA 2.0 via MGN

The 2017 Total Solar Eclipse is now within 10 days. Our team will be teaching you more about this celestial event in the coming days so you are prepared for it whether you are staying here in the DC area or traveling to the path of totality. First and foremost, you should learn some of the terms. Some of them are a little tricky which is why NASA has developed a list online to try and help explain them. We have included the terms, courtesy of NASA, below that we think are important for the public to grasp ahead of the event.

All info courtesy of NASA:

  • "Total Eclipse - A solar eclipse in which the Moon's umbral shadow traverses Earth (Moon is close enough to Earth to completely cover the Sun). During the maximum phase of a total eclipse, the Sun's disk is completely blocked Moon. The Sun's faint corona is then safely revealed to the naked eye." What is an eclipse? Find out more here!
  • "Partial Eclipse - A solar eclipse in which the Moon's penumbral shadow traverses Earth (umbral and antumbral shadows completely miss Earth). During a partial eclipse, the Moon appears to block part (but not all) of the Sun's disk. From the prospective of an individual observer, a partial eclipse is one in which the observer is within the penumbral shadow but outside the path of the umbral or antumbral shadows." Find out what you'll see in your area here
  • "Totality - The maximum phase of a total eclipse during which the Moon's disk completely covers the Sun. Totality is the period between second and third contact during a total eclipse. It can last from a fraction of a second to a maximum of 7 minutes 32 seconds." Path of Totality here
  • "Umbra - The umbra is the darkest part of the Moon's shadow. From within the umbra, the Sun is completely blocked by the Moon as in the case of a total eclipse. This contrasts with the penumbra, where the Sun is only partially blocked resulting in a partial eclipse." Diagram of an Umbra vs Penumbra
  • "Penumbra - The penumbra is the weak or pale part of the Moon's shadow. From within the penumbra, the Sun is only partially blocked by the Moon as in the case of a partial eclipse. This contrasts with the umbra, where the Sun is completely blocked resulting in a total eclipse." Learn more about the penumbra here
  • "Third Contact - The instant when the total or annular phase of an eclipse ends."
  • "Central Line - During a central solar eclipse, the central axis of the Moon’s shadow cone traverses Earth's surface. The track produced by the shadow axis is called the central line of the eclipse. The duration of a total or annular eclipse is longest on the central line (neglecting Earth's curvature and effects introduced by the direction of the shadow with respect to the Equator) and drops to 0 as the observer moves to the path limits." Interactive map
  • "Eclipse Magnitude - Eclipse magnitude is the fraction of the Sun’s diameter occulted by the Moon. It is strictly a ratio of diameters and should not be confused with eclipse obscuration, which is a measure of the Sun’s surface area occulted by the Moon. Eclipse magnitude may be expressed as either a percentage or a decimal fraction (e.g., 50% or 0.50). By convention, its value is given at the instant of greatest eclipse."
  • "Eclipse Obscuration - Eclipse obscuration is the fraction of the Sun’s area occulted by the Moon. It should not be confused with eclipse magnitude, which is the fraction of the Sun’s diameter occulted by the Moon. Eclipse obscuration may be expressed as either a percentage or a decimal fraction (e.g., 50% or 0.50)." More on magnitude vs. obscuration
  • "Eye Safety - The only time that the Sun can be viewed safely with the naked eye is during a total eclipse, when the Moon completely covers the disk of the Sun. It is never safe to look at a partial or annular eclipse, or the partial phases of a total solar eclipse, without the proper equipment and techniques. Even when 99% of the Sun's surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause permanent retinal damage, especially when viewed through binoculars or other optical aids." View more very important safety tips!

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