difference between umbra and penumbra
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difference between umbra and penumbra
Penumbra is a derived term of umbra.
In context|astronomy|lang=en terms the difference between penumbra and umbra
is that penumbra is (astronomy) a region around the edge of a sunspot, darker than the sun’s surface but lighter than the middle of the sunspot while umbra is (astronomy) the central region of a sunspot.
As nouns the difference between penumbra and umbra
is that penumbra is a partially shaded area around the edges of a shadow, especially an eclipse while umbra is a shadow.
The main difference between penumbra and umbra is that they are different parts of a shadow having different densities of darkness. Penumbra is the shadow that forms in the perimeters of the umbra. It is light in color density. Umbra is the shadow formed in the center. It is the darkest having a high density of black color.
Penumbra is the light part of a shadow. It is formed in the perimeter of the umbra. Penumbra is the term given to the shadow formed by the heavenly objects. Penumbra is derived from the Latin word paene, meaning almost or nearly. It is normally formed and observed during the eclipse. The penumbra
is observed during the partial or half eclipse, as the moon is partially covered by the sun, and the penumbra portion is observed.
Umbra is the darkest portion of the shadow formed. It is mostly formed in the center of the portion. It is considered a part of the penumbra. its also formed parallel with penumbra. During the eclipse, the umbra starts to become smaller. During the eclipse, an observer within the area of the umbra always experiences a full eclipse. And the full lunar eclipse, the moon is completely covered with the umbra, and the penumbra part becomes invisible.
Comparison Table Between Penumbra and Umbra
| Parameters of Comparison | Penumbra | Umbra |
| First used in | 1604 | 1950 |
| Meaning | Nearly a shadow or almost a shadow | Shadow |
| Color of shadow | Lighter in color than the umbra | Darkest portion of the shadow |
| Position | On the perimeters of the shadow area | At the center of the whole shadow portion |
| During eclipse | Becomes larger | Becomes smaller |
What Is the Umbra?
The umbra is the dark center portion of a shadow. The Moon‘s umbra causes total solar eclipses, and the Earth’s umbra is involved in total and partial lunar eclipses.
Like any other opaque objects illuminated by a light source, the Moon and the Earth cast shadows into space as they block the sunlight that hits them. Each shadow has 3 different areas: the umbra, the penumbra, and the antumbra.
Umbra Definition
The umbra is a shadow‘s dark core. Imagine a light source and an object casting a shadow. If you are standing within the umbra, you will not be able to see any part of the light source as the object blocks all direct light rays.
The other 2 areas are:
- Penumbra – the lighter outer part of the shadow.
- Antumbra – the lighter part of the shadow that begins where the umbra tapers to a point.
How Large Is the Moon’s Umbra?
The size of the area on the Earth’s surface covered by the Moon’s umbra during a total solar eclipse depends, amongst other things, on the Moon’s current distance from Earth. The smaller the distance, the larger the umbra.
If the Moon is at its closest to Earth (its perigee) during the eclipse, the Moon appears larger in the sky. In that case, the umbra’s path across the Earth’s surface typically has a width of roughly 150 km (90 mi) at the Earth’s equator. At higher latitudes, the Sun’s rays hit the Earth’s surface at a shallower angle, so the umbra’s size grows accordingly. During some total solar eclipses, the umbra’s path width reaches over 1000 km (600 mi) at the poles.
If the eclipse occurs when the Moon’s distance is greater, the tip of the Moon’s cone-shaped umbra (see illustration) may only just reach the Earth’s surface during parts of the eclipse, meaning that its diameter is close to zero. The total phase of the solar eclipse then lasts only a short moment. For example, the total solar eclipse on December 6, 2067 will last only 8 seconds at its maximum point, with partial phases before and after totality. This eclipse will be a hybrid solar eclipse.
If the Moon is close to its apogee, its farthest from Earth, during the eclipse, the umbra does not reach the Earth’s surface at all, and it is replaced by the antumbra, producing an annular solar eclipse.
What is Penumbra?
“Pen” is derived from the Latin word “pendere” which means “to hang”. Another Latin origin is “paene” which means “almost”. As “umbra” translates to “shadow”, the penumbra is the lighter part which “hangs on the shadow” or that which is “almost a shadow”. “Penumbra” was coined by a German astronomer and
mathematician, Johannes Kepler in 1604. He utilized the word to aptly describe the blurry shadow surrounding an eclipse. It is not a true shadow as it is only a gradient of the umbra. Regarding eclipses, it is the region of partial illumination. It is also defined as a sunspots’ gray area which surrounds the dark center.
Though penumbra is mainly associated with shadows and eclipses, it also has the following definitions:
- A surrounding area or region
- A guaranteed bill of rights by implication
- Something that obscures or covers
- Indefinite or marginal
What’s a penumbral eclipse of the moon?
An eclipse of the moon can only happen at full moon, when the sun, Earth and moon line up in space, with Earth in the middle. At such times, Earth’s shadow falls on the moon, creating a lunar eclipse. Lunar eclipses happen a minimum of two times to a maximum of five times a year. There are three kinds of lunar eclipses: total, partial and penumbral.
In a total eclipse of the moon, the inner part of Earth’s shadow, called the umbra, falls on the moon’s face. At mid-eclipse, the entire moon is in shadow, which may appear blood red.
In a partial lunar eclipse, the umbra takes a bite out of only a fraction of the moon. The dark bite grows larger, and then recedes, never reaching the total phase.
In a penumbral lunar eclipse, only the more diffuse outer shadow of Earth – the penumbra – falls on the moon’s face. This third kind of lunar eclipse is much more subtle, and much more difficult to observe, than either a total or partial eclipse of the moon. There is never a dark bite taken out of the moon, as in a partial eclipse. The eclipse never progresses to reach the dramatic minutes of totality. At best, at mid-eclipse, very observant people will notice a dark shading on the moon’s face. Others will look and notice nothing at all.
According to eclipse expert Fred Espenak, about 35% of all eclipses are penumbral. And the final 35% go all the way to becoming total eclipses of the moon, a beautiful natural event.
Forming an Umbra and Penumbra
You can experiment with umbras and penumbras at home. Find a blank wall, and position a light source 6 to 10 ten feet away from it. Turn the light on, and stand between the light source and the wall. Take note of your shadow on the wall. As you move closer to the wall, the darkest part of the shadow — the umbra — darkens and the partial shadow — the umbra — begins to fade more fully into the umbra. As you move away from the wall, your shadow grows and the umbra gradually gives way to the penumbra.
Is the umbra or penumbra hotter?
The penumbra is the outer, relatively light region of a sun spot. It is shaped like an annulus (a ring) surrounding the darker, cooler umbra.
What are the 3 types of shadows?
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object.
Summary of Penumbra vs Umbra
- Penumbra and umbra are terms which physicists use in describing the volume of shadows.
- “Penumbra” was coined by Kepler, a German astronomer and mathematician.
- “Umbra” was figuratively used in the 1590s to denote “ghost” or “phantom”.
- “Umbra” means “shadow” while “penumbra” means “to hang on the shadow”.
- The umbra is darker than the penumbra.
- The penumbra surrounds the umbra.
- A penumbral lunar eclipse is usually difficult to notice.
- During a solar eclipse, you would be in the umbra region if there would be darkness while you would be in the penumbra if you would see a “partial” sun.
- There are more searches for “penumbra” as compared to “umbra” according to the Ngram Viewer.
- Umbra was first used in the 1950s while penumbra was coined in 1604.
- Unlike “umbra”, “penumbra” is also a terminology used in painting and in the US constitution.
- Unlike “penumbra”, “umbra” has less variations regarding its meanings and usage.
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