Sep 25 - Lunar and solar eclipses Flashcards
2 types of eclipses:
- Lunar eclipse
- Solar eclipse
Lunar eclipse:
Occurs when Earth comes directly between the sun and moon, so that earth’s shadow falls on the moon
Full moon phase
Because earth is much larger than the moon, Earth’s shadow can cover the entire moon during a lunar eclipse
Thus, a lunar eclipse can be seen by anyone on the night side of earth when it occurs
REASON TO WHY WE SEE LUNAR ECLIPSES MORE OFTEN THAN SOLAR ECLIPSES
Solar Eclipse:
Occurs when the moon comes directly between the sun and earth, so that the moon’s shadow falls on the earth
New moon phase
The moon’s shadow can cover only a small portion of the Earth at any one moment, so you must be located within the relatively narrow pathway through which the shadow moves to the a solar eclipse
Shadow consists of two distinct regions:
Central full shadow/Umbra: sunlight is fully blocked
Partial Shadow/Penumbra: light from only part of the sun is blocked
How does a lunar eclipse occur?
Begins at the moment when the Moon’s orbit first carries it into Earth’s partial shadow
After, we see one of three types of lunar eclipses:
- Total
- Partial
- Penumbral
Total Lunar Eclipse:
if the sun, earth, and moon are nearly perfectly aligned, the moon passes through earth’s full shadow (umbra)
Earth’s full shadow crosses the face of the moon, proving that our world is round
Totality: begins when the Moon is entirely engulfed in the full shadow and typically lasts about an hour, after which we see the shadow gradually move off the Moon
Moon becomes red during this time
– Observers from the moon would see Earth’s night side surrounded by the reddish glow of all the sunrises and sunsets occurring on Earth at that moment, which means that this reddish light illuminates the Moon during totality
Partial Lunar Eclipse:
when alignment is somewhat less perfect, only part of the moon passes only through earth’s partial shadow (penumbra)
Penumbral Lunar Eclipse:
If the moon passes only through Earth’s partial shadow (penumbra)
Most common, but least visually appealing
3 types of solar eclipses:
- Total
- Annular
- Partial
Total Solar Eclipse
when the moon is in a part of its orbit where it is relatively close to earth, the moons full shadow can cover a small area of Earth’s surface
Moon appears to take bites of the sun; sky darkens, temps fall
Annular Eclipse
when the moon is in a part of its orbit that puts it farther from earth, the full shadow may not reach earth’s surface; a ring of sunlight surrounding the moon in the small region of earth directly behind the full shadow
Partial Solar Eclipse
the region of totality or annularity will be surrounded by a much larger region that falls within the moon’s partial shadow; only part of the sun is blocked from view
How do solar eclipses happen?
Both earth’s rotation + moon’s orbital motion causes the moon’s shadow to race across the face of earth at a typical speed of about 1700km per hour
Result: the full shadow traces a narrow path across Earth, and totality never lasts more than a few minutes in any particular place.
Why don’t we have eclipses every month?
The moon’s orbit is slightly inclined by about 5 deg to the ecliptic place
Moon spends most of its time either above or below the “pond surface”/ecliptic
Crosses through this surface only twice during each orbit - once coming out, once going back in
2 POINTS AKA: NODES
How do nodes work and affect eclipses?
Nodes are aligned the same way throughout the year, which means they lie along a nearly straight line with the sun and each about twice each year
Eclipses can only occur during these periods, called “eclipse seasons”, which last around 5 weeks on average
the phase of the Moon is full (for a lunar eclipse) or new (for a solar eclipse) and
the new or full moon occurs when the Moon is very close to a node, which means it is during an eclipse season.
