Thread: Why does the Sun and Moon appear the same size during Solar eclipse? and why does Earths shadow happen to fit the Moon's surface exactly perfectly during Lunar eclipse?

Hey!

I just registered hoping somebody can help me understand why the moon happens to be such a size and at such a distance that it appears to be the same size as the Sunduring a Solar eclipse. Is it a coincidence of some kind? or are there forces/factors at play?

I find it difficult to word the question properly...

To make this seem even more mysterious and strange in my mind is the fact that the Earth's shadow happens to be the same size as the moon during a lunar eclipse... this mystery/phenomena/coincidence/syncranisation has been puzzling me for a little while now. Though im not the brightest, so hopefully some of you science dudes can explain it to me?

Many thanks

Originally Posted by question for you

I just registered hoping somebody can help me understand why the moon happens to be such a size and at such a distance that it appears to be the same size as the Sunduring a Solar eclipse. Is it a coincidence of some kind? or are there forces/factors at play?

It is just a coincidence. As the moon is slowly moving away from the Earth, one day it will no longer be true.

To make this seem even more mysterious and strange in my mind is the fact that the Earth's shadow happens to be the same size as the moon during a lunar eclipse...

I'm pretty sure that is not the case. If it were then the Earth would appear to be the same size from the moon as the moon does from earth - and that can't be true. Remember, you can't see the whole shadow of the earth (even if a lunar eclipse is total) so the shadow could be (is) much bigger than the moon and you couldn't easily tell.

Hmm isnt the thing about the moon moving away from us just a theory? Its on an eliptical orbit so it must be hard to measure...?

It's a pretty crazy coincidence if you ask me.

About the Lunar eclipse... Maybe your right, im not sure where i got the idea that earths shadow is same size as moon... What is a Lunar eclipse anyway? isnt it just a 'new' moon? and we have them every month!

Thanks for your reply strange

P.S... Earths shadow can't be much bigger than the Moon as it looks fairly curved during cresent Moons...

Originally Posted by question for you

Hey!

I just registered hoping somebody can help me understand why the moon happens to be such a size and at such a distance that it appears to be the same size as the Sunduring a Solar eclipse. Is it a coincidence of some kind? or are there forces/factors at play?

It is just a coincidence of the time. In fact, sometimes the moon is smaller than the sun; we then get an annular solar eclipse like the last one.

To make this seem even more mysterious and strange in my mind is the fact that the Earth's shadow happens to be the same size as the moon during a lunar eclipse... this mystery/phenomena/coincidence/syncranisation has been puzzling me for a little while now. Though im not the brightest, so hopefully some of you science dudes can explain it to me?

Many thanks

In fact, the earth's shadow is much larger than the moon. I'm having trouble posting images, so will follow up with another post demonstrating these points.

Annular Solar Eclipse

annulareclipse.jpg

Earth's shadow during lunar eclipse:

lunareclipse.jpg

Ok how do you guys qoute me like that? I cant find the quotation tool...

The moon appears smaller than the sun...? when its at the furthest piont on its eliptic? and does it appear bigger when its at it nearest piont on its eliptic? Whats all that about anual solar eclipse like 'the last one'?

I wonder how long the moon has appeared to be that size relative to the sun?

I can understand the earths shadow being larger than moon... why does lunar eclipse sometimes look red? and what is a lunar eclipse if it's not a new moon?

Thanks for your post wayne

The moon is slowly moving away from the earth due to tidal interactions between the earth and moon. A billion years in the past, the moon was closer and would cover the sun completely any time the two aligned. In another billion years it will be too far away all the time, and will never completly cover the sun.

Right now, we're at the sweet spot, so that when the moon is closer to the earth (near perigee) in it's highly elliptical orbit at the time of the alignment, it is large enough to cover the sun. When it is further away (near apogee) it is smaller than the sun. The May 20, 2012 eclipse was one of those times, so produced an annular eclipse like the image I posted.

The moon looks red during a lunar eclipse, because while the sun is behind the earth (from the moon's point of view) all around the edge of the dark earth are all the sunrises and sunsets of the earth, so the red light is what faintly lights up the moon. Ever notice how sunsets are often red? Well imagine all the sunsets and sunrises encircling the earth.

Originally Posted by question for you

Hmm isnt the thing about the moon moving away from us just a theory?

What do you mean "just" a theory? If it is a theory, then it means it is pretty well established. A theory is the closest science comes to "true". It is also confirmed by experiment: the Lunar Laser Ranging experiment can measure the distance an accuracy of a few centimeters. Apache Point Observatory Lunar Laser-ranging Operation - Wikipedia, the free encyclopedia

Yes the moon moving away is just a theory. The Theory of Gravity. It's not just a theory, it's the law!

A new moon occurs once for every revolution of the moon around the Earth, when the moon is between the sun and the Earth. As a consequence the farside of the moon is lit, but no sunlight reaches the side facing the Earth. A lunar eclipse occurs when the moon is on the far side of the Earth, further away from the sun and is caused by the Earth's shadow.

I dont beleive what you say about a million or billion yrs in past or future... thats getting a bit big for ya boots if you ask me.

Is there any proof that the moon is moving further away due to tidal interactions?

The sunrises and sunsets are not always red... are lunar eclipses always red?

And any insight on the difference between 'New moon', which is when the earths shadow hides the moon once per cycle at oposite piont to a full moon... (I think), and a lunar eclipse?

Originally Posted by John Galt

A new moon occurs once for every revolution of the moon around the Earth, when the moon is between the sun and the Earth. As a consequence the farside of the moon is lit, but no sunlight reaches the side facing the Earth. A lunar eclipse occurs when the moon is on the far side of the Earth, further away from the sun and is caused by the Earth's shadow.

Quite right! I had a mental block then. Thank you.

Originally Posted by MeteorWayne

Yes the moon moving away is just a theory. The Theory of Gravity. It's not just a theory, it's the law!

I would have to say theory is not the closest thing to truth... fact is.

Originally Posted by question for you

Originally Posted by MeteorWayne

Yes the moon moving away is just a theory. The Theory of Gravity. It's not just a theory, it's the law!

I would have to say theory is not the closest thing to truth... fact is.

..............That was meant to be a reply for another comment, sorry wayne.... gravity attracts so why would moon be slipping away?

Originally Posted by question for you

I dont beleive what you say about a million or billion yrs in past or future... thats getting a bit big for ya boots if you ask me.

The Universe doesn't really care if you believe me or not. Facts are facts.

Is there any proof that the moon is moving further away due to tidal interactions?

Yes, see Strange's post.

The sunrises and sunsets are not always red... are lunar eclipses always red?

I didn't think I had to explain that, since you phrased the question as "why does lunar eclipse sometimes look red?
The exact color varies for each lunar eclipse depending on the cloudiness and dust load of all the sunrises and sunsets at that particular time.

Originally Posted by Strange

Originally Posted by question for you

Hmm isnt the thing about the moon moving away from us just a theory?

What do you mean "just" a theory? If it is a theory, then it means it is pretty well established. A theory is the closest science comes to "true". It is also confirmed by experiment: the Lunar Laser Ranging experiment can measure the distance an accuracy of a few centimeters. Apache Point Observatory Lunar Laser-ranging Operation - Wikipedia, the free encyclopedia

I say 'just a theory' becuase a theory is just that, its an educated or uneducated guess.... Fact is the closest thing science (knowledge of truth) has to the truth

ANd the math that explains it has been well understood for a century or more.

Originally Posted by MeteorWayne

Originally Posted by question for you

I dont beleive what you say about a million or billion yrs in past or future... thats getting a bit big for ya boots if you ask me.

The Universe doesn't really care if you believe me or not. Facts are facts.
Now theres a statement! You didnt show me any facts, and i didnt say anything about the universe 'caring'

Is there any proof that the moon is moving further away due to tidal interactions?

Yes, see Strange's post.
I did, thank you

The sunrises and sunsets are not always red... are lunar eclipses always red?

I didn't think I had to explain that, since you phrased the question as "why does lunar eclipse sometimes look red?
The exact color varies for each lunar eclipse depending on the cloudiness and dust load of all the sunrises and sunsets at that particular time.

Ofcourse

Originally Posted by question for you

I say 'just a theory' becuase a theory is just that, its an educated or uneducated guess....

Nonsense. A theory is a well tested (i.e. "proved" in the original sense of the word) explanation with solid theoretical (i.e. mathematical) and evidentiary support.

Science is not based on guesswork.

In the case of the recession of the moon we have a solid theoretical explanation based on Newton's laws, as modified by Einstein's work, and experimental evidence. That is as close to "fact" as science gets.

The definition of the term "theory" in science is far more rigorous than the idea it that is "just a theory" as we commonly understand the term. A scientific theory has to provide us with predictions that we can test which might invalidate the theory, for instance.

Scientific theory - Wikipedia, the free encyclopedia

Originally Posted by Strange

Originally Posted by question for you

I say 'just a theory' becuase a theory is just that, its an educated or uneducated guess....

Nonsense. A theory is a well tested (i.e. "proved" in the original sense of the word) explanation with solid theoretical (i.e. mathematical) and evidentiary support.

Science is not based on guesswork.

In the case of the recession of the moon we have a solid theoretical explanation based on Newton's laws, as modified by Einstein's work, and experimental evidence. That is as close to "fact" as science gets.

You seem to have spent a lot of time learning stuff... yet you still dont know the difference between a theory and a fact.... which is ellementary and should be understood early in the reasearch process!

Originally Posted by SpeedFreek

The definition of the term "theory" in science is far more rigorous than the idea it that is "just a theory" as we commonly understand the term. A scientific theory has to provide us with predictions that we can test which might invalidate the theory, for instance.

Scientific theory - Wikipedia, the free encyclopedia

I checked the link. So scientific theory is different from theory is it? ok. But the page still confirms that a theory is a explanation which evolves as evidence grows etc. the comment about 'Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge' doesnt make sense to me. A fact such as 'fire burns' is more reliable 'scientific knowledge' than an explanation that evolves until the whole truth is learnt (theory). Some theories are far more accurate than others as they have evolved more and or have more evidence to help them develop... whereas all facts are fixed truths and therefor the most reliable form of scientific knowledge.

you guys know wiki isnt a robust source right?

Thanks for your input speed

Originally Posted by question for you

A fact such as 'fire burns' is more reliable 'scientific knowledge' than an explanation that evolves until the whole truth is learnt (theory).

But the "fact" by itself is so vague as to be useless. How do you define "fire" and how do you quantify or explain it? What does "burn" mean? How do you quantify or explain that? Does the sun "burn" in the same way as a candle or an acid? Your "fact" might be one input to the formation of a theory which can begin to answer some of these questions. That is what science is all about: getting beyond obvious "facts" towards an explanation.

I couldnt think of a good 'fact'... How about electric flows through conductors... thats not a theory is it? thats an observable fact.

Anyway, I think the general message is that there is no explanation about why the moon appears the same size as the sun, its just a weird coincidence, a random syncrinisation, order out of chaos or something...

Originally Posted by question for you

I couldnt think of a good 'fact'... How about electric flows through conductors... thats not a theory is it? thats an observable fact.

Right. But by itself it doesn't tell us anything. Until someone like Faraday did a huge number of experiments with different currents and looked at the magnetic fields generated - and the currents generated by changing magnetic fields. This was formalised as a theory by Maxwell who produced a mathematical description. This, importantly, was useful as it forms the basis of much electrical and electronic engineering. It is also the basis that Einstein and others used to develop the theory of relativity.

See how much more useful a theory is than a simple "fact"?

Anyway, I think the general message is that there is no explanation about why the moon appears the same size as the sun, its just a weird coincidence, a random syncrinisation

Exactly.

Thank you all for your comments

Originally Posted by question for you

you guys know wiki isnt a robust source right?

Of course. Wiki is often, however, the easiest place to find a robust source - you can see a big list of references at the bottom of the article. National Academy of Sciences, etc etc.



Oh, and "fire burns" is a law. The first step is to understand the difference between a law and a theory, in science.

Originally Posted by SpeedFreek

Originally Posted by question for you

you guys know wiki isnt a robust source right?

Of course. Wiki is often, however, the easiest place to find a robust source - you can see a big list of references at the bottom of the article. National Academy of Sciences, etc etc.



Oh, and "fire burns" is a law. The first step is to understand the difference between a law and a theory, in science.

Forgive me for not checking the refference list, your right.

So in science speak, a law is a fact. A theory is neither. But we'r agreed a law is the most reliable form of scienticfic knowledge?

Originally Posted by question for you

So in science speak, a law is a fact. A theory is neither. But we'r agreed a law is the most reliable form of scienticfic knowledge?

I don't think the term "law" is used much any more. If anything it just denotes a very well established theory. But, for example, Newton's Law of Universal Gravitation has been replaced by Einstein's Theory of General Relativity (which is therefore the more accurate/reliable explanation).

It is only in mathematics that we can have proof.

I need to learn more about maths... I struggle with the language. I'd like to understand maths, where to start?

Of course the term "law" is used.

We still use the laws of thermodynamics, don't we?

Originally Posted by question for you

I couldnt think of a good 'fact'... How about electric flows through conductors... thats not a theory is it? thats an observable fact.

Anyway, I think the general message is that there is no explanation about why the moon appears the same size as the sun, its just a weird coincidence, a random syncrinisation, order out of chaos or something...

I thought that was made clear in post #2 and post #5.

The earth's orbit around the sun causes a very small change in size of the sun (~3%) because the orbit is close to circular (eccentricity currently 0.0167). The moons orbit around the earth is far more eccentric (e=0.569)and causes a much greater size variation (~13.5%).

See images in next post

Lunar variation:

Attachment 867

Solar Variation:

Attachment 868


Sun/Moon at perigee, you can clearly see how much larger than the sun the moon is:

Attachment 869


May Annular Eclipse, where obviously the moon is smaller than the sun:

Attachment 870

Sun/Moon at perigee, you can clearly see how much larger than the sun the moon is:

Attachment 869


May Annular Eclipse, where obviously the moon is smaller than the sun:

Attachment 870

Hmmm, not sure what the image problem is...

When I hear ‘just a theory’, that sounds like something many a creationist might say in an attempt to demean evolution. Maybe I’m reading too much between the lines on where this post is aiming towards

But I like the question. I remember the last total solar eclipse back in 1999. Heralded as the last total solar eclipse of the century. Unfortunately for me it was only a partial eclipse due to my location but it was still a surreal moment. Many damaged their eyes that day.

Originally Posted by MeteorWayne

Hmmm, not sure what the image problem is...

1002011_00.JPG

Me neither.

Originally Posted by MeteorWayne

Hmmm, not sure what the image problem is...

I looked in the attachment manager in the administrator control panel and it shows two images for you since July 16, lunareclipse.jpg and annulareclipse.jpg. It would appear the rest were not successfully uploaded.

Yeah i think you may be reading to much into that pinneapple, maybe the whole evolutionist vs creationist debate has been ingrained into your psyche so deeply that you see it everywhere? im just teasing. I don't think of myself as a creationist or an evolutionist but then again, i beleive evolution happens because things do adapt to enviroments, though the changing or evolution of one species into another has never been witnessed as far as I know, just adaptation of some species as pointed out by Darwin who I think said natural selection was the mechanism behind evolution. Also though, I think things are created in a sense, thats why we'r all called creatures isn't it? beucause somehow everything is created into existence... even the sofa i sit on is a creation isn't it? so maybe im a creationist and an evolutionist. you got a problem?

I remember the '99 eclipse too... surreal is a good word! it's surreal indeed, that's why i've been wondering about the phenomena. I wondered if science could explain why? How? but it seems there is no explanation as yet (on google). It's beyond comprehension, a total mystery. Whoooooo hooo!
Thanks for posting

Originally Posted by pineapples

When I hear ‘just a theory’, that sounds like something many a creationist might say in an attempt to demean evolution. Maybe I’m reading too much between the lines on where this post is aiming towards

But I like the question. I remember the last total solar eclipse back in 1999. Heralded as the last total solar eclipse of the century. Unfortunately for me it was only a partial eclipse due to my location but it was still a surreal moment. Many damaged their eyes that day.