Fog and clouds so with the lunar eclipse it was DARK outside.

We had several deer who think they are sneaking into our apples ........if they only knew it was me picking them and chopping them up so the babies can eat too.

So after some years I'm back in FNQ at my usual holiday haunt of Port Douglas and there is going to be a total lunar eclipse next week ! Well it's not so usual as we now have the constant challenge of COVID, but it's been my first opportunity to travel very far for several years. Now according to this page the eclipse will be potentially viewable at my location for almost all of it's phases at around 7pm in the evening of the 8th. That would be seen as rising in the east over the beautiful Coral Sea while the Sun sets in the west. Here's hoping for clear skies and thus some good snaps of the 'blood' moon.

I'll post more later.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

So after some years I'm back in FNQ at my usual holiday haunt of Port Douglas and there is going to be a total lunar eclipse next week ! Well it's not so usual as we now have the constant challenge of COVID, but it's been my first opportunity to travel very far for several years. Now according to this page the eclipse will be potentially viewable at my location for almost all of it's phases at around 7pm in the evening of the 8th. That would be seen as rising in the east over the beautiful Coral Sea while the Sun sets in the west. Here's hoping for clear skies and thus some good snaps of the 'blood' moon.

I'll post more later.

Cheers, Mike.

That would be really cool if things worked out so you can see the whole thing!!

Thanks for the encouragements. As I've left my digital SLR at home I'll look into hiring a camera for the day. ;-)

The Geometry of Eclipses 1 : Let's have a think about why it is that these eclipse events occur at all. For starters let us think of a stripped down version of the solar system. That is, no other planets or moons, including our moon. Just the Sun and the Earth. To an outstanding degree of accuracy we can use Newton's Law of Gravity ( plus F = ma and the equality of action/reaction ) to describe it. For a given pair of objects the force is separately proportional to either body's mass and inversely proportional to the distance between them. There is a comparatively small constant of proportionality to scale the law to our measurements in some system of physical units^{*}. For the moment we may also ignore the Earth's or Sun's rotation about their own axes.

Now the Earth and the Sun orbit - around each other - in a shape called an ellipse around their common centre of mass^{**}. An ellipse is a type of 'conic section' which is a possible type of orbit under Newton's laws. It occurs when there is insufficient energy for either body to escape from the other. A circle is an ellipse with no 'eccentricity' - the number that determines the degree to which an ellipse deviates from a circle. That is, a perfect circle has an eccentricity of zero. Other possible solutions are a parabola ( just enough energy to escape, with zero velocity at infinite separation ) and a hyperbola ( enough energy to escape to infinity with non zero velocity ). So a parabola is the 'edge case' between bound and unbound systems. Having said all of that^{***}, let the orbits be circular which they nearly are anyway. Note that all these conic sections are planar objects.

Now, for each moment in time, draw a line starting at the centre of the Sun, going through the centre of the Earth and outwards to infinity. As time goes on the infinitely far away end of that line - or the succession of such lines over time - traces out a path through the pattern of distant stars. This path is called the ecliptic, and please note the highlighted letter 'c' ie. not elliptic. Here there is some slight confusion : ecliptic can also be used as an abbreviation to 'the plane of the ecliptic' or the 'ecliptic plane', because all the instances of the line together define or fill out a plane.

Now let us stop time and examine these things : the Sun, the Earth and that line through both. In your mind at least go and sit on that line and think of what you might see. Of course that will depend upon which point on the line you are sitting. If it is inside the Sun or the Earth the answer will be not much and so we will exclude such positions from our thinking. If it is between the Sun and the Earth you will see both bodies on either side of you, that is where a another body might sit and block the sunlight reaching the Earth, that is the realm of solar eclipses ( as seen on Earth's surface ). If you are beyond the Earth they will be on the same side of you and that is the realm of lunar eclipses .... which we will construct the circumstances of next time. ;-)

* Roughly what is that constant for the metric system of units ? For this and all other 'homework' questions, answers to be submitted on the back of a $100 AUD note ! :O]

** Roughly where is this point for the Sun/Earth system ?

*** Take a cone and a plane and use the plane to cut the cone in various orientations. The shape(s) of the cut on the surface of the cone gives rise to the term conic section. But I've missed a conic section case. What is it ?

**** Bonus question : why is the ecliptic plane so named ?

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

- Newton's law's gravitational constant is around 6.7 x 10^{-11} in MKS units

- the centre of mass of the Sun/Earth system is well within the Sun

- there are two conic sections that I missed actually. The first is when I cut the cone with the plane right down the middle from tip, this would be of triangular shape ( a limiting case of hyperbolae ). The second is a cut across the tip of the cone giving only a point : a circle of zero radius.

- the ecliptic plane is where the eclipses happen !

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Total washout with clouds, rain, wind and haze aka a tropical storm. Couldn't get a decent shot of the eclipse, although I have plenty of normal moon shots leading up to it. :-(

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Total washout with clouds, rain, wind and haze aka a tropical storm. Couldn't get a decent shot of the eclipse, although I have plenty of normal moon shots leading up to it. :-(

## Same thing here Mike, Fog

)

Same thing here Mike,

Fog and clouds so with the lunar eclipse it was DARK outside.

We had several deer who think they are sneaking into our apples ........if they only knew it was me picking them and chopping them up so the babies can eat too.

My place is probably the only safe place here.

As usual the next night was clear.

-Samson

## So after some years I'm back

)

So after some years I'm back in FNQ at my usual holiday haunt of Port Douglas and there is going to be a total lunar eclipse next week ! Well it's not so usual as we now have the constant challenge of COVID, but it's been my first opportunity to travel very far for several years. Now according to this page the eclipse will be potentially viewable at my location for almost all of it's phases at around 7pm in the evening of the 8th. That would be seen as rising in the east over the beautiful Coral Sea while the Sun sets in the west. Here's hoping for clear skies and thus some good snaps of the 'blood' moon.

I'll post more later.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

## Mike Hewson wrote: So after

)

Mike Hewson wrote:That would be really cool if things worked out so you can see the whole thing!!

## Hallo Mike! We cross our

)

Hallo Mike!

We cross our fingers for you and this event.

Kind regards and happy crunching

Martin

## Hey Mike! I hope you can

)

Hey Mike!

I hope you can take many good pictures with a real camera, as opposed to the cell phone in you're pocket.

Then when you come back all refreshed from your little jaunt, you can share them with the rest of us on E@H.

;>)Proud member of the Old Farts Association## Thanks for the

)

Thanks for the encouragements. As I've left my digital SLR at home I'll look into hiring a camera for the day. ;-)

The Geometry of Eclipses 1: Let's have a think about why it is that these eclipse events occur at all. For starters let us think of a stripped down version of the solar system. That is, no other planets or moons, including our moon. Just the Sun and the Earth. To an outstanding degree of accuracy we can use Newton's Law of Gravity ( plus F = ma and the equality of action/reaction ) to describe it. For a given pair of objects the force is separately proportional to either body's mass and inversely proportional to the distance between them. There is a comparatively small constant of proportionality to scale the law to our measurements in some system of physical units^{*}. For the moment we may also ignore the Earth's or Sun's rotation about their own axes.Now the Earth and the Sun orbit - around each other - in a shape called an ellipse around their common centre of mass

^{**}. An ellipse is a type of 'conic section' which is a possible type of orbit under Newton's laws. It occurs when there is insufficient energy for either body to escape from the other. A circle is an ellipse with no 'eccentricity' - the number that determines the degree to which an ellipse deviates from a circle. That is, a perfect circle has an eccentricity of zero. Other possible solutions are a parabola ( just enough energy to escape, with zero velocity at infinite separation ) and a hyperbola ( enough energy to escape to infinity with non zero velocity ). So a parabola is the 'edge case' between bound and unbound systems. Having said all of that^{***}, let the orbits be circular which they nearly are anyway. Note that all these conic sections are planar objects.Now, for each moment in time, draw a line starting at the centre of the Sun, going through the centre of the Earth and outwards to infinity. As time goes on the infinitely far away end of that line - or the succession of such lines over time - traces out a path through the pattern of distant stars. This path is called the

e, and please note the highlighted letter 'c' ie. notclipticelliptic. Here there is some slight confusion : ecliptic can also be used as an abbreviation to 'the plane of the ecliptic' or the 'ecliptic plane', because all the instances of the line together define or fill out a plane.Now let us stop time and examine these things : the Sun, the Earth and that line through both. In your mind at least go and sit on that line and think of what you might see. Of course that will depend upon which point on the line you are sitting. If it is inside the Sun or the Earth the answer will be not much and so we will exclude such positions from our thinking. If it is between the Sun and the Earth you will see both bodies on either side of you, that is where a another body might sit and block the sunlight reaching the Earth, that is the realm of solar eclipses ( as seen on Earth's surface ). If you are beyond the Earth they will be on the same side of you and that is the realm of lunar eclipses .... which we will construct the circumstances of next time. ;-)

* Roughly what is that constant for the metric system of units ? For this and all other 'homework' questions, answers to be submitted on the back of a $100 AUD note ! :O]

** Roughly where is this point for the Sun/Earth system ?

*** Take a cone and a plane and use the plane to cut the cone in various orientations. The shape(s) of the cut on the surface of the cone gives rise to the term

conic section. But I've missed a conic section case. What is it ?**** Bonus question : why is the ecliptic plane so named ?

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

## - Newton's law's

)

- Newton's law's gravitational constant is around 6.7 x 10

^{-11}in MKS units- the centre of mass of the Sun/Earth system is well within the Sun

- there are two conic sections that I missed actually. The first is when I cut the cone with the plane right down the middle from tip, this would be of triangular shape ( a limiting case of hyperbolae ). The second is a cut across the tip of the cone giving only a point : a circle of zero radius.

- the ecliptic plane is where the eclipses happen !

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

## Total washout with clouds,

)

Total washout with clouds, rain, wind and haze aka a tropical storm. Couldn't get a decent shot of the eclipse, although I have plenty of normal moon shots leading up to it. :-(

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

## Mike Hewson wrote: Total

)

Mike Hewson wrote:Sorry to hear that Mike, better luck next time!!