Looking Down on the ecliptic

[SteveBz]

Hi,

This is probably a very obvious question.

If I'm standing outside at about 51 deg  N.  I had always thought that North was towards Scotland, but actually, it at an angle above my head.  This seems right once I realise that I am halfway up a globe, so N is not the tangent of the globe where I am standing but at another angle, parallel to the axis of rotation of the earth.

Similarly, the sun is in the South at midday, so I have to look South to the ecliptic.  Does pretty much the whole solar system lie on the ecliptic?  The Moon is to the South, as is Mars and Saturn, as was Jupiter when I could see it, so is everything in the Solar system there?

Finally, during the seasons, in the Winter the Sun is above the tropic of Capricorn, so is the ecliptic further South during the day and at Night the objects on the ecliptic should be easier to see (higher above the horizon), and during the summer the Sun is on the tropic of Cancer, so the ecliptic is further South at night and harder to see (lower above the horizon) and also more difficult because of the short nights.

I recall Jupiter was so bright and high it was almost casting shadows in April (2 months before the solstice), as was the Moon but now two months after the solstice, I can hardly see Saturn above my neighbour's trees, nor the Moon.

Is this not right?  What have I not understood correctly?

Back off outside now,

Regards

Steve.

[DRT]

The Ecliptic is the path of the Sun across the sky as observed from Earth. As the Earth it tilted in relation to its orbit around the Sun the Ecliptic moves as the seasons change.

Most solar system objects orbit the Sun in a disk-like system but all of them have slightly tilted orbits in relation to the Sun and their neighbours.

There is very little about this stuff that is straightforward and flat

 

 

[cloudsweeper]

Solar System objects are - more or less - in the plane of the ecliptic.  Where it appears depends on latitude, time of day, and time of year.

Through the year, the Sun appears to move through the zodiacal constellations, which is why they fall on the ecliptic - you can see this on a Planisphere.  Note that when the Sun is in a particular constellation ("sign"), that constellation is behind the Sun during the day and behind the Earth at night, so cannot be seen in the sky.

As Derek says, all this stuff is pretty complicated - it's not easy to picture celestial mechanics in your mind.

Doug.

[SteveBz]

This image is courtesy of Nick Strobel at www.astronomynotes.com seems to suggest the same thing.  In my mind, I keep the Earth's axis North aligned and tilt the Ecliptic, sorry to be so terracentric.

[SteveBz]

So during the Northern summer months, the arrow in the diagram above (showing the angle of rotation of the Earth also pointing North) is slightly oriented towards the Sun during the day, but away from the Sun and the Ecliptic at night, so nocturnal objects further out in the Solar System should be lower in the sky at night during the summer.  During the Northern Winter months (not shown in the diagram), objects further out in the Solar System should be higher in the sky.

So, to answer my earlier question, Jupiter is also 120 degrees further round than it was in April, but why does the Moon seem lower?

[DRT]

1 hour ago, SteveBz said:

So during the Northern summer months, the arrow in the diagram above (showing the angle of rotation of the Earth also pointing North) is slightly oriented towards the Sun during the day, but away from the Sun and the Ecliptic at night, so nocturnal objects further out in the Solar System should be lower in the sky at night during the summer.  During the Northern Winter months (not shown in the diagram), objects further out in the Solar System should be higher in the sky.

So, to answer my earlier question, Jupiter is also 120 degrees further round than it was in April, but why does the Moon seem lower?

Because the Moon doesn't orbit the Earth's equator...

https://en.wikipedia.org/wiki/Orbit_of_the_Moon

 

[bingevader]

10 hours ago, SteveBz said:

If I'm standing outside at about 51 deg  N.  I had always thought that North was towards Scotland, but actually, it at an angle above my head.  This seems right once I realise that I am halfway up a globe, so N is not the tangent of the globe where I am standing but at another angle, parallel to the axis of rotation of the earth.

Nearly. If you drew a straight line between where you are standing and the North Pole, it would go beneath your feet, not above, through the crust to the pole (above Scotland). North isn't at an angle, or parallel, to the axis of rotation, it is the northern point of the axis of rotation (with magnetic north being slightly off from this).

The confusion arises, because you are looking up at the North Star, Polaris, a point on the "celestial sphere", very distant from ourselves. The angle you are describing above your head, is due to this and because of the vast distance.  You are measuring an angle between your position on the earth (flat at that point, or at a tangent to the surface) and the position of Polaris, not the actual North Pole.

Hope that helps.

[brantuk]

The ecliptic is simply the path followed by most of the planets across the sky as they orbit the sun and viewed from Earth. One or two vary on and off it a little due to their orbital tilt, but mostly they're all on the same track. The east and west ends of the ecliptic move up and down the horizon with the seasons.

I wouldn't worry about Scotland - they just confuse the issue like they did brexit lol. It's geographic north anyway and has no bearing on celestial positioning.

The celestial pole is the nearest star to the axis of Earth's rotation - it's actually just a little off center cos Earth wobbles as it spins which is why your polar scope places it in the small circle, and moves around the larger circle circumference nightly. In the southern hemisphere the nearest star to Earth's axis is in the Southern Cross.

Hope that helps - but I fear it just confuses further lol. It's hard to explain but easier to experience when you stay out all night with the scope watching it all happen.

 

 

 

 

 

 

[Floater]

3 hours ago, brantuk said:

I wouldn't worry about Scotland - they just confuse the issue like they did brexit lol.

Hmmm. A bit off-axis there, I fear. ?

[cloudsweeper]

18 hours ago, SteveBz said:

 

Finally, during the seasons, in the Winter the Sun is above the tropic of Capricorn, so is the ecliptic further South during the day and at Night the objects on the ecliptic should be easier to see (higher above the horizon), and during the summer the Sun is on the tropic of Cancer, so the ecliptic is further South at night and harder to see (lower above the horizon) and also more difficult because of the short nights.

 

A play with the Planisphere seems to confirm that the Ecliptic is higher in winter, and lower in the summer.

Doug.