the ecliptic

[Iheartquasars]

Hi, im new here but have been lurking for a few weeks . I love some of the collective explainations I have read on here, I was wondering if someone would help explain something to me. I was online reading about the ecliptic and it said:

"as the sun moves along the ecliptic against a background of stars which are there even though you cannot see them against the blue sky, the sun therefore appears also to move north and south of the celestial equator" Here is the website im looking at:
Measuring the sky

Why is this? I did not follow their 'therefore..'. This is probably really simple to you all but I am not getting why the sun appears to rise and set at different spots and traverse the sky at different angles. The second pic on the website shows a schematic of what Im talking about. The sun is fixed so is the earth tilting on its axis to create this, im confused...

Thank you,
Celine

[Guest]

I think it's just because the Earth is tilted , so the sun seems to be different everyday. Also, the Earth revolves around the sun eliptically which means it's not a perfect circle. Hmm, this confuses me a bit too.

[WitheringIntuition]

Oops I forgot to log in

[Tinaa]

Here is a cool picture of how the sun looks throughout the year. I think this picture shows how the sun seems to move north and south of an imagined equator.

[Garvs]

think it's just because the Earth is tilted

This is essentially correct. The ecliptic is the plane of the solar system on which all the planets pretty much orbit. The planets are not on the same plane exactly and all vary by a small number of degrees, Pluto being the wildest, but for the point of explanation ...

It's hard to explain without diagrams, but the Earths axis is tilted 23 degrees in relation to its ecliptic, and it is this that causes the seasons and is why the Sun sits low in the sky during winter and high in summer. Summer is when your hemishpere is tilted towards the sun (in daytime) due to the earths tilt and the sun appears high in the sky. Six months later in winter, your hemishpere is tilted away from the Sun during the day and sits low in the sky while the other hemisphere is enjoying summer.

Also, the Earth revolves around the sun eliptically which means it's not a perfect circle

Also correct. This "aspect" of planetary orbits is known as Keplers 1st Law of Planetary Motion, discovered by Johannes Kepler. The point at which a bodies orbit is closest to the Sun is known as its perihelion, and the farthest point in its orbit is its aphelion. It does not, however, have anything to do with the seasons.

Don't confuse ecliptic with elliptic.

[Iheartquasars]

ok it’s becoming clear now. That beautiful analemma pic combined with the written explanations from you guys makes a lot of sense. So we are not actively tilting back and forth (I was thinking that is some wobble! ) we just keep that angle with respect to the ecliptic as we go around our elliptic path. Making the upper half of the figure eight high in the summer months because we are tilted towards the sun and in the winter the reverse is true. got it thanks!
So, does the ‘tightness’ of the upper and lower segments of the figure eight represent keplers “equal areas in equal times” or is that just cause its an elliptical path. Put another way, what does the widths of the figure eight (wide at the bottom, tight at the top) tell us about our velocity around the elliptic, if anything. just curious

[WitheringIntuition]

Making the upper half of the figure eight high in the summer months because we are tilted towards the sun and in the winter the reverse is true

Yup, and it's the oppisite for anybody in the Southern Hemisphere.

Put another way, what does the widths of the figure eight (wide at the bottom, tight at the top) tell us about our velocity around the elliptic, if anything. just curious

It tells us that we are just revolving at a different time of years, perhaps Fall, or winter. The top ends and bottom ends on that picture represent the different Equinoxes of the year which occur once in spring and once in fall. I'll get back to this later

[Garvs]

So we are not actively tilting back and forth (I was thinking that is some wobble! ) we just keep that angle with respect to the ecliptic as we go around our elliptic path.

Actually, we are wobbling, but it takes about 26,000 years for us to complete one "wobble". It is called precession.

[WitheringIntuition]

Originally posted by Garvs@Jul 11 2005, 03:10 AM

So we are not actively tilting back and forth (I was thinking that is some wobble! ) we just keep that angle with respect to the ecliptic as we go around our elliptic path.

Actually, we are wobbling, but it takes about 26,000 years for us to complete one "wobble". It is called precession.

Oh yeah, I remembered when that happened. I got mad because everything on my desk fell over.