Perihelion

[JagXKR]

Jan 4th at 6:17am PST we will be closest to the sun. Almost 5 million km closer than on July 3rd later this year. It is surprising to me how many people I have told that have no clue that this happens during January.

https://www.timeanddate.com/astronomy/p ... stice.html

[Jlabute]

I know, and it's been public knowledge for the last 400 years :-)

[maryjane48]

its called earth tilt

[Jlabute]

Tilt is another topic. Perihelion is where the earth is closest to the sun. Opposite of aphelion.
Comes from Greek, peri (near) and Helios (sun).
Due to earths elliptical orbit, there is about a 5 million kilometre difference between the nearest and farthest.

[Sonny Taylor]

its called earth tilt

No. It's called "orbital eccentricity" as explained above. And by coincidence we are closest to the sun when it is winter in the northern hemisphere.

Orbital eccentricity has little discernible effect on seasons because the difference between nearest and furthest distances from the sun over each year is not great enough.

The Earth's 22.5 degree "axial tilt" relative to the Sun also has an interesting relationship with the Earth's Orbital eccentricity. The axis of the earth's rotation (tilt) also actually rotates itself and forms a full circle every 26,000 years. This is called "precession" and it's like the circular wobble in a spinning top.

It means that what we call the north star (currently Polaris) will change over thousands of years. In our time, the axis of Earth's spin points to Polaris in the north. Due to precession, over thousands of years, what we call the north star will change to other stars. But in 26,000 years, Polaris will again become the north star.

Precession of the tilt axis also implies that in about 13,000 years, it will be summer instead of winter in the northern hemisphere during closest approach to the sun, and that will happen when the Earth is roughly on the other side of the sun in it's orbit compared to now.

Even the Earth orbit perihelion and aphelion points will very slowly precess to be at different points around the sun, but now we're probably talking about "geological time" periods for that to happen (not withstanding the moon's 100,000 year effect on eccentricity).


Sheesh I hope I got all that right. I'm open to correction and/or criticism.

[LANDM]

Ok kids, your question of the day......what would the radius of the earth have to be to have an earth tilt of 22 degrees account for being 5 million km closer to the sun at the 50th parallel?
A gold star and a shiny nickel for the first correct answer!

[Sonny Taylor]

Ok kids, your question of the day......what would the radius of the earth have to be to have an earth tilt of 22 degrees account for being 5 million km closer to the sun at the 50th parallel?
A gold star and a shiny nickel for the first correct answer!

Tricky question brings up another question: 50th Parallel north or south?

[LANDM]

Sorry, north.