[thedoc (OP)]

Nadia Adam  asked the Naked Scientists:
   Hello, what is the shape of earth's orbit.  Is it in shape of spirals  continuously  moving in some direction.  If so one side of spiral must be tilted  nor not.
   Thanks

 
What do you think?

[PmbPhy]

Nadia Adam  asked the Naked Scientists:
   Hello, what is the shape of earth's orbit.  Is it in shape of spirals  continuously  moving in some direction.  If so one side of spiral must be tilted  nor not.
   Thanks

 
What do you think?

The shape of the Earth's orbit is slightly elliptical. See:
http://www.cso.caltech.edu/outreach/log/NIGHT_DAY/elliptical.htm

It's close to being circular but its not.

[RD]

The shape of Earth's orbit is not constant : the eccentricity of Earth's orbit varies over long time-scales due to gravitational influence of other planets ...

 [ Invalid Attachment ]
https://en.wikipedia.org/wiki/Milankovitch_cycles

[evan_au]

what is the shape of earth's orbit?

The answer depends on the timescale over which you measure it:

• If you look on a 1 second timescale, you could treat it as a straight line
• If you look on a 100 year timescale, you could consider it an ellipse (almost a circle) - but with some small wiggles due to the Moon
• If you look on a 10,000 year timescale, several of the longer-term Milankovitch cycles slightly affect the eccentricity and orientation of the orbit in space
• If you look on a timescale of billions of years, the orbits can become chaotic, with planets swapping positions, or even being flung right out of the solar system (or into the Sun).

Is it in the shape of spirals?

It is true that the Sun is losing mass through the Solar wind. This means that the Earth's orbit is slowly spiraling outwards - it is expected to drift outwards to somewhere near Mars in about 5 billion years. But this won't be enough to stop it being scorched to a cinder as the Sun enters the red giant phase.

It is true that the Earth/Sun system is continuously radiating gravitational waves (about 200W). If allowed to continue for a very long time (hundreds of billions of years), this would result in the Earth slowly spiraling slowly closer to the Sun. But this effect is negligible compared to the meteorites hitting Earth every day (even sandgrain impacts produce MegaWatts - for an instant).

[jeffreyH]

In the strictest terms, assuming we are in an inertial frame of reference, the sun, planets and the fixed stars can be thought of as orbiting us. Extending this to a frame of reference centred of our central black hole the earths orbit can be considered to be a flattened spiral tracing a course around the galaxy. It all depends upon the selection of reference frame.