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ralph
2009-Jan-01, 09:59 PM
Hi,

I started this bit of research with an idea that the earths speed around the sun must be changing. I may be wrong here, but with all the variables, I don't see how.

The rough speed is 30 km/sec, taking the year-long mean period, and dividing by the mean distance.
That's the easy answer. I'm looking for detailed research into this, but haven't found it yet.

Reading all the answers more closely, I wondered about the data that lead to those answers.
They all use a steady mass for both the earth and sun. I have problems here.
The earth is recieving more mass all the time, from outside sources, such as dust and meteorites, to the tone of tonnes per year.
I know this is miniscule, compared to the mass of the earth, but it must therefore be increasing.
Is the earth losing mass, and which is greater? (and by how much)
Just on this logic, I'd believe it's gaining.

That's question #1. -and two, and three, I guess.

The sun is converting billions of tonnes of hydrogen to helium every second, and must be losing mass, even with all the mass that crashes into it from the rest of the galaxy.

So how much mass is the sun losing, and at what rate?

That's the next question.

Between these two, it would have to affect the earths orbit, both in distance and speed.

Any references?

tony873004
2009-Jan-01, 11:19 PM
You're right on all counts. But to the precision we compute Earth's velocity, these factors are insignificant.

Jeff Root
2009-Jan-02, 02:23 AM
As Tony says, the mass loss or gain by the Sun and Earth are too small
to be detected by their effects on Earth's orbit.

To the best of my knowledge, the Sun only loses mass, in the form of
neutrinos, sunlight, and solar wind particles (mostly protons and electrons).
Anything smaller than a certain size falling into the Sun would be vaporized
by the intense light and the resulting vapor would be blown away by the
solar wind. I have no idea what the size limit is.

The Earth probably gains faster than it loses.

-- Jeff, in Minneapolis

grant hutchison
2009-Jan-03, 02:16 AM
The sun loses mass at the rate of four million tonnes per second: you'll find that figure confirmed in various astronomy textbooks, or just by Googling on the phrase "four million tons per second".
According to Lewis's Physics and Chemistry of the Solar System, the average rate of increase of the Earth's mass due to meteors is a thousand tonnes per year.

Grant Hutchison