Earth

[vijaywantstoknow]

Being on Earth, how to calculate the mass, speed of rotation and speed of revolution of Earth?

 

[MeteorWayne]

Well, A revolution takes a year, so that's easy <img src="/images/icons/smile.gif" /><br />Rotation? Well look at a star in the sky and see how long it takes to get back to the same spot. 24 hours. (a 4 minute adjustment is necessary since we've gone approximately 1/365.24 of the way around the sun in that day).<br /><br />Mass can be calculated from the earth's size and the force of gravity, the orbit of the earth, and other methods. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[weeman]

Mass might be one of the most difficult to calculate. Measuring the circumference of Earth might get you on the right track towards measuring its mass. This link below is an interesting home experiment to measure Earth's circumference! This was an activity given to my Astronomy class. <br /><br />http://www.mscd.edu/~physics/astro/activities/activity2.htm <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[docm]

Eratosthenes first came up with numbers very close to Earth's actual radius (within a few percent) in 230 BC, and calculating its volume followed from that. <br /><br />Once Galileo measured the acceleration due to gravity at Earth's surface and Cavendish measured Newtons gravitational constant things progressed rapidly. In 1798 Cavendish published that the average density of the earth is 5.48 times that of water. The modern value is 5.52 times the density of water. Not bad.<br /> <div class="Discussion_UserSignature"> </div>

 

[vijaywantstoknow]

Thanks.<br />But how do we know that it takes 365.24 days for one revolution?<br />In case of calculating a day, the earth and the star's position (the star we use for comparision), may not have changed very much, but for a year, definitely it should have.<br />Moreover, i think we are not travelling the same distance for every revolution.<br /><br />Is the speed of revolution of earth is constant?<br />Is this formula correct? speed of revolution = distance travelled for one revolution / time taken for one revolution<br /><br />Does all the three (speed of revolution, distance travelled by earth around sun every year, time taken for one revolution)<br />properties change every year?<br /><br />

 

[docm]

Neolithic man knew the length of the year quite accurately, which is why they built Stonehenge and other such solar observatories. <br /><br />All it takes is a high rock with a hole in it for the sunrise to shine through and a bunch of other rocks to mark the position of the light cast on the ground on each successive day. When the sun returns to rock #1 you count rocks and that's the length of the year in days. <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

THe motion of most stars in a year is almost immeasurably small. There are a few exceptions, the largest proper motion is for Barnards star, about 10 arcseconds per year. SO the effect would be much less than a minute, even using that star as a reference. Not a factor.<br /><br />While the distance and path we travel is not identical every orbit (due to the subtle shift in the center of mass of the solar system, or barycenter, as the planets, but mostly Jupiter and Saturn move around, and the earth and moon orbiting their own barycenter) it's close enough so that once again, the difference is almost too small to measure. So we do travel almost exactly the same distance every orbit.<br /><br />The earth's average speed (the formula you gave is fine) does not change, however, following Keplers laws, the orbital speed is fastest near perihelion in early January, and slowest in early July near aphehelion.<br />But the average stays the same from year to year. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[qso1]

VijayWantsToKnow:<br />But how do we know that it takes 365.24 days for one revolution?<br /><br />Me:<br />Easiest way to determine the revolution, at least down to the year is look at certain constellations like Orion. They are in the same place at the same time year after year. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[vogon13]

After all, earth moves very nearly one degree around the sun every day. We can routinely measure astronomical angles down to an accuracy of an arc second easily, and if you look at quasars with VLBI, micro arcseconds.<br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[qso1]

You betcha.<br /><br />I have actually looked at Orion from one year to the next and even at the planets and looking at Jupiter, could tell where it should be in 3 years based on its orbital period. I don't go down to micro arcseconds of course, but you can get down to arc seconds. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[MeteorWayne]

Once you really start to watch the sky a lot, the cycles become obvious and beautiful.<br /><br />Think how much easier and profound that was for earlier man with no light pollution, TV, or SDC <img src="/images/icons/smile.gif" />, and a life that required understanding the ebb and flow of our environment.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[qso1]

I used to have a backyard telescope and observed the sky quite a bit but where I live even in the 1970s light pollution was a problem. Nowadays I sometimes look at the sky from where I work when I'm on lunch which is around 3 A.M.<br /><br />I can imagine how early man would see the cycles. Most folks today glance at the night sky and don't give it much thought. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[spacecrusader]

What if the earth just stopped moving? Would we be thrown into space,<br />exaple- we were not buckled into a seat of a car(earth) and the car crashed and we flew through the windshield(outerspace)?

 

[ashish27]

the entire earth will be flooded with ocean water and we will be drowned to death. we won't be thrown into space because gravity would still be there!

 

[MeteorWayne]

Why would we be flooded with ocean water?<br /><br />If it is because the water would keep moving while the earth stopped, then all the objects on the suface would be affected the same way.<br /><br />So, while gravity would keep us from flying into space, we would still be traveling at the same speed we were before the earth stopped, which would lead to an unpleasent parabolic trajectory <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[a_lost_packet_]

Yup. We'd go from "here" to "there" at somewhat unsafe speeds... <div class="Discussion_UserSignature"> <font size="1">I put on my robe and wizard hat...</font> </div>

 

[MeteorWayne]

Along with cars, cows, buildings, birds and bees <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[Kalstang]

<font color="yellow">Yup. We'd go from "here" to "there" at somewhat unsafe speeds... </font><br /><br />Love the understatement there. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <font color="#ffff00"><p><font color="#3366ff">I have an answer for everything...you may not like the answer or it may not satisfy your curiosity..but it will still be an answer.</font> <br /><font color="#ff0000">"Imagination is more important then Knowledge" ~Albert Einstien~</font> <br /><font color="#cc99ff">Guns dont kill people. People kill people</font>.</p></font><p><font color="#ff6600">Solar System</font></p> </div>

 

[Smersh]

If the earth <i>suddenly</i> stopped moving then yes, certainly many of the scenarios described in this thread would be quite plausible I believe.<br /><br />However, a gradual slowing, say over a period of a few months, would be an entirely different thing wouldn't it?<br /><br />The Earth is slowing very gradually anyway I believe, although I think it'll be a few billion years before it stops altogether (please correct me if I'm wrong of course as I'm sure people will correct me on this if it's wrong <img src="/images/icons/wink.gif" /> )<br /> <div class="Discussion_UserSignature"> <h1 style="margin:0pt;font-size:12px">----------------------------------------------------- </h1><p><font color="#800000"><em>Lady Nancy Astor: "Winston, if you were my husband, I'd poison your tea."<br />Churchill: "Nancy, if you were my wife, I'd drink it."</em></font></p><p><font color="#0000ff"><strong>Website / forums </strong></font></p> </div>

 

[spacecrusader]

Well How fast is the earth moving?

 

[yevaud]

Orbital Velocity = 29.8 km/s <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[MeteorWayne]

Yevaud has give you the average orbital velocity.<br />It actually varies slightly throughout the year being highest in the beginning of January when the earth is closest to the sun, and slowest in July when we are furthest away. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[dragon04]

I should think that if Earth encountered a force that could immediately "stop" the Earth, that being flung off of it would be the least of our worries.<br /><br />I'd guess that the entire planet would be instantly pulverized into itty bitty parts and pieces. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[lukman]

infact we will feel more gravity if the earth is not moving, why i feel that i have seen the exactly identical question before? <div class="Discussion_UserSignature"> </div>

 

[schmack]

infact we will feel more gravity if the earth is not moving,<br /><br />Why would we feel more gravity if the earth stopped moving? does inertia have no effect on us when we're on a planet. <div class="Discussion_UserSignature"> <p><font size="4" color="#ff0000"><font size="2">Assumption is the mother of all stuff ups</font> </font></p><p><font size="4" color="#ff0000">Gimme some Schmack Schmack!</font></p> </div>