on planets with slow rotations do you think its possible by running or even walking to make the sun come up and then go down(hypothectically of course as i know that i would burn up because of the heat!
Let's assume a few things first.<br /><br />First: We will be on an earth-sized planet orbiting a sol-sized sun at 1 AU. I do this because I already know some numbers for a system like that.<br /><br />Second: The planet is tidally locked, so there is NO apparent rotation at all -- the sun stays in the same place in the sky if you stay in the same place.<br /><br />Third: The planet has its equator line up with the ecliptic (there is no tilt of 22 degrees, like on earth).<br /><br />Fourth: You are on the equator, at sea level, and there are no elevation changes in the way you will be walking.<br /><br />Fifth: I'll add one more thing: There is no atmosphere to cause bending of sunrays. So you can't see the sun "over the horizon".<br /><br />Okay. Let's say you are starting at a spot on the equator where the sun is just below the horizon. The sun has an angular diameter of about 0.5 degrees. So to make it rise to the point where you are seeing the whole thing, you need to walk 0.5 degrees around the planet. This is 1/720th of the way around. Since earth has a circumference of about 25000 miles at the equator, this means you would have to walk about 34.7 miles to cause the sun to come up.<br /><br />If the planet is rotating on you, the job gets harder. Basically, it would have to be rotating slower than you can walk or run.<br /><br />On earth, to make the sun stand still in a similar scenario, you'd have to be going 25000miles/24hr which is about 1040 miles per hour. An velocity added to or subtracted from that would make the sun rise or set for you.
May i ask a similar question? is earth 24hour the ideal rotation speed at current distance to sun? What will happen if it is slower or faster, say o day is 10 hours, or 50 hours. What is the lower and upper limit so life can exist on earth? thanks <div class="Discussion_UserSignature"> </div>
<blockquote><font class="small">In reply to:</font><hr /><p>on planets with slow rotations do you think its possible by running or even walking to make the sun come up and then go down(hypothectically of course as i know that i would burn up because of the heat! <p><hr /></p></p></blockquote><br /><br />You might be interested in a French children's book called <i>Le Petit prince</i>, by Antoine de St Exupery. It's been translated into practically every language on Earth. The Little Prince lives on a tiny asteroid, and though he doesn't generally walk around to see multiple sunrises, he does enjoy watching multiple sunsets by the expedient of getting up and moving his chair forward every so often. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>
A 2 1/2 MPH (or was it KPH?) jog on Iapetus will keep you up with the rising (distant) sun.<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>
Even on fast rotating planets, if you were at a high latitude, you could take your walk and influence sunrise.<br /><br />Earth's moon rotates about 9 miles an hour at the equator. So you could sprint around the moon at the equator and wreak havoc on the sunsets and sunrises. Or, rather than being on the equator, if you were 30 degrees from either pole, where the moon rotates at 3 mph, you could do it by walking. <br /><br />One of the neatest things I've ever seen was an 11 hour sunset. No, I wasn't walking or even driving. I was on a commercial jetliner flying nonstop from Paris to San Francisco. We took off from Paris about 20 minutes before sunset, and landed in San Francisco about 20 minutes after sunset. We literally chased the sunset around the globe, and I had a window seat.
At about a 70 minute day the tropic zone of earth would be about zero g as centrfugal cancels gravity. At the Equator down would be toward space so things not attached such as atmosphere and oceans would form a ring in LEO. All life would parish except far below the surface micro-organisms.<br />With a day about 360 times longer, it would get too hot for land critters, except in the polar regions but micro-organisms far below the surface would survive and critters deep in the ocean.<br />Tide locked to the Sun, there would be a ring of comfortable temperatures about 3000 miles wide with a circufrence of at least 20,000 miles, so there is perhaps no minimum rotational speed. Neil
Wow, did you calculate that? that is amazing, but too extreme, how about 36hours a day, apart that people will rest and work longer in a day perhaps, will our climate, ecosystem etc will still be the same? or 18 hours a day where people will sleep less and work less, means less productivity, what will happen to our civilization? <div class="Discussion_UserSignature"> </div>
I calculated, but not skilfully. That should have been 100 miles per day which is about 4 miles per hour = 6 kilometers per hour. My guess is most creatures, including humans could adapt to a 36 hour day. The high and low daily temperature difference would increase by about 10 %. More people would want two sleep periods per day. Perhaps 20% presently sleep more than ten times per week = babies, small children, the elderly and the Mexican siesta. Neil
I assume that 24hrs/day is the ideal speed of earth rotation, perhaps anything faster or slower may not be comfortable for us on earth, true? Just imagine if the earth suddenly rotate faster, reduce g to 50%, i think i can jump higher than a world record set. -) <div class="Discussion_UserSignature"> </div>
A faster or slower rotation would be more or less unnoticeable gravity-wise:<br /><br />Centripetial acceleration:<br />a = v*v/R<br /><br />v, at the equator, is about 464 m/s<br />R is 6378135 m at the equator<br /><br />a = 464*464/6378135 = .0337 m/s/s<br /><br />Regular gravity is 9.8 m/s/s<br />Acceleration due to rotation is .0337 m/s/s. Remove it or double it; it doesn't make much of a difference.