# Does a meteor's direction change between country or latitude?

So here is the question me and a friend of mine from Norway we saw a meteor but que said he saw it in the opposite direction as me and I was looking from spain, does that make any sense? Or we should see it going the same direction? Thanks in advance

• Welcome to astronomy SE! Please edit in more details: In which direction did he see it, in which direction did you see it? – B--rian Mar 10 at 13:32
• If you were 100 km from the North pole but on opposite sides of it and it passed directly over the pole, then one of you would see easterly motion and the other westerly.. Otherwise, I don't think it's possible. – uhoh Mar 10 at 14:20
• Maybe you were just looking the opposite direction. – Anonymous Mar 11 at 3:20
• ...assuming "direction" is azimuth (e.g.south, west, east, north...) but answers now explain that if it's left-right the answer can be different. You haven't specified how the observers report direction yet. – uhoh Mar 11 at 3:45

If you see the same meteor, it of course only has one path - even while the apparent movement differs for different observers. What you basically do in that case is triangulation - which you could use with your known geographic location (and time for the observations, and the direction horizontally and vertically) reconstruct the flight path. That's a method which actually is used to identify meteors and and tracking them, e.g. via the fireball network.

Is it possible that you saw the meteor given your geographic separation? (note 11 March: This paragraph is heavily revised and comes to the opposite conclusion with the right trigonometry)

Given the mentioned separation between Norway and Spain, we talk of a few thousand kilometres. The typical height at which you see a meteor is between 50 and 100km. The curvature of Earth then makes sure you don't see the same meteor when you are too far apart - but it might be still just right here:

Madrid and Oslo are about 2000km apart, the Earth's circumference is about 40000km. The earth's radius is $$r_E = 6371$$km which allows us to calculate the angle $$\alpha$$ between those as seen from Earth's centre: $$\alpha = 0.31$$ (radians). With that angle we can calculate the height an object must be at when we look horizontally and just see it at the horizon (laying on the floor makes it easy to calculate), given it's separated by the angle $$\alpha$$:

$$d_s = r_E\cdot tan\alpha$$ and $$\frac{h+r_e}{\sin 90°} = \frac{d_s}{\sin\alpha} = \frac{r_e\tan\alpha}{\sin\alpha} = \frac{r_E}{\cos\alpha} = r_E \sec\alpha$$ so that $$h = \frac{r_E}{\cos\alpha}-r_E$$ Now if you enter the angle between Oslo and Madrid you get a height of about 79km for an object passing half-way (thus at half the angle to each). So it might have been that very same meteor if it was very close to the local horizon. Given that this estimation is pessimistic as it ignores observer height, things get a bit better if you assume that you stand on your feet, on a building or even a mountain. Either way, the meteor will have been close to the horizon for both of you, and very likely for one travelling left to right, for the other observer right to left.

• This formula is incorrect, the correct formula should be h = r_E (sec(\alpha / 2) - 1) to get the minimum height of an object that would be visible by two observers separated by an angle alpha. Plugging the numbers in for this situation gives a minimum altitude of ~70 km. – Kyle Mar 11 at 7:47
• @Kyle you are so right! And it somewhat changes the answer. I actually noticed during breakfast and was just editing it when you wrote your comment. Thanks :) – planetmaker Mar 11 at 8:47

Yes, but it depends on your reference system. If the meteor was moving East to West over England, it would appear to be going Left to Right from Norway, but Right to Left from Spain.

• This is a good supplemental point, and by extension, this can apply to a single person standing (or laying down) an looking straight up. It could be left-right or right-left or even forward or backward (up or down). – uhoh Mar 11 at 3:41

Yes, if the object is moving between the two of you then your reference systems are different. For example two people standing on opposite sides of a river. One sees it flowing from left to right, the other sees it flowing from right to left.

The river, or meteor, has not itself changed direction, but you'll each describe the direction differently if you're using spatial reference systems relative to yourself.

• This seems similar to the other existing answers. What makes yours different? – slowerthanstopped Mar 11 at 3:01
• @slowerthanstopped I think it is much simpler to visualise something on the scale of a river which is clearly flowing one way without having to deal with compass directions or geography. I judged the target audience as needing something that makes it very clear in layman's terms – Craig Mar 11 at 7:31

No, they do not change direction when they pass over country borders or latitude. It is just based on where your positions are relative to the meteor.

• "Papers, please?" I would not want to encounter customs officers with such powers. – Camille Goudeseune Mar 11 at 4:26
• @Camille - the meteor might have been trying to avoid just such customs officers ;-) – Eric M Mar 12 at 1:20