Is It True?

[LukeSkywatcher]

The other night on Stargazing Live, the lovely Lucie Green said that the four main moons of Jupiter only ever align in a row on the right side of the planet every 6 yrs.

She made quite a big issue of this.

I know for a fact that i have seen all 4 moons in a line on the right side of the planet more then once since ive owned telescopes since 2007.

Comments?

[Steve Ward]

Of course she's right ...  

Exactly in line every six years , you only get to see the moons occult themselves as they are doing in 2015 when the Jovian ecliptic is exactly aligned to Earth .

You may have seen them in a 'line' before , but not a 'straight' line .

[Astronigel]

I noticed that on the program also.

And seen them all to one side the same as you.

So I guessed she meant maybe all in correct sequence, innermost moon closest and so on.

[Cath]

Maybe she meant when they all line up on a straight line outer to inner planetary moon? .. I don't mean from our point of view, I mean from the moons point of view.

Care say for sure.

[LukeSkywatcher]

I noticed that on the program also.

And seen them all to one side the same as you.

So I guessed she meant maybe all in correct sequence, innermost moon closest and so on.

That would make more sense.

[JamesF]

I did wonder about this when she said it and I don't think it was ever made specifically clear what she meant.

Certainly if you set up Stellarium for around 11pm on 18th March 2015 the moons trail out nicely to the west of Jupiter in order of their orbital distances.  I know I've seen them lined up all on one side of the planet before now so I have to assume that in such cases we're "seeing all the right moons, but not necessarily in the right order".

James

[Stu]

I did wonder about this when she said it and I don't think it was ever made specifically clear what she meant.

Certainly if you set up Stellarium for around 11pm on 18th March 2015 the moons trail out nicely to the west of Jupiter in order of their orbital distances. I know I've seen them lined up all on one side of the planet before now so I have to assume that in such cases we're "seeing all the right moons, but not necessarily in the right order".

James

There's a Morecambe and Wise sketch in there somewhere James [emoji6]

[JamesF]

There's a Morecambe and Wise sketch in there somewhere James [emoji6]

Quite deliberately so, but I did wonder how many people might pick up on it

James

[Peter Drew]

Separates the men from the boys, agewise. 

[LukeSkywatcher]

Separates the men from the boys, agewise. 

Call me a boy.

[MarsG76]

Of course shes hot... I mean right... the line up only happens every 6 years.. the other times you have seen the moons in a line were not in a perfect line....

[Stub Mandrel]

I thought the orbital resonances of Ganymede, Io and Eurpoa mean they can NEVER be aligned in a straight line on the same side of Jupiter, but line up two on one side, one on t'other every two Io orbits.