View Full Version : Jupiter rotation

scorpio0611

2009-Mar-10, 06:06 AM

hi there....

i'm student in sydney and now i have project to do, which is to calculate jupiter rotation by seeing its red spot..

Does anyone know how i should start??

how can i measure the rotation by seeing red spot? is there any formula??

please help me...

thanks

Start by observing Jupiter and taking measurements?

slang

2009-Mar-10, 07:47 AM

Welcome to BAUT, scorpio0611!

how can i measure the rotation by seeing red spot? is there any formula??

One hint: you need to see it more than once.

scorpio0611

2009-Mar-10, 09:34 AM

yes, start observing jupiter red spot and taking measurement

thanks a lot...

astromark

2009-Mar-10, 10:12 AM

The massive planet Jupiter is a gas giant. By observing features moving across the face of Jupiter we can measure her rotation and have. Observation has revealed that the great red spot is seen to move across the planet. Slower than features visible nearer to the equator. Having access to a telescope that is situated and good enough to see this may not be available to you. There are web sites that will reveal the information you want for your project. All you need to do is read it.

scorpio0611

2009-Mar-10, 10:28 AM

thanks astromark.. i have tried to find information from many web sites but still, i can't find out how to measure the rotation by seeing the red spot... Recently, i visit the slooh website, but i still cannot get the picture of red spot which can lead me to next step...

by the way, after i observe the red spot, what is my next step??

Peter B

2009-Mar-10, 10:42 AM

thanks astromark.. i have tried to find information from many web sites but still, i can't find out how to measure the rotation by seeing the red spot... Recently, i visit the slooh website, but i still cannot get the picture of red spot which can lead me to next step...

by the way, after i observe the red spot, what is my next step??

G'day scorpio

I'm no astronomer, but a couple of things occur to me.

The simple one is this: in the course of one Jupiter day, the Red Spot will return to the same location.

The complex one is this: with a bit of trigonometry, you could calculate how much of a rotation the spot has completed in a limited period of observation.

Neverfly

2009-Mar-10, 10:57 AM

Ok, let's clear up a few things, just to reduce any confusion...

Two hints:

One- the GRS does, indeed, move around the planet Jupiter. So you can't get dead accuracy on how fast Jupiter rotates by observing the spot. However, you can get fairly accurate because the GRS doesn't move quickly. So for a quick, back of the envelope calculation of how fast Jupiter rotates, the GRS is a fair enough reference point.

So all you really are doing is considering the GRS as a "fixed" point. As you observe at timed intervals, you will reach two basic figures: How much time has passed and how far the GRS has moved.

Simple no? Middle School algebra is sufficient.

Two- The Planet Jupiter rotates very fast. So if you get a surprising answer, don't be alarmed.

Jupiter is king of the solar system and it dresses to impress and doesn't do anything small. It's a bit like Texas in that regard...:p

scorpio0611

2009-Mar-10, 10:59 AM

thanks peter....

now, i got a bright idea about what i'm doing... However, could u tell me more specific how to calculate it by trigonometry??

scorpio0611

2009-Mar-10, 11:05 AM

Thanks neverfly...

but how i calculate the distance GRS travel in a particular intervals? can i find out what is the speed of the rotation?

does anyone have suggestions which web site i have to visit to get more information? thanks

Neverfly

2009-Mar-10, 11:12 AM

Thanks neverfly...

but how i calculate the distance GRS travel in a particular intervals? can i find out what is the speed of the rotation?

does anyone have suggestions which web site i have to visit to get more information? thanks

Any website on Jupiter can tell you the answer. heck, most of us replying could.

But the problem is- This is a school assignment and the purpose of such is to tune your brain into figuring things out.

Now.. to help you out a bit.

First, stop looking at it like a complex problem. Like writers block, many folks look at math and are immediately daunted because they assume that it's more complex than it really is.

Second, figure out what numbers you need to know.

If you are going to figure out how fast something is moving- what numbers do you need to know to figure it out?

EDG_'s post, the second reply, was dead on target.

Jeff Root

2009-Mar-10, 11:13 AM

I assume that you are taking a college-level introductory astronomy

course. Is that correct?

What instrument will you use for the observations?

How much time have you been given to complete the observations?

Are you aware that Jupiter is currently a morning object, rising shortly

before the sky starts becoming light?

-- Jeff, in Minneapolis

tusenfem

2009-Mar-10, 01:22 PM

Just to be nerdy: There are 3(4) coordinate systems for Jupiter with their own rotational period. I hope I get them in the right order, but as I am away, I cannot give all the details:

System 1 is for latitudes 10 degrees north and south of Jupiter's equator - the rotation is 9 hours 50 minutes.

System II is for latitudes north and south of this region, and the rotation rate is 9 hours, 55 minutes.

System III, measures the rotation speed of Jupiter's magnetosphere and is usually considered the official rotation rate at 9 hours, 55 mins, 29,71 sec.

And then there is a subsystem in system III, which is not constant in phase (it jumps), but is in period, called system IV at even a slighly longer period (about 3%), and its origin is basically unknown.

Bob B.

2009-Mar-10, 01:45 PM

by the way, after i observe the red spot, what is my next step??

What do you think is the next step? Hopefully you gave the problem some thought before asking the question. How far did you get? Explain your thought process to this point. We can probably guide you but this is your problem to solve; we would do you a disservice if we just gave you the answer.

Peter B

2009-Mar-10, 02:20 PM

thanks peter....

now, i got a bright idea about what i'm doing... However, could u tell me more specific how to calculate it by trigonometry??

Okay, but remember, I'm not an astronomer, and it's a lo-o-o-ong time since I looked at this sort of maths, so beware that others may pick me apart. Also, this is only a thought experiment, and it mightn't work in practice.

1. As Jupiter rotates, objects appear on one side of the planet, move across its face and disappear off the opposite side.

2. Jupiter is roughly a sphere. This means that any object moving across its face will move laterally most slowly near the horizons and most quickly near the centre of the face. This means that you can't simply see how far the GRS moves in a given time and multiply that up to work out the rotation time.

3. Observe the GRS several times, recording where you see it and when. In recording where you see it, make a note of how far it is from the horizon directly to its left and right, as below:

(o----) > (-o---) > (--o--) > and so on...

4. Draw a circle on a piece of paper to represent Jupiter as seen from above its North Pole, with centre C. The circle therefore represents Jupiter's equator as seen from above. Draw a horizontal line through the centre of the circle. You, the observer, are at the bottom of the page. Mark on the horizontal line the various points where you saw the GRS (T1, T2, etc). Draw a vertical line from each point down to the circle (T'1, T'2, etc). Mark the times you saw the GRS at these locations.

5. Measure the angle T'1-C-T'2. Find out what proportion of a complete circle that angle is.

6. You should be able to work it out from there.

7. Check your answer using various GRS locations and times.

Actually, now that I think about it, that didn't involve any trig.

And remember, no guarantee that'll work, or even that it's the simplest idea going around.

Peter B

2009-Mar-10, 02:25 PM

Thanks neverfly...

but how i calculate the distance GRS travel in a particular intervals? can i find out what is the speed of the rotation?

does anyone have suggestions which web site i have to visit to get more information? thanks

You seem to be thinking in terms of distances. Think instead of angles.

Watch a merry-go-round spinning. How would you calculate how long it takes to complete one revolution? How would you calculate that figure if you were only allowed to watch the merry-go-round for five seconds?

Neverfly

2009-Mar-10, 04:11 PM

You seem to be thinking in terms of distances. Think instead of angles.

Watch a merry-go-round spinning. How would you calculate how long it takes to complete one revolution? How would you calculate that figure if you were only allowed to watch the merry-go-round for five seconds?

As I said; back of the envelope.

It's enough to get past the daunting appearance. Once that's done, he can move into the more accurate depth as you have started to describe.

I was kinda trying to keep it simple...

Jens

2009-Mar-11, 08:52 AM

hi there....

i'm student in sydney and now i have project to do, which is to calculate jupiter rotation by seeing its red spot..

Just out of curiosity, do you have access to a telescope? You can't see the red spot with the naked eye, unless you have very, very, very, very good eyes! :)

astromark

2009-Mar-11, 09:34 AM

Just to be nerdy: There are 3(4) coordinate systems for Jupiter with their own rotational period. I hope I get them in the right order, but as I am away, I cannot give all the details:

System 1 is for latitudes 10 degrees north and south of Jupiter's equator - the rotation is 9 hours 50 minutes.

System II is for latitudes north and south of this region, and the rotation rate is 9 hours, 55 minutes.

System III, measures the rotation speed of Jupiter's magnetosphere and is usually considered the official rotation rate at 9 hours, 55 mins, 29,71 sec.

And then there is a subsystem in system III, which is not constant in phase (it jumps), but is in period, called system IV at even a slighly longer period (about 3%), and its origin is basically unknown.

Can you not see that the need to actually tell the answer was being carefully avoided...

Attempting to explain what and how to actually solve the question. Thinking for one's self is a important part of self awareness and esteem. Most of us clever clogs astronomers do actually know where and how to time the rotation observed. We think as one in regard to telling the answer.... please remove your gumboots when coming in here...:)mark the astronomical gnome.

scorpio0611

2009-Mar-11, 10:18 AM

yes, thanks everyone...

anyway, can i find the distance between red spot after several hours using parallax formula?? then i can find out the angle, which then i can calculate its time of rotation..

i don't have any telescope, but my teacher suggest me to use slooh website as my assistance. However i can't find good picture of jupiter in there that i can use.

Jeff Root

2009-Mar-11, 11:56 AM

I'm not familiar with how Slooh works. Are you using a scope in the

Canary Islands? I see that Slooh just added a second observatory in

Chile, and expects to add a third near Wandong in Victoria very soon.

If you are using a scope in the Canary Islands in real time, then you

will be observering at about 4 PM your time, give or take an hour or

two. Have I got that right? Jupiter will be visible for maybe 2-4 hours

from the time it rises until the sky becomes too bright to make out the

Great Red Spot. Presumeably, the GRS is currently on our side of

Jupiter during at least part of that 2-4 hour period.

anyway, can i find the distance between red spot after several

hours using parallax formula??

The distance between the the GRS and what? Jupiter's centerline?

I suspect that what you will actually measure is the number of pixels

between either the center or one edge of the GRS and the center

of Jupiter's disk.

If you are permitted to use a reference value for Jupiter's diameter,

you can use it to calculate the distance in kilometres that the GRS

moves between images. If you are not permitted to use a reference

value, you will need to determine Jupiter's diameter from the images

and the characteristics of the scope optics and electronic imaging

system, first.

Have you already done that?

then i can find out the angle, which then i can calculate its time of

rotation..

You *could* instead, calculate the change in angle directly, rather

than calculating the distance in kilometres first. It depends on what

you want and what your instructor wants you to do.

i don't have any telescope, but my teacher suggest me to use slooh

website as my assistance. However i can't find good picture of jupiter

in there that i can use.

I'm not familiar with the Slooh website. Are you hoping to find images

of Jupiter previously taken by other observers? Or did you try to use

a telescope in real time, and found that the GRS was not visible at

that time?

-- Jeff, in Minneapolis

Peter B

2009-Mar-11, 12:00 PM

yes, thanks everyone...

anyway, can i find the distance between red spot after several hours using parallax formula?

then i can find out the angle, which then i can calculate its time of rotation..

I don't know for sure, but I don't think so. Parallax involves measurements of an object against a distant background. That's not what the GRS is doing.

i don't have any telescope, but my teacher suggest me to use slooh website as my assistance. However i can't find good picture of jupiter in there that i can use.

I get the impression you still don't understand the principles involved in reaching your answer. Do you understand the merry-go-round example I mentioned before? And out of interest, would you be willing to tell us how old you are?

Bob B.

2009-Mar-11, 01:23 PM

anyway, can i find the distance between red spot after several hours using parallax formula??

Parallax formula? No, that’s applicable here.

What you need to know is the angle through which the Great Red Spot rotates between successive observations. Using Peter B’s merry-go-round analogy, the angle can be observed by looking down on the merry-go-round from above, but you’re observing the merry-go-round from the side. Observing the merry-go-round from the side, what measurements can you make that will allow you to determine what the angle looks like from above?

By the way, is this an astronomy assignment or a math assignment? I think we need to know the gist of the exercise to properly assist you.

scorpio0611

2009-Mar-11, 10:53 PM

Can I use cosine "formula" to calculate the angle because I know the radius of Jupiter and the distance between two positions of red spot?

And i still don't understand the principle of merry-go-round.

Actually i want to use slooh to reserve a mission, but at the moment the reservation is not available, so i decide to find jupiter's pictures which can help me..

Do you have any good pictures of jupiter with GRS in several hours interval??

slang

2009-Mar-11, 11:27 PM

Do you have any good pictures of jupiter with GRS in several hours interval??

Try searching Voyager or Galileo image archives (google should take you there easily). I think both have taken images that were later assembled into animated sequences. Many archives include the exact time and date when a picture was taken.

Bob B.

2009-Mar-11, 11:32 PM

Can I use cosine "formula" to calculate the angle because I know the radius of Jupiter and the distance between two positions of red spot?

You're getting close. You need to know a little more than just the distance between the two observations of the GRS. The distance the GRS appears to move in a given time period is not constant. For instance, will the GRS appear to move faster when it is near the limb or near the center of the disc?

And i still don't understand the principle of merry-go-round.

Observing a horse as it moves around a merry-go-round is analogous to observing the GRS as it moves across the face of Jupiter. The technique used to determine the rotation period of Jupiter can also be used to determine the period of the merry-go-round.

scorpio0611

2009-Mar-12, 10:50 PM

i thought the GRS will move faster when it is near the limb, am i right??

Now I will tell you my steps to find rotation

First I measure the distance between two positions GRS

Then I use similar triangle to find the radius of the disc that GRS movement created.

Afterthat I use "cosine" formula to find the angle

But my work is correct only when the disc is circle, and u said that it is not a circle maybe an ecllipse.

So is my process correct? I did a rough work and got a rotation of 11.5 hours.

slang

2009-Mar-12, 11:23 PM

So is my process correct? I did a rough work and got a rotation of 11.5 hours.

I can't say anything about your process, but check post #13 from tusenfem..

Jeff Root

2009-Mar-13, 04:32 AM

i thought the GRS will move faster when it is near the limb, am i right??

The opposite. Its apparent motion is fastest at the center of the disk.

The term "simple harmonic motion" refers to what you see. Google

shows many useful sites among hits on the term. Wikipedia is first:

http://en.wikipedia.org/wiki/Simple_harmonic_motion

The second animation (out of five) on that page has a timing problem

on my computer, but that may just be my computer.

Another page has a Java animation that works even on my computer:

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=148

Now I will tell you my steps to find rotation

First I measure the distance between two positions GRS

In my last post I guessed that what you will actually measure is

the number of pixels between either the center or one edge of

the GRS and the center of Jupiter's disk. Is that what you are

measuring? Your very sketchy description is unclear.

Then I use similar triangle to find the radius of the disc that GRS

movement created.

It isn't clear to me what triangles you constructed, what points

you measured, or even what you mean by "radius of the disk".

After that I use "cosine" formula to find the angle

But my work is correct only when the disc is circle, and u said that

it is not a circle maybe an ecllipse.

That is "ellipse", of course. :) Did you get that info from elsewhere?

I don't see where anyone above said the disk would not be a circle.

As seen from Earth, Jupiter is always nearly fully-illuminated, but

one edge can be in shadow. Jupiter's equatorial radius is 1/15th

greater than its polar radius, but if you are only measuring parallel

to the equator, that should not be a concern here.

So is my process correct? I did a rough work and got a rotation of

11.5 hours.

You need to describe your process in more detail. Define your

terms when there is any possibility of ambiguity, such as whether

you are referring to a measurement in pixels, kilometres, degrees,

radians, or some other unit.

-- Jeff, in Minneapolis

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