# Interpreting Spectra for Jupiter's Rotational Speed

In summary, the conversation is about interpreting a spectra to calculate the rotational speed of Jupiter. The computer indicates a doppler shift, but the speaker is having trouble seeing it in the photograph. They discuss the orientation of the slit and the expected slant of the lines due to the rotation of Jupiter's atmosphere. The resolution of the spectrum is small and it is difficult to see the shift. They also mention the identity of the central line and the possibility of sunlight reflection.
I got a spectra I need to interpret. It is used to calculate the rotational speed of Jupiter. However, altough the computer indicates the doppler shift, I don't see anything (see photograph). I wonder if anyone could enlighten my stalled mind?

I suppose when I figure out the wavelenght change I just plug it into the doppler formula and get the velocity? (12.66 km/s from data table)

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What you're seeing is frequency in the horizontal direction and position along the slit in the vertical direction. I don't know which lines you're looking at, but based on the orientation of the slit, you'd expect them to be slanted by the rotation of the planet's atmosphere. That is, at one end of the slit you'll have a velocity away from your line of sight and, therefore, a positive Doppler shift. At the other end, the atmosphere would be moving towards you, so it would exhibit a negative shift. The net result would be a line slanted from one direction to the other. Unfortunately, the resolution of their spectrum is very small. At 12.66 km/s, you'd expect a shift of order:

$$\frac{\Delta \lambda}{\lambda}=v/c=4.22 \times 10^{-5}$$

If your spectrum is in the visible, then you're probably looking at wavelengths of order 5000 angstroms, so you should see a shift of about 0.2 angstroms. However, if the scale they list on the image is to be believed, then each pixel represents 1 angstrom and it would be hard to see the slant of the line. How many pixels are there per resolution element?

By looking at the picture, can you see directly that a doppler shift have taken place? I don't get why the reference line is unusually bright

By looking at the picture, can you see directly that a doppler shift have taken place? I don't get why the reference line is unusually bright

No, I can't, that's what I was saying. Do you happen to know the identity of the central line? I can't comment without knowing that. By the way, http://www.astro.columbia.edu/~archung/research/CRdisk/Images/example.jpg an example of a line twisted by rotation (this time with the spectrum in the vertical direction).

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ok here is the full spectrum in the near IR range. It's some odd lines on the left hand side, do you happen to see any doppler shift?

If i understand correctly, this is sunlight reflected off Jupiter, which means that if there is ant shift, it should be relative to the solar spectrum?

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ok here is the full spectrum in the near IR range. It's some odd lines on the left hand side, do you happen to see any doppler shift?

No, but I still can't tell the wavelength range.

If i understand correctly, this is sunlight reflected off Jupiter, which means that if there is ant shift, it should be relative to the solar spectrum?

Some of the near-IR light would be emitted from Jupiter, but most of what you're seeing is reflected, that's right. Some of the absorption may also be from Jupiter's atmosphere.

## 1. How can we interpret spectra to determine Jupiter's rotational speed?

The rotational speed of a planet can be determined by analyzing the Doppler shift in the spectral lines of its atmosphere. As Jupiter rotates, the gases in its atmosphere are either moving towards or away from Earth, causing a shift in the wavelengths of the spectral lines. By measuring this shift, scientists can calculate Jupiter's rotational speed.

## 2. What type of spectroscopy is used to study Jupiter's rotation?

The most commonly used spectroscopy technique for studying Jupiter's rotation is infrared spectroscopy. This allows for the detection of thermal radiation emitted by the planet, which can then be used to analyze its rotational speed.

## 3. What factors can affect the accuracy of interpreting spectra for Jupiter's rotational speed?

There are several factors that can impact the accuracy of interpreting spectra for Jupiter's rotational speed. These include the instrument used to collect the spectral data, the atmospheric conditions on Jupiter, and the angle at which the planet is observed from Earth.

## 4. Can interpreting spectra also provide information about Jupiter's atmosphere?

Yes, interpreting spectra can also provide valuable information about the composition and temperature of Jupiter's atmosphere. By analyzing the intensity and shape of spectral lines, scientists can determine the presence of certain molecules and the temperature at different layers of the atmosphere.

## 5. Has the rotational speed of Jupiter been consistent over time?

No, the rotational speed of Jupiter has been found to vary slightly over time due to changes in its atmosphere and gravitational interactions with its moons. However, these changes are relatively small and do not significantly impact our overall understanding of Jupiter's rotational speed.

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