Why does the Sun have different day lengths, but not the gas giants?
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The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.
Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.
the-sun rotation gas-giants
asked 2 hours ago
AllureAllure
42519
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add a comment |
$begingroup$
The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.
Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.
the-sun rotation gas-giants
asked 2 hours ago
AllureAllure
42519
$endgroup$
add a comment |
$begingroup$
The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.
Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.
the-sun rotation gas-giants
asked 2 hours ago
AllureAllure
42519
$endgroup$
The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.
Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.
the-sun rotation gas-giants
the-sun rotation gas-giants
asked 2 hours ago
AllureAllure
42519
asked 2 hours ago
AllureAllure
42519
asked 2 hours ago
AllureAllure
42519
asked 2 hours ago
AllureAllure
42519
asked 2 hours ago
AllureAllure
42519
42519
add a comment |
add a comment |
1 Answer
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$begingroup$
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)
The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.
We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.
answered 1 hour ago
MarkMark
1,639619
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1 Answer
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1 Answer
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$begingroup$
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)
The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.
We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.
answered 1 hour ago
MarkMark
1,639619
$endgroup$
add a comment |
$begingroup$
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)
The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.
We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.
answered 1 hour ago
MarkMark
1,639619
$endgroup$
add a comment |
$begingroup$
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)
The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.
We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.
answered 1 hour ago
MarkMark
1,639619
$endgroup$
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)
The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.
We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.
answered 1 hour ago
MarkMark
1,639619
answered 1 hour ago
MarkMark
1,639619
answered 1 hour ago
MarkMark
1,639619
answered 1 hour ago
MarkMark
1,639619
1,639619
add a comment |
add a comment |
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