15
votes
Accepted
Why does Callisto only have eclipses every 3 years?
They do happen at certain points of every Jovian year.
Jupiter's orbital period is approximately 12 Earth Years. the relative angle between the plane of Callisto's orbit and the plane of Jupiter's ...
- 4,695
12
votes
Accepted
Could there be an eclipse tomorrow if the Pleiades is covered by the Moon tonight?
Consider how far the pleiades are above the ecliptic, and how far the moon travels in a day. From this you can work the angle at which the moon must travel relative to the ecliptic, in order to cross ...
- 4,304
10
votes
Why aren't there eclipses every month when the moon's orbit is aligned with the ecliptic as a result of lunar precession?
There are few things here I think might be worth to state:
The tilt of Earth is of no importance here. As the comment says what is of importance how much the Moon orbit is inclined to the ecliptic. ...
- 1,667
10
votes
Do all the planets travel along the same constellations?
The path of the sun would be very similar.
The positions of the stars are almost exactly the same. They are so far away that moving to Jupiter won't change their apparent position in any way that you ...
- 116k
9
votes
Accepted
Why aren't there eclipses every month when the moon's orbit is aligned with the ecliptic as a result of lunar precession?
The precession of the moon's orbital plane does not align it with the ecliptic plane. The angle between those two planes is approximately 5.14° (it varies by ~±0.15°, mostly due to perturbation by the ...
- 13.1k
8
votes
Why is the equinoxes only 2 days and not more?
First, don't think that equinox is when the day and night are the same. It is the moment, when the sun's declination is zero, or when the sun is directly over the equator. Let me explain ...
Earth is ...
- 2,879
8
votes
Accepted
How to find the local azimuth of the highest point of the ecliptic
Edit:
Getting the exact value winds up being simple, but it was only later in the day that the answer occurred to me. All we need to do is ask for the altitude and azimuth of the Ecliptic’s south pole!...
- 960
7
votes
Is the equinox Sun always at the same zodiac sign in the ecliptic belt?
As you said, the Sun takes a year to cycle the Zodiac, and it takes a year between two spring or autumn equinoxes. Both statements are true, but "year" in them means two different things. It takes a ...
- 1,720
7
votes
Accepted
How does the earth's plane of orbit (ecliptic) vary over time?
The position of the ecliptic does change, due to perturbation of other planets, but only very slowly.
The invariant plane is the plane of angular momentum of the whole solar system. This is dominated ...
- 116k
7
votes
Accepted
Questions on apparent motion of superior planets
The planets do not orbit in the same plane as the Earth, they are inclined by a few degrees. This means that as they orbit the sun, they are sometimes above the plane of the Earth's orbit and ...
- 116k
7
votes
How did the ancients know the constellation in which the sun is located?
They made star maps. They mapped the posiitons of stars on the imaginary celestial sphere - whch they thought was an actual physical hollow sphere surrounding the Earth at some distance.
Because the ...
- 7,439
7
votes
Would an accumulation of dust in a planet's L1 Lagrange point plausibly obscure it from Earth?
No.
The L1 point is unstable and dust doesn't accumulate there.
A dust cloud could not be large and dense enough to obscure a planet without being so massive that it would contract under its own ...
- 116k
7
votes
Why does the moon move within the zodiacal circle if its orbit is at an angle to the plane of the ecliptic?
The Zodiac isn't a circle, it's a band centred on the ecliptic. Traditionally, it extends ~8° north and south of the ecliptic. The inclination of the Moon's orbit is ~5.145°, so it's always within the ...
- 13.1k
6
votes
Accepted
How did the Ancients understand the ecliptic using the Ptolemaic system
The ecliptic was understood to be the path of the sun relative to the sky.
Ptolemy believed the sky rotated daily around the Earth. All the planets, including the Moon and the Sun, shared in this ...
- 116k
6
votes
Accepted
Why do some solar eclipses' umbra cross arctic/antarctic regions?
I wanted to ask this question even though I realized the correct geometry in the middle of typing it. So I will answer this myself.
First of all, the sub-lunar point never exceeds 28.545 N/S. If you'...
- 1,940
6
votes
Why does moon's highest altitude change during the year
The moon's orbit around the Earth is inclined at about 5° to the ecliptic
So as the Earth progresses in its own orbit around the sun, the moon's altitude also changes
During summers the part of the ...
- 381
6
votes
Accepted
Why is there free magnesium in the ecliptic (if there is) and why would some be orbiting within the ecliptic plane but retrograde?
Mg I does indeed mean neutral magnesium atoms, but May and his collaborators weren't observing magnesium atoms orbiting in the inner Solar System -- they were seeing absorption by magnesium atoms in ...
- 16.4k
5
votes
Why is the equinoxes only 2 days and not more?
The easiest graph to consider is the graph of day-length. If the day-length varies from 8 to 16 hours, there can only be two equinoxes:
At the time of equinox, the day length changes at the fastest ...
- 51
5
votes
Why is the equinoxes only 2 days and not more?
Two further points to make are that:
(1) because of the way we define sunrise and sunset as being when the entire Sun is below the horizon not just the centre of the Sun.
(2) When the Sun is close ...
- 139
5
votes
Accepted
Galaxy plane and Earth's orbit. Connection to seasons?
I think you are asking whether there are any consequences for the Earth of the Sun and Solar System crossing the galactic plane$^1$? Yes, there have been a number of studies suggesting that their ...
- 146k
4
votes
What is meant by sun's path through zodiac
The stars are not visible during the day, but they are still there (we just can't see them because of the brightness of the sun). We can't see the stars, but we can calculate where they would be if we ...
- 116k
4
votes
What does Ptolemy mean by "a line drawn from the centre of the earth through the centre of the moon to a point on the ecliptic"
In his model, Ptolemy considered the ecliptic to be the path of the Sun—hence, a distinct circle than the path of the Moon. In modern terms, one could say that Ptolemy thus (rightly) considered the ...
- 6,701
4
votes
Accepted
Oscillation in tilt of the solar system
The tidal field of the Galaxy does lead to the oscillation of the plane of very wide binaries. The mechanism of this oscillation is identical to the Kozai-Lidov mechanism (the only difference is that ...
- 1,078
4
votes
Accepted
How to get the axial tilt vector(x,y,z) relative to ecliptic
Earth is a special case since the equatorial and ecliptic coordinate systems are defined in terms of its own rotation and orbit.
Earth's north pole vector in
equatorial coordinates is
$$\vec N_{\oplus,...
- 18.2k
4
votes
Why does the Sun track out a seemingly sinusoidal path on the celestial sphere?
Both the equator and the ecliptic are great circles on the celestial sphere.
The appearance of each on a map depends on the map projection.
In an equirectangular projection centered on the equator, ...
- 18.2k
4
votes
Orientation of local star map
By inspection of a star charting app, I'd say the circles lie in the celestial equator, ie declination equal 0 degrees. Stars above the circles are to the north and vice versa.
- 4,304
4
votes
Which way does the Earth tilt?
The equator (Earth's rotation plane) and ecliptic (Earth's solar orbit plane) cross at the vernal equinox ♈, the zero point of both right ascension and ecliptic longitude.
Relative to the ecliptic, ...
- 18.2k
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