# Tag Info

Accepted

### Can we estimate the orbital period of the planet Phaeton (destroyed planet between Mars and Jupiter)?

Whether we know or believe Phaeton exited, we can estimate its orbital period from some reasonable assumptions using Kepler's third law. Kepler's third law states: The ratio of the square of an ...
• 2,339
Accepted

### Is it possible to explain the difference between synodic month and sidereal month by degrees?

A better diagram is something like this: Day 0. The Moon is aligned with the Sun (New Moon) and some star X behind the Sun (of course :-), as shown by the arrow at 1. (Neither the Sun nor the star ...
• 8,032

### How many degrees does the sidereal month orbit?

The Moon does move 3.1° in the 0.23 day difference between those month lengths, but it goes 360° in a sidereal month and 363.1° in an anomalistic month. The anomalistic month, from ...
• 18.7k
Accepted

### Right ascension and sidereal time difference

Question 1: How do sidereal time and RA correlate together? Think of the sky as a globe. The constellations and lines of right ascension (RA) are painted on the globe. Because of the Earth's rotation,...
• 8,032
Accepted

### Is the difference in time between the sideral and synodyc month - constant?

The time difference (synodic month) - (sidereal month) will not be constant. The reason for the variation is due to the eccentricity of the Moon's orbit: the Moon moves faster at perigee (closest to ...
• 8,032

### defining the period of an year on earth

Even the first item (defining what a "day" is) is not as obvious as would appear. Using sunrise to sunrise (or equivalently, using sunset to sunset) is just about the worst option, for ...
• 34.1k
Accepted

### Doesn't Gregorian Calendar being started each year on 00:00 cause a huge error in the future?

The Gregorian calendar is designed to approximate the average tropical year, that is the average length of time from one spring equinox to the next. The actual average length of a tropical year is 365....
• 123k

### Can we estimate the orbital period of the planet Phaeton (destroyed planet between Mars and Jupiter)?

The Titus-Bode law predicts1 a semimajor axis of 2.7 AU which gives it a period of 4.4 years. $$a = \frac{4 + 3 \times 2^n}{10} \ \ \text{AU}$$ where $$n = -\infty, 0, 1, 2, 3...$$ Earth with $n=1$ is ...
• 30.7k
Accepted

### Sidereal time of rising and setting of the sun on the arctic circle

You need to intepret the question a bit. By "June 22" they probably mean "Summer Solstice", likewise for "Dec 22". At the solstice the right ascension of the sun is 6hr/...
• 123k
Accepted

### The orbital period of Jupiter and Europa billions of years later

When the Sun becomes a red giant there will be some mass loss, making Jupiter's orbit wider and slower. The extent is fairly small during the initial expansion, but about 50% of the mass at the end. ...
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### What causes the variation in the length of the synodic month, BESIDES the eccentricity of the Moon's orbit? And how much do they contribute?

Q: What causes the variation in the length of the synodic month (besides the moon's orbital eccentricity), and how much do the other causes contribute? (Also) Is it true that the length of the ...
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### What causes the variation in the length of the synodic month, BESIDES the eccentricity of the Moon's orbit? And how much do they contribute?

The Moon's orbit around the Earth is not a simple Kepler ellipse. It's dynamically distorted by tidal forces, primarily from the Sun. Newton showed that Kepler's 3 laws arise from the inverse square ...
• 14.9k
Accepted

### What is precision of planet periods data?

The planetary orbits can not strictly be described by the usual Kepler elements anymore as they are disturbed by the other planets (Saturn in particular will for instance be heavily affected by ...
• 3,494

### How long is a mean Jovian tropical year in Jovian solar days?

A quick search on Google brings us to https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html where it is mentioned that Jupiterâ€™s tropical year lasts 4,330.595 Earth days and that the length ...
• 7,502

### Is it possible to explain the difference between synodic month and sidereal month by degrees?

The new moon is when the center of the Moon and the center of the Sun are at the same ecliptic longitude. The angular diameters of the Sun and Moon are not considered. Angular speeds give us another ...
• 18.7k
Accepted

### defining the period of an year on earth

One takes a reference point and simply observes repeatedly and carefully - and counts day to the next solistice, thus when the sun is again at the exact same place in the sky. That method is believed ...
• 19.7k
1 vote
Accepted

### What is the duration of a year on the Moon (Tropical/Sidereal period) for orbit about the Sun ? How/why does length of lunar days vary ? Soltices?

A day on the moon lasts 29.53 days (a synodic month), slowing down by 0.005 seconds every century. ref. The tilt of 1.54' relative to the Sun has an 18.5996 years periodicity. ref.
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1 vote

### How long was a lunar month in ancient times?

'Day' is the worst possible unit to measure the revolution of the Moon around Earth as it is the temporal unit which is directly influenced by the tidal friction and deceleration. We can reasonably ...
• 19.7k

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