Tagged Questions
3
votes
2answers
261 views
When is the right ascension of the mean sun 0?
I understand that the right ascension of the mean sun changes (at least over a specified period) by a constant rate, but where is it zero? I had naively assumed that it would be zero at the most ...
2
votes
1answer
98 views
The validity of the Longitude of Perihelion
As I understand it from Astronomical Algorithms, by Jean Meeus, the Longitude of Perihelion is a very common numeric value associated with planets, even used as one of the planetary orbital elements. ...
10
votes
1answer
367 views
What accounts for the discrepancies in my calculations of year lengths?
A common exercise in many introductory astronomy texts is to use the lengths of various kinds days to calculate the approximate length of the corresponding year.
For example, ratio $k$ of the length ...
2
votes
2answers
293 views
Does the length of the sidereal day vary systematically?
I'm confused about some properties of the sidereal day, in particular whether its duration varies systematically over the course of the year.1 It seems to me that that must be the case, but the ...
1
vote
1answer
112 views
What are “cycles of anomaly” and “cycles of longitude”?
In several early (pre-1600) astronomical texts I read about "cycles of anomaly" and "cycles of longitude", but it us unclear to me what these terms mean. They were clearly familiar to authors at the ...
1
vote
0answers
116 views
What is the angular distance between Ptolemaic perigees of Mercury?
In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that
The complicated [Ptolemaic] model of Mercury has the curious ...
3
votes
1answer
233 views
When and how were relative distances to the planets first measured?
I understand that the absolute distance to a planet can be measured using earth-baseline (e.g., diurnal) parallax, and that the first reasonably accurate such measurement was made for Mars by Cassini ...
8
votes
2answers
269 views
Was Jupiter's mass “guessed at” by Kepler or Galileo?
Following Kepler's publication of his 3rd law of planetary motion1,
$$p^2 / r^3 = 1$$
in 1619, it would have been possible to use telescopic observations to arrive at an estimate of the orbital ...
6
votes
1answer
562 views
What happened to Apollo's Saturn-third-stage rockets?
I read recently the original Apollo 11 press release and it mentions that the Saturn V's third stage (used for Trans-Lunar Injection) was deployed into a solar orbit of some kind:
I know that on ...
1
vote
2answers
110 views
Will Pluto be in the ecliptic plane when New Horizons passes by? Was this deliberate?
From the illustrations at the New Horizons website it seems that Pluto may be in or near the ecliptic plane when New Horizons passes by.
Is this intentional? Of course Pluto was to move to that ...
3
votes
2answers
104 views
Cannon on spacecraft: hitting yourself
Some Soviet space stations reportedly had anti-aircraft cannons installed. Could such a cannon hit the firing space station accidentally on a subsequent orbit? The muzzle velocity of the cannon is ...
2
votes
1answer
58 views
Sunrise time across the globe?
This question is more astronomy related, I started thinking when I heard from one of my friends living in Jiamusi, that Sun rise at 02:00 and sets at 14:00, I know that this place is more near to ...
5
votes
1answer
364 views
Might a planet perform figure-8 orbits around two stars?
Might a planet perform figure-8 orbits around two stars?
I'm thinking that if the two stars were equal mass (and not orbiting each other) then a planet that were to go right between them would ...
1
vote
1answer
71 views
What's the amount of deviation of cellestial orbits from perfect ellipses
It's well known that the planets don't orbit the sun in perfect circles and the characteristics of the elliptical orbits which serve as better approximations to their motion have been calculated ...
1
vote
0answers
230 views
How to find orbital radius of star in a binary system using redshift and orbital period data? [duplicate]
Possible Duplicate:
About binary stars and calculating velocity, period and radius of their orbit
I am given the non-redshifted wavelength of the EM radiation from one of the stars, the ...
0
votes
2answers
81 views
On constancy of cometary orbits
how are the comets able to keep to a nearly fixed orbital period, though they lose a certain amount of mass during their perihelion?
4
votes
2answers
342 views
What's the reason for the seasons?
In the diagram, it shows that the fundamental reason for different seasons is when the northern hemisphere is titled towards the sun there's summer in northern hemisphere and winter in southern ...
1
vote
3answers
101 views
Rocket needed to send 100 gram of mass to outer space? [closed]
What kind of rocket would be needed to send 100 gr of mass to outer space?
The mass can be moulded in any shape, but it would need not raise above 40 °C of temperature during the ...
3
votes
1answer
367 views
About binary stars and calculating velocity, period and radius of their orbit
I saw somewhere about being able to measure the velocity, period and radius of a binary star orbit by looking at red shift and blue shift.
I understand it but can someone give me an example of ...
0
votes
1answer
110 views
How to find the orbit of a moving point object given 3 past passing positions?
How do I find the orbit of a moving point object given 3 past passing positions and the tangents at these passing positions, and given that the orbit is known to be an ellipse?
0
votes
0answers
106 views
How long until “final totality”? [closed]
It is given that the angular size of the Sun as viewed from Earth is $0.533^\circ$, the distance of the Moon from Earth at perigee is $3.633\times 10^5$ km, and the mean radius of the Moon is $1737.1$ ...
12
votes
1answer
88 views
Why don't stars in globular clusters all orbit in the same plane?
Globular clusters like Omega Centauri certainly don't seem to be very coplanar at all.
In other words, why doesn't the explanation at Why are our planets in the solar system all on the same ...
6
votes
3answers
169 views
“Reverse engineering” of a horoscope?
I'll start with a disclaimer -- this is not a question about astrology itself, I'm neither trying to refute nor to defend astrology. I'm interested in purely technical things, which are mostly ...
3
votes
2answers
44 views
Computing period, semi-major axis of binary
I have mass, $g$, and luminosity of each of the stars in a binary system, extracted from a model. I calculated the individual radii from $g$ and the mass. I am trying to compute $a$, but I seem to be ...
4
votes
1answer
350 views
How does the view of night sky change as the Sun orbits around the Milky Way?
I know that the Sun and hence the Solar System orbits around the galactic center of the Milky Way. Does this rotation cause any visible change in the night sky?
I know that human life span is ...
6
votes
3answers
1k views
What is the irregularity in Uranus' orbit that is caused by Neptune?
I carefully read the Wikipedia article Discovery of Neptune, and I don't get what the irregularity of Uranus orbit was that lead to the discovery of Neptune. Years ago, I watched some educational film ...
3
votes
1answer
37 views
Do stars of higher metallicity have more planets in highly-inclined Pluto-like orbits?
In an answer to a previous question of mine, one that asked about the planar orbits of inner planets, I was told the following (emphasis mine):
On the subject of different solar systems, I would ...
7
votes
1answer
13 views
What tools do I need to track an orbit of a mystery object?
A while back I was observing Uranus with my 6" dob and a moving object tracked across my field of view. I was at about 90x at the time, and the object was pretty bright but slow moving. I dropped down ...
6
votes
2answers
216 views
Are there planetary systems where the planes of orbits vary greatly?
Inspired by this question, are there any known planetary systems with largely varying planes of orbit? For example a system where two planets have perpendicular planes?
3
votes
1answer
776 views
Find true anomaly given period, eccentricity and time
Is it possible to find the true anomaly of an object in a Kepler orbit given the orbital period of the object, the orbital eccentricity and the time? Assuming a two body system and the mass of the ...
6
votes
3answers
252 views
How accurately is the moment of perihelion of Earth known, and how is it measured?
Earth's perihelion passed about nine hours ago. How accurately do we know the moment of closest approach of the Earth to the center of the sun? How do we make this measurement?
9
votes
6answers
2k views
Why are the orbits of planets in the Solar System nearly circular?
Except for Mercury, the planets in the Solar System have very small eccentricities.
Is this property special to the Solar System? Wikipedia states:
Most exoplanets with orbital periods of 20 ...
