# Tag Info

53

There are two forces that can cause the formation of a tail: the solar wind and radiation pressure. The first misconception in your question is "the dust [travels] slower than the nucleus". The tail is not left trailing behind the comet, it is pushed away from the comet by the sun. When the comet is moving away from the sun, the tail is in front of the ...

42

No. Besides the 13 Jupiter-masses required to ignite deuterium burning, and make Jupiter into a Brown Dwarf, there is a clear difference between the formation pathways of Brown Dwarves and Gas Giants. Gas Giants are planets, that form via processes in their parent protoplanetary disc. Contrasting this, Brown Dwarves form via direct fragmentaion of the ...

41

The sun is the nearest star to Alpha Centauri (unless you count Proxima Centauri, which is really part of the same system). There is a very small and dim pair of brown dwarfs, called Luhman 16 that are closer, at about 3.6 light years from Alpha Centauri. Brown dwarfs are not true stars, but they do glow from their own heat. They were only discovered in ...

35

First, there is not just one tail, it is several, but when traveling far from a star, they are "aligned". When it gets closer the different materials behave differently, both depending on the temperature they start to vaporise and how they are affected by solar winds. I think this picture shows it in a good way. https://community.dur.ac.uk/physics....

29

The outer parts of Neptune are mostly hydrogen and helium. There are small amounts of other gases such as methane, ammonia and water vapour. However, there is no oxygen at all. If you took some of Neptune's outer layer back to earth and mixed it with our air, it could burn. Even very cold hydrogen can burn (it soon heats up!) This couldn't happen on ...

18

If the Sun had been born in a relatively wide binary system with a star that was to become a black hole or neutron star via a supernova, then (a) it is quite likely that such a system would be disrupted by that supernova and we would not be in a binary system now; (b) there should be evidence of the supernova in the form of very high abundances of the ...

16

Short answer: no It all of course depends on how you define the term failed star. In general, a star should be able to generate heat by fusing atoms together, and it requires about 13 times the mass of Jupiter for conditions to be adequate for sustained deuterium fusion, and about 63 times the mass of Jupiter for fusion of lithium to take place. All other ...

16

It's certainly possible for a star system to be stripped away if its galaxy interacts gravitationally with a second galaxy. Tidal forces between the two can disrupt stellar orbits and form tidal tails and other possibly transient structures. This won't happen on human timescales - no satellite galaxies are anywhere close enough to us to pose a threat - but ...

16

No, although there are times when it can't be seen, it isn't true that it is visible for 183 days of the year. The general question could be "If I take an arbitrary location on the sky (say a randomly chosen star) will it be visible for half the year? The answer is "it depends on the star!" Polaris and many other stars are circumpolar for ...

13

The time of the orbit is not well known but the inclination can't change as much (small changes in velocity due to outgassing can significantly change the orbital period, but can't change the inclination much. So, while we have a good idea of it's orbital track close to perihelion, we just don't know when it will be there. We don't know where the Earth will ...

10

Since the question has sit unanswered for months, I'm trying to give an acknowledgedly incomplete answer. In summary: By 1700 it would have been a reasonable guess. By 1800 it was becoming an observed trend. TL;DR: It's hard to decide when the consensus was created on the typical orbits of satellites, because there are only a few data points (planets with ...

10

Kevin Walsh, lead author of the original Grand Tack paper has a page on his website discussing the Grand Tack model and subsequent work. At the bottom of this page there is a movie of the evolution taken from the numerical simulation that was the basis of the paper and the Grand Tack model. Sean Raymond (one of the other authors on the Walsh et al. 2011 ...

10

Light flux decreases as one over distance squared. So if Eris is 100 times further away from the Sun than the Earth is, then the amount of light that reaches Eris is 10 000 less than that on Earth. Since a difference of five magnitudes is a factor of 100, The Sun would have an apparent magnitude -16.7 seen from Eris' aphelion, as opposed to -26.7 magnitude ...

10

Well if no one is going to answer this I will. The answer is we don't know for sure. We speculate that there should be earth rocks on mars but until we 'see' one and analyze it we will not know for sure. The comments here all point to this answer. Mars hit with thousands of Earth rocks possibly containing life following asteroid impacte talks about the ...

9

While the eye is terrible at determining apparent magnitude or brightness of stars due to our adaptive iris, it's perfectly capable of discerning relative brightness between two objects in the same visual field. Also, the ancient Greeks could discern six magnitudes of star brightness by realizing that brighter stars look bigger in the night sky. The word ...

9

Everything is in motion in our Galaxy. The Sun has executed some 20 laps of the Galaxy since it was born and may have migrated inwards or outwards to some extent. The Sun's location has nothing to do with the Gould belt or vice versa. The Gould belt stars formed just 30 million years or so ago. The position of the Sun relative to the Gould belt is a ...

9

Short answer Short answer is no, it can't prove or disprove the existence of Planet 9. The reason is because, even if there is a significant difference between the barycenter of the solar system with and without Planet 9 we wouldn't be able to tell without hundreds if not thousands of years of precise data. If we don't have Planet 9 as a reference and are ...

9

It is important to appreciate the scale of the comet's orbit compared to the Earth's orbit. The Earth goes round the Sun in a nearly circular path. The average distance is one Astronomical Unit (AU). C/2020 F3 (Neowise) has an incredibly skinny elliptical orbit. It's closest approach to the Sun (perihelion) is at 0.3 AU, which is inside the orbit of Mercury. ...

8

Turner's expression for the radius of curvature ρ is correct, but in case (3), ρ = -0.988 a where the Moon is in the first or last quarter (θ = 7.5° or 22.5°). Where the Moon is full (θ = 15°), ρ should be -0.749 a. Case (1) models a spacecraft stationed at L1 (b = a / 100, ρ = -0.99 a) or L2 (b = -a / 100, ρ = -1....

7

We don't really know what the statistics are for the frequency of solar systems is as a function of stellar density and many such systems in dense regions may be disrupted by close encounters with another star. What I surmise you want is an estimate of the density of stars as a function of Galactocentric radius. In the solar neighbourhood, there are 378 ...

7

I'll touch on a few of these because I disagree with some of those ideas. There are approx. 2000 planetary systems discovered, and all of them, except the Solar System, have angular momentum mostly in a star There's a few problems with that argument because planets close to their star are easier to identify. We don't have a complete picture of the ...

6

The cometary particles need not retain the exact same orbit as the comet in order to stay close together near perihelion, thus where their orbit passes Earth's orbit. Slight changes in the orbital parameters of the released dust particles can include slighly higher or lower aphelion, and thus change the revolution time and the time of perihelion (Earth) ...

6

To simplify, I used Starry Night to generate a visualization. The yellow arc is a piece of the ecliptic. You can see (in faint gray) the center of the yellow arc is labeled 'Dec'. The Sun will be in this part of the sky in December. You can also see planets of the inner solar system and in the background, part of Sagittarius (and the Teapot asterism) is ...

6

Simply because we can see the sun. The comet will be swinging around the sun, getting closer to it than the Earth does by a large factor. This path cannot always be in-line with the sun or other body orbiting the Earth or the Sun, so there isn't a way for our view to be blocked. It is plausible that its approach could be mostly co-linear with the sun, or ...

5

According to Wiktorowicz & Ingersoll (2006), Neptune is too hot and too dry to form liquid oceans at the present time. This may seem counterintuitive for a planet with a far higher bulk fraction of water than the Earth which is located so far from the Sun, but the water is going to be mixed up with hydrogen, helium and various other materials in the ...

5

I would say that the only way this can be done is making ever more careful observations of the TNOs that are claimed to be affected by this putative black hole. Ultimately such observations should narrow down the location of the object. Even then, confirming it's existence will be very difficult. It will have a small lensing/magnification effect on ...

5

Mercury's orbit is highly eccentric: 0.21 according to Wikipedia. Therefore, the actual time between repeating occurrences will vary depending on the year. If you were to perform your calculations for many periods, the average should approach the value given by Stellarium. The theoretical synodic period, using the sidereal period of Earth and Mercury, is ...

5

Let us first consider the Earth a fixed point and Mars moving around the Sun on a circular orbit with angular velocity equal to the relative angular velocity ($\omega_\bigoplus - \omega_♂)$ The distance between Mars and the Earth can be described as the square root of $R_E^2+R_M^2-2R_ER_Mcos(\theta)$, and when this is equal to $R_E^2$: \$cos(\theta) = \frac{...

5

You wouldn't need to travel too far, the moon has been bombarded with large amounts of Helium3. https://www.esa.int/Enabling_Support/Preparing_for_the_Future/Space_for_Earth/Energy/Helium-3_mining_on_the_lunar_surface

5

Moon Even though the Moon obviously isn't a planet, it's a good place to start as most of the observations of meteorites hitting other bodies has been focussed on the Moon. NASA runs the Meteoroid Environment Office which in part monitors lunar impacts. They state; The lunar impact rate is very uncertain because observations for objects in this mass range ...

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