# Tag Info

35

As @Donald.McLean said in comments, the answer is yes, the Moon can and does occult the other planets in the Solar System. When something apparently big (like the Moon) passes in front of something apparently small (another planet) it's called an occultation. (I say apparently because from our perspective the Moon appears larger than the planets.) The ...

34

Venus has a strong ionosphere that protects it against violent solar winds. So, even though Venus has no intrisic magnetic field, it has an effective, induced magnetic field due to the interaction between the solar winds and the atmosphere, that protects it against solar winds. Venus atmosphere is thick enough to have a consequent ionosphere, that would be ...

31

How was the mass of Venus measured for the first time? In the mid 19th century, Urbain Le Verrier's predicted of the existence of a then unknown planet beyond the orbit of Uranus. He even predicted this planet's orbit. The discovery of Neptune based on his predictions was perhaps his greatest accomplishment. Le Verrier then went on to investigate Mercury. ...

26

@BMF's comment links to (Gold & Soter 1969) Icarus 11, (3), November 1969, pp 356-366 Atmospheric tides and the resonant rotation of Venus. Since it is paywalled I'll add a short summary: From the abstract: The observed spin-orbit resonance of Venus, whereby the same side of Venus faces the Earth at each inferior conjunction, cannot be explained ...

20

There is an interesting article on the magnetosphere of Venus on the ESA Science and Technology site. You can find the article here and it will probably answer your question. The article states, like you did, that some planets, like Earth, Mercury, Jupiter and Saturn, have magnetic fields internally induced by their iron core. These magnetic fields shield ...

19

There seem to be a few, and none are accepted by the whole scientific community. The main ones: Venus was struck by a large body during its early formation The spin axis flipped, as can happen with a gyroscope The spin slowed to a standstill and then reversed, caused by the sun's gravity, the dense atmosphere and friction between core and mantle That final ...

16

The mass of Venus was determined by weighing the Earth, or more precisely, by determining the ratio of the density of the Earth to the density of Schiehallion, and assuming Schiehallion to be typical rock of 2500 kg per cubic meter. Prior to that, Jérôme Lalande had worked out the relative masses of the major bodies of the Solar System as a byproduct of ...

14

The strength of the Earth's gravitational field compared to the Moon and the Sun is not enough to capture and hold satellites - there are too many disruptive forces that would rip them away over time. However there are some objects at the Lagrangian points - the points where the gravitational fields of the Earth and other objects are equal and so it is ...

14

This is a very interesting question. Of course, as you noted, you have simplified things quite a bit; there are other factors besides temperature that affect habitability. Regarding Venus, you probably know that Venus is extremely hot at its surface not just because it is closer to the Sun, but because it has a thick CO2 atmosphere and is warmed by the ...

13

Yes, such events are called occultations. The Moon can occult anything within about 5 degrees of the ecliptic. The visibility of any lunar occultation is limited to a path as wide as the Moon is. This EarthSky article discusses a series of lunar occultations of planets in September 2017, including Venus as seen from Australia. The article includes a photo ...

13

This is a fun little problem that's remarkably close and the math is pretty easy when you use the right periods. Venus' synodic period, relative to Earth, is 583.92 days on average. He uses 584, but lets strive for accuracy. Venus' solar day is 116.75 days, so 5 solar days is 583.75 days - Venus does 5 rotations in nearly the same amount of time that ...

11

This is supplementary to antispinward's excellent answer and provides additional sources and a visualization from the JAXA spacecraft Atasuki. It has been shamelessly borrowed from Would it be possible to "ride the wave" on Venus? The recently published paper in Nature Geoscience Atmospheric mountain wave generation on Venus and its influence on the solid ...

10

As others have calculated, there are no predicted double transits. Since Venus transits for about 12 hours each hundred years (roughly), Venus is in transit for about 1/100000 of the time. Thus there is a (roughly) 1 in 100000 chance that a randomly chosen transit of mercury will coincide with a transit of Venus. Since Transits of Mercury occur every 10 ...

10

Either or neither. It's impossible to tell from the present. If runaway climate change occurs, then yes, the conditions on Venus could be a potential analogue for the kind of environment on Earth due to the greenhouse effect. Mars's atmosphere is assumed to have been much thicker in the past, otherwise it could not have sustained liquid water on the ...

10

If you are asking about short-term effects related to human's effect on the climate, the answer is (obviously) unclear. But in the very long term, Earth is likely to evolve to a more Venus-like state. Over the next billion years or so, the Sun's luminosity will slowly increase, which will heat Earth's surface. As a result, more water vapor will evaporate ...

10

Before we begin: how far a planet is seen from the Sun is called elongation, and it's measured in degrees. 0° elongation means it's right on top of the Sun (or behind); 180° elongation means it's opposite to the Sun (it's highest in the sky at midnight, when the Sun is on the other side of the Earth). https://en.wikipedia.org/wiki/Elongation_(astronomy) ...

10

It has a low eccentricity, but there may not be a particular reason. Image by Kheider on wikipeda using Gravity Simulator by Trevor Dunn In a simulation of the solar system, both Earth and Venus had orbital eccentricities that were much below those of Mars and Mercury (note the two axes. Mars and Mercury are on a scale that is 10 times bigger). But in ...

10

You're correct; extraterrestrial phosphine is not actually a new discovery. As you said, we've known for decades (see e.g. Ridgway et al. 1976) that phosphine can and does exist in some gas giant atmospheres, including Jupiter's. However, detailed modeling has been done of the associated photochemistry beginning at around the same time, and as far as I'm ...

9

There are other ways to lose atmosphere. For example Jean's Escape. If average velocity of a gas molecule exceeds escape velocity, the planet will lose atmosphere. Venus' atmopshere is mostly $CO_2$ which has a higher molecular weight than the $0_2$ and $N_2$ of our atmosphere. So, for a given temperature and pressure, the carbon dioxide molecules have a ...

9

You can think of it in terms of Hohmann transfer orbits, which define the minimum $\Delta v$ that needs to be applied to bring something from one orbital radius to another orbital radius when orbiting a massive body. This calculation takes into account that the two objects have Keplerian orbits where the objects begins with at least the orbital speed of the ...

9

Yes, but such an event would be very rare. Venusian transits last only about 7 hours, and there are only two in 113 years, So Venus is in transit for about 0.0015% of the time. So as a back-of-the-envelope calculation, you would need to see about 70000 eclipses before you had a combined transit/eclipse. There are about 2 solar eclipses a year, so you might ...

8

It's unlikely that either Mercury or Venus could have moons to begin with. Both of these planets are pretty close to the Sun — and in general, this prevents moons from finding stable orbits. If a moon were too close to the planets, it would fall within the Roche limit and be torn apart by tidal forces. If a moon were too far from the planets, it would fall ...

8

I think you'll have to live with an incomplete answer. It appears this was taken by an amateur astronomer using a simple 4.5 inch telescope. You can find, on the ESO website, a collection of many images taken during the 2004 transit. On this page, is the image you are asking about (along with some other images by the same person). The credit for that image ...

8

Venus orbits the Sun at 0.723332 AU. As solar radiation follows an inverse square law, the intensity of the Sun at the top of Venus's atmosphere is almost twice that for the Earth ($\frac1{0.723332}^2\approx1.9113$). Even when the solar system was young and the Sun was considerably dimmer than it is now, Venus received 1/3 more solar radiation at the top of ...

8

Essentially what they did was assume that normally when observing with their telescope the spectral absorptions they see are due to the Earth's atmosphere. Which is a pretty good assumption. They then normalize the data to those absorption, so if there was any phosphine gas within the package of atmosphere they are looking through, it will be taken into ...

8

This web page -- "Here is why the Hubble Space Telescope only looked a few times at Venus (and why it looked at the Moon instead)" -- seems like a pretty good answer to your main question (note: "MAST" = Mukulski Archive for Space Telescopes): There are only a few times the Hubble Space Telescope did look to Venus according to MAST. ...

7

My ad-hoc opinion: This wouldn't be the first step of Venus exploration. Geologic in-situ investigation of the resurfacing hypotheses would already be a very challenging mission. Might be, one could find some metamorphic remnants which have survived the last resurfacing, and one could determine the age of rocks. Might be there exist some old layers below the ...

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