Astronomy

Closest point on Earth to a planet?

Closest point on Earth to a planet?


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I'd like to be able to find the latitude and longitude on Earth (assuming a sphere is fine) which is closest to Pluto at the current time (or where Pluto is directly overhead).

Is this possible with PyEphem?


#!/usr/bin/python import ephem, math obs = ephem.Observer(); obs.long,obs.lat=0,0; pl = ephem.Pluto(ephem.now()) print 180.*(pl.g_ra-obs.sidereal_time())/math.pi,180.*pl.g_dec/math.pi

To a good approximation, the code above will tell you the longitude and latitude (in that order) where Pluto is currently overhead. You can edit it for different planets/times.


Your question is valid and is a common operation. When computing when an object will be visible, many observers want to be able to draw a globe or map that is marked with the position from which an object like Pluto is directly overhead. Such a position on the globe at a given instant (and you do say “at the current time”) is, all other things being equal, the best-situated place from which to observe the object.

Unfortunately, the “libastro” C library that PyEphem wraps seems to only provide one instance of this concept: Earth satellites have.sublatand.sublongattributes, because it is so common to want to draw the path of a satellite on a globe or map.

But libastro does not generalize the concept. From what I can see, there is no way to generate the point on the Earth that is directly below any other Solar System object. And since I have not been in the habit of trying to extend libastro, it is likely that PyEphem will not gain this ability.

However, I have been developing a replacement for PyEphem that is written in pure Python and that I will be free to extend, called Skyfield. I will hopefully have this concept working there soon, and when I do so I plan to make it work for all objects, and not limit it to Earth satellites!

(In the meantime, as pointed out in the comments: you could try asking PyEphem for the geocentric RA and dec and, if you could adjust RA by the Earth's current hour angle, then you could turn those into an approximate latitude and longitude.)


The orbital speed of Earth around the Sun is 30,000 m/s, the highest mountain is about 9,000 m and the rotational speed of the surface around the polar axis is about 450 m/s. So this makes me conclude that topography such as height over the Sea has to be of little importance.

The polar axis around which the Earth turns is tilted by 23 degrees relative to the ecliptic plane of the planets' average. Pluto's orbit is 17 degrees tilted so every region on Earth between +40 and -40 degrees latitude should, sequentially in time, be the one spot on Earth's surface which is closest to Pluto. Spread out over looong times. That's about between New York and Sydney. For the least inclined planets the nearest point on Earth would be somewhere between Houston and Rio de Janeiro, i.e. every place on Earth within 24 degrees north or south of the equator (except very local depressions).


Closest point on Earth to a planet? - Astronomy

Planet Earth is the third planet closes to the sun. Using the old saying, “My Very Educated Mother Just Served Us Nine Pizzas,” it can be remembered that the order of the planets goes like this: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (if you consider it to be a planet). Accordingly, it would seem as though either Venus or Mars would be the closes planet to Earth. But which is it?

Asking which planet is the closest to Earth is actually something of a trick question – the closest planet to Earth can change depending on the day, month, or even year. Rather than stating a time frame to describe when a given planet will be closest to our own planet, it is actually most accurate to describe a position that would indicate which planet is closes to ours. Since every planet has its own orbit around the Sun, and every orbit is a different length, all planets have different periods that would signify a year (or a complete orbit of the Sun).

When Venus is in the middle of the Sun and Earth, it is at its closest point to Earth. During this period, Venus would be the closest planet to Earth. However, there are times when Mars is actually the closest planet. For example, during August 2003, Earth and Mars were at such a point in their orbits that Mars was at one of its closest distances to Earth. It was only around 35 million miles away from the planet, which may sound like a long distance but is actually close considering it can be over 200 million miles apart from the Earth depending on where each planet is in its orbit. Given this relatively close distance, Mars was actually closer to Earth than Venus was at this time.

On rare occasions, Mercury can be the closest planet. For example, over 2,000 years ago, Mercury was only around 35 million miles away from our own planet. However, occurrences like this are extremely rare and can happen thousands of years apart.


It’s Cold Outside, but Earth Is at Its Closest Approach to the Sun

Our planet’s elliptical orbit doesn’t affect winter or summer temperatures. But some astronomers wonder whether it’s a factor in why life survives.

This story was updated to reflect 2021’s perihelion.

Early on Saturday (8:50 a.m. Eastern time, to be exact), Earth made its closest approach to the sun and reached a point in its orbit known as perihelion. Chilly as winter may feel in the Northern Hemisphere, we’re more than three million miles closer to our fiery star than we were in the dead of summer.

The change in distance occurs because our planet’s orbit is stretched into an ellipse — so Earth snuggles up to the Sun every January and dips farther out into the outer solar system every July, at a point known as aphelion.

Although three million miles sounds vast, it’s not much on the scale of our solar system. In fact, despite the planet’s elliptical path through the heavens, most astronomers say that Earth’s orbit is basically circular. On a scale of 0 to 100 percent, where 0 is a perfect circle and nearly 100 is a very thin oval, Earth only scores a 1.7.

It’s a defining trait that keeps our planet at roughly the same distance from our sun, and keeps the climate relatively stable. This has led many astronomers to wonder whether a circular orbit just might be a crucial ingredient in the cocktail of life — and a key factor to consider as they search for signs of alien life around the thousands of exoplanets known to be circling other stars within the galaxy.

Consider the exoplanet known as HD 20782 b, which boasts the highest eccentricity yet discovered — a whopping 97 percent. Although the alien world is likely more akin to Jupiter than Earth in mass, it’s easy to imagine what might happen to a wildly eccentric Earthlike planet.

At its closest approach to the star, the planet would face an explosion of heat that would evaporate the planet’s oceans and strip the planet’s atmosphere, sending crucial molecules such as oxygen streaming into space. The planet itself would also undergo dramatic tides, causing it to change shape, stretched by the star’s enormous gravity, and produce violent volcanic eruptions. Later, at its farthest distance from the star, the planet would undergo a long and deep freeze.

“This incredible seesaw of extreme conditions would devastate the planet, and I expect that it would not take very long for the planet to become a desiccated, barren rock,” said Stephen Kane, an astronomer at the University of California, Riverside, who described his own research as obsessed with eccentricity.

Such a dire portrait could suggest that life prefers a circle. But do most exoplanets orbit their host stars in bands similar to the Earth, or are their orbits more like that of HD 20782 b? In 2012, Dr. Kane and his colleagues analyzed the planets detected by NASA’s Kepler space telescope and found that smaller, rocky worlds tend to reside in circular orbits, whereas large, gaseous planets do not. This suggests that most of these rocky worlds might be able to host a stable climate and, therefore, life.

But Dr. Kane and other researchers warned against dismissing the possibility of life forming on worlds with highly-eccentric orbits.

“We should be very careful not to be too quick to exclude the possibility that these planets might have life,” said Vincent Van Eylen, an astronomer at Princeton University.

In fact, several recent studies have shown that a planet’s eccentricity can be nudged fairly high before that world becomes toxic.

Last year, Dr. Kane and his colleagues estimated that a planet with an eccentricity as high as 30 or even 40 percent could remain habitable — that is, it could have a temperature that supports liquid water — even as it swings toward and away from its host star. To pull off such a trick, the planet would need to host vast oceans of water and a thick atmosphere. Because water takes much longer to heat up and cool down than one might expect, the planet could avoid overheating in the summer and freezing in the winter. Likewise, a thick atmosphere would help keep a planet cool when it’s close to its host star, and serve as a blanket when it’s far away.

But there’s a limit to the amount of mayhem that these oceans and atmospheres can absorb.

While Dr. Kane says that an eccentricity of 30 to 40 percent is the upper limit, Sean Raymond, an astronomer at the University of Bordeaux in France, has argued that even a planet with near 60 percent eccentricity might be able to support life. Above this boundary, planets will have climates like that of HD 20782 b — one that gets thrown from the deep fryer to the freezer and back again.

But even then, the galaxy and its many orbiting planets could surprise us. “I think it’s often assumed that life is wimpy and needs ‘just so’ conditions to exist,” Dr. Raymond said. “But life on Earth did indeed survive some tough times.”

Roughly 650 million years ago, for instance, vast sheets of glaciers entombed our planet in a frozen skin that lingered for millions of years. It was a deep freeze, similar to what happens when these elliptical planets approach aphelion, that should have been deadly.


Chimborazo peak, Ecuador: the closest place to space on Earth

W e reached the campsite at about 2pm, a flattish expanse of gravel and boulders at about 5,100m (16,732ft) where we put up the tents. I managed to force down some instant noodles, gazing up at the summit, panting slightly from the exertion of eating. All I had to do was climb the equivalent of Ben Nevis, I told myself – though admittedly after it had been relocated to the top of Mont Blanc. I lay down in my tent, wearing all my clothes inside the sleeping bag, shivering. Outside it began to snow. I drifted into a half-sleep, disturbed only by having to make several dashes outside: my stomach was nervous too.

I’m not sure where the challenge of climbing the world’s highest mountain came from. When I was a boy I’d read about Alexander von Humboldt, that most inspiring of explorers, who in 1802 had narrowly failed to reach the summit of an Andean peak called Chimborazo. In those days, my book had informed me, Humboldt believed it to be the highest mountain on Earth. There was more than a hint of condescension in that wording, a sense of “we know better now, don’t we?”

But we don’t. Chimborazo is still the highest mountain on Earth, at least when measured from the Earth’s centre rather than sea level. Since our planet is a squashed sphere not a round one, and peaks close to the Equator get an extra few kilometres, Ecuador’s tallest peak emerges supreme, the point on Earth closest to outer space. With this method the “top 10” of mountains is rewritten: Kilimanjaro (5,895m) leaps up to seventh from well outside the top 150 highest above sea level Cayambe, Chimborazo’s near-neighbour, comes in eighth Everest and the rest of the Himalayas are nowhere and I am lying in a tent in the Andes, not Nepal.

The camp at 16,500 feet below Stubel Glacier. Photograph: Kevin Rushby

My calculations do not end there: at 6,268m Chimborazo is, I reckon, just within reach of normal human beings, both physically and financially, whereas Everest, at 8,848m, is not. It is Chimborazo that ought to be famous, its praises sung far and wide as the greatest possible challenge for that unsung hero of modern times: the amateur.

The altitude, of course, remains a problem. I had done what preparation I could at home, but more importantly spent a week acclimatising in Ecuador. I checked into the Alta Guajan homestay in a hamlet just west of Cotacachi, two hours’ drive north of Quito, and began exercising.

The early signs were not good. Eager to prove to myself that altitude was not going to be an issue, I set out at 3,000m, walking briskly to the rim of Cuicocha volcanic crater. I had just spotted two Andean condors soaring when my head started spinning and I blacked out.

Only for a minute, and I subsequently ambled around the lake without further problems, but my confidence had taken a big knock. Back at the homestay later that day, I rubbed the lump on my head and pondered: if I fainted at 3,000m, what chance for 6,000m? I found online reports of oxygen-depleted climbers being rushed down mountains and of headaches so severe that sufferers vomited uncontrollably. I was searching for excuses – and discovering that altitude provides them in abundance.

Next day I free-wheeled a bicycle down from 3,600m into the Intag Valley, passing through gorgeous cloud forests. After a visit to a coffee plantation at 1,500m, I was filled with oxygen and caffeine, enough to cycle slowly back up. A little self-confidence was restored.

Kevin and his guide, Estalin, on Cayambe, the near-neighbour to Chimborazo. Photograph: Kevin Rushby

Each day I went a little higher and further, climbing to El Voladero lakes and then Fuya-Fuya, a 4,250m mountain. Every evening I dined magnificently on my hosts’ sturdy cuisine: thick soups served with popcorn, myriad fruit juices, and tortillas made with plantain. I had everything out of their garden except the fatted guinea pigs: they were saving them for a festival day. I did everything slowly and slept a lot, but the week flew past.

When it was over, I went to Quito and met my climbing guide, a highly experienced mountaineer called Estalin. I was kitted out with rental boots, ice axe and crampons. A few adventurous souls do reach the summits without ice axe experience, Estalin told me, but most have done some training beforehand.


Not all spacecraft end up in Poin Nemo

Most spacecraft end up in Point Nemo, but there are exceptions too. For example, China’s out-of-control space station, Tiangong-1, did not crash on Point Nemo.

Tiangong-1 launched on 29 September 2011, and its operational life cycle was predicted at two years. On 21 March 2016, after its lifespan extended by two years, the Space Engineering Office of China announced that they had disabled data service since the space station had operated two and half years longer than its intended two-year service plan.

The officials went on to state that the telemetry link with Tiangong-1 had been lost. But, a couple of months later, amateur satellite trackers watching Tiangong-1 began to speculate that China’s space agency had lost control of the station. In September, after conceding they had lost control over the station, officials announced that the station would re-enter and burn up in the atmosphere in April 2018.

Artist’s illustration of China’s Tiangong-1 space station. It started reentry over the southern Pacific Ocean, northwest of Tahiti, on 2 April 2018 at 00:15 UTC and burned up in the atmosphere. It didn’t end up in Point Nemo, the spacecraft graveyard.

Harvard astrophysicist Jonathan McDowell, among others, told the British daily newspaper The Guardian that parts of the craft such as the rocket engines are probably too dense and tough to be burnt up upon re-entry and may result in chunks of debris up to 100 kg (220 lbs) in weight falling to the Earth’s surface, with little possibility of predicting where they may crash.

The 8.5-tonne spacecraft reentered the Earth’s atmosphere at approximately 00:16 UTC on 2 April 2018 over the South Pacific Ocean a 24.5 °S 151.1 °W. According to Chinese state news agency Xinhua, the station mostly burnt up upon re-entry. A fisherman from the nearby island of Maupiti was able to witness the event. It was the largest spacecraft to re-enter the atmosphere since Fobos-Grunt (see notes 2) in January 2012. This was about 3,600 kilometers (1,900 nautical miles) from Point Nemo. As the spacecraft made an uncontrolled reentry, this was an unintended coincidence.

In fact, every few years, uncontrolled spacecraft of this size enter the Earth’s atmosphere.

For example, the 5,900-kilogram (13,000 lb) NASA-operated orbital observatory Upper Atmosphere Research Satellite (UARS) decommissioned and re-entered Earth’s atmosphere on 24 September 2011. It ultimately impacted a remote area of the Pacific Ocean. Some decommissioned spacecraft have returned so remotely that there was no visual evidence of their fall.

There were uncontrolled reentries of even much larger spacecraft than Tiangong-1 in space exploration history. The biggest uncontrolled entry of a spacecraft was on February 1, 2003: the Space Shuttle Columbia disintegrated upon reentering Earth’s atmosphere, killing all seven crew members.

The 'Highest' Spot on Earth?

Due to a bulge around the equator, Ecuador's Mount Chimborazo is, in fact, closer to the moon and outer space than Mount Everest.

At 29,035 feet above sea level, Mount Everest is taller than Chimborazo, which is 20,702 feet above sea level (according to Joseph Senne). iStockPhoto.com hide caption

At 29,035 feet above sea level, Mount Everest is taller than Chimborazo, which is 20,702 feet above sea level (according to Joseph Senne).

Well, we all know that Mount Everest, at 29,035 feet above sea level, is the highest spot on our planet and is likely to remain so for a long, long time. unless we think about the word "highest" in a different way.

Suppose I asked you to find the spot on Earth where you would be closest to the moon, the stars and outer space. In other words, the point on Earth that is closest to "out there."

Most of us, again, would point to Mount Everest.

But here's something you may not know: the Earth is not a perfect sphere. (And by the way, if you want to see a really, really outrageously perfect sphere, check this out.)

The Earth Isn't Perfectly Round

The Earth, it turns out, is more like a beach ball that someone sat on: It has a slightly distended middle.

Mathematicians call this an "oblate spheroid," which means there is a bulge that circles the Earth just below the equator, so anyone standing in that part of the world is already standing "higher," or closer to outer space, than people who aren't on the bulge.

Therefore people in Ecuador, Kenya, Tanzania and Indonesia are all a bit closer to the moon (not much, only about 13 miles closer) than people standing at the North and South poles.

Let's Climb Some Equatorial Mountains

Now to make it even more interesting, suppose we climb to the top of a mountain just south of the equator. There are several famous ones: Mount Kenya in Kenya, Mount Kilimanjaro in Tanzania, and a bunch of not-so-famous ones in the Andes. If you climbed to the top of one of them, would you be closer to space than if you climbed to the top of Mount Everest?

Joseph Senne, an engineer/surveyor, did the calculations and had his numbers checked by the director of New York's Hayden Planetarium, Neil deGrasse Tyson, author of a new book on science and the cosmos, Death By Black Hole: And Other Cosmic Quandaries.

"When all the calculating is over," Senne says, "we think we have discovered the spot on Earth that is closet to the moon and outer space."

It is Mount Chimborazo in Ecuador. Yes, Ecuador.

Mount Chimborazo, in the Andes, is a 20,000-plus-foot peak sitting on top of a bulge on the Earth. Mount Everest is a 29,000-plus-foot peak sitting lower down on that same bulge. Because Chimborazo is a bump on a bigger part of the bulge, it is higher.

According to Senne, Chimborazo is 1.5 miles higher than Everest! Or, if you will, 1.5 miles closer to outer space.

If you define "highest" as highest from sea level, Mount Everest is still champion.

But if you want to stand on the place on Earth that is closest to the moon, that would be Mount Chimborazo!

Mount McKinley vs. Death Valley?

And as long as we're at it. using this same logic, which do you think is closer to the moon and stars, Death Valley in California or the top of Mount McKinley (also called Denali) in Alaska?

We asked David Metzler, a mountain-climbing mathematician who is also known as "Spireguy," one of Wikipedia's volunteer mountain statisticians, to do the calculations. Hear what he found.

And if you think that is wild, how about this: Which is higher, the Dead Sea (lowest point on the terrestrial Earth) or the top of Mount McKinley? Hear Spireguy's answer.


So what’s the most ‘super-habitable’ planet?

Here’s the researchers’ shopping list:

  • In orbit around a “K-type” dwarf star.
  • About 5-8 billion years old.
  • Up to 1.5 more massive than Earth and about 10% larger than Earth.
  • Mean surface temperature about 5°C higher than on Earth .
  • Moist atmosphere with 25–30% oxygen levels, the rest mostly inert gases (such as nitrogen).
  • Scattered land/water distributed with lots of shallow water areas and archipelagos (astronomers have no data on this for exoplanets).
  • Large moon (1–10% of the planetary mass) at moderate distance (10–100 planetary radii). (no data for this one)
  • Has plate tectonics or similar geological/geochemical recycling mechanism as well as a strong protective geomagnetic field. (also no data)

This is the position of KOI 5715—in the constellation of Cygnus, the Swan, and close to the famous . [+] "Summer Triangle" asterism.


Which Planet Is Closest To Earth?

We cannot answer this question with utmost surety because the distance of planets to earth keeps changing due to the range in the orbits of the planets. So it’s actually the position that indicates the planet closest to the earth. Besides, it also depends on the day, month and year.

But the planets closest to the Earth are Venus, Mars or Mercury. Mercury is never that close to Earth, and when it is, it happens once in tens of thousands of years. Venus, lying 162 million miles from our planet, seems to be the nearest planet to earth for the most time.


Can ET see us? Study finds many stars with prime Earth view

Outer Space Seeing Earth This illustration provided by the American Museum of Natural History depicts the planet Earth, center, with the Sun in the background. The line of spots across the center of the image indicates star systems which can see Earth as it goes in front of our Sun. (OpenSpace/American Museum of Natural History via AP) (Uncredited)

June 23, 2021 at 12:39 pm EDT By SETH BORENSTEIN

Feeling like you are being watched? It could be from a lot farther away than you think.

Astronomers took a technique used to look for life on other planets and flipped it around — so instead of looking to see what’s out there, they tried to see what places could see us.

Astronomers calculated that 1,715 stars in our galactic neighborhood — and hundreds of probable Earth-like planets circling those stars — have had an unobstructed view of Earth during human civilization, according to a study Wednesday in the journal Nature.

“When I look up at the sky, it looks a little bit friendlier because it’s like, maybe somebody is waving,” said study lead author Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University.

Even though some experts, including the late Stephen Hawking, warn against reaching out to aliens because they could harm us, Kaltenegger said it doesn't matter. If those planets have advanced life, someone out there could conclude that there is life back here based on oxygen in our atmosphere, or by the radio waves from human sources that have swept over 75 of the closest stars on her list.

“Hiding is not really an option,” she said.

One way humans look for potentially habitable planets is by watching them as they cross in front of the star they are orbiting, which dims the stars' light slightly. Kaltenegger and astrophysicist Jacqueline Faherty of the American Museum of Natural History used the European Space Agency's Gaia space telescope to turn that around, looking to see what star systems could watch Earth as it passes in front of the sun.

They looked at the 331,312 stars within 326 light-years of Earth. One light-year is 5.9 trillion miles. The angle to see Earth pass in front of the sun is so small that only the 1,715 could see Earth at some point in the last 5,000 years, including 313 that no longer can see us because we've moved out of view.

Another 319 stars will be able to see Earth in the next 5,000 years, including a few star systems where scientists have already spotted Earth-like planets, prime candidates for contact. That brings the total to more than 2,000 star systems with an Earth view.

The closest star on Kaltenegger’s list is the red dwarf star Wolf 359, which is 7.9 light-years away. It's been able to see us since the disco era of the mid 1970s.

Carnegie Institution for Science planetary scientist Alan Boss, who wasn’t part of the study, called it “provocative.” He said in addition to viewing Earth moving in front of the star, space telescopes nearby could spot us even if the cosmic geometry is wrong: “So intelligent civilizations who build space telescopes could be studying us right now.”

So why haven’t we heard from them?

It takes a long time for messages and life to travel between stars and civilizations might not last long. So between those two it’s enough to limit the chances for civilizations to exchange "emails and TikTok videos,” Boss said in his own email. “So we should not expect aliens to show up anytime soon.”

Or, Kaltenneger said, life in the cosmos, could just be rare.

What’s exciting about the study is that it tells scientists “where to point our instruments,” said outside astronomer Seth Shostak of the SETI Institute that searches for extraterrestrial intelligence. “You might know where to look for the aliens!”

Follow Seth Borenstein on Twitter at @borenbears.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

Copyright 2021 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.


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