The Earth’s atmosphere is a total drag, especially if you’re trying to orbit our planet. So how low can you go?
The Earth’s atmosphere is a total drag, especially if you’re trying to orbit our planet. It’s a drag. Get it? Atmospheric drag. Drag. Drag.
Hi, my name is Fraser Cain. I’m the publisher of Universe Today, and sometimes my team lets me write my own jokes.
I could have started off this episode with a reference to the “Adama Drop” in-atmosphere viper deployment from BSG, but instead I went with a Dad joke. My punishment is drawing attention to it.
So how low can you go? And if you go low enough, will Ludacris appear in the mirror?
We all appreciate the Earth’s atmosphere and everything it does for you. With all the breathing, and the staying warm and the not having horrible bruises all over your body from teeny space rocks pummeling us.
I’ve got an alternative view. The Earth’s atmosphere is your gilded pressurized oxygenated cage, and it’s the one thing keeping you from flying in space.And as we all know, this is your destiny.
Without the atmosphere, you could easily orbit the Earth, a few kilometers over its surface. Traveling around and around the planet like a person sized Moon. Wouldn’t that be great?
Well, it’s not going to happen. As you walk through the atmosphere, you bonk into all the air molecules. You don’t feel it when you’re moving at walking speed, but go faster, like an airplane, and it’ll rock you like a hurricane.
Without constant thrust pushing against the atmosphere, you’ll keep slowing down, and when you’re trying to orbit the planet, it’s a killer. Our atmosphere is like someone is constantly pushing the brakes on the fly in space party.
If you’ve played Kerbal Space Program, you know the faster you’re traveling, the higher you orbit. Conversely, the slower you travel, the lower you orbit. Travel slow enough and you’ll eat it, and by it, I meant as much planet as you can co-exist with after a high speed impact.
Being more massive means more momentum to push against the atmospheric drag. But with a large surface area, it acts like a parachute, slowing you down.
Hey, I know something that’s super massive with a huge surface area. The International Space Station orbits the planet at an altitude between 330 km and 435 km.
Why such a big range? The atmosphere is constantly pushing against the ISS as it orbits the planet. This slows down the space station’s speed and lowers its orbit. It wouldn’t last more than a couple of years if it wasn’t able to counteract the atmospheric drag.
The International Space Station, photographed by the crew of STS-132 as they disembarked. Credit: NASA
Fortunately, the station has rockets to increase its speed, and a faster speed means a higher orbit. It can even get assistance from docked spacecraft. If the space station were to go any lower, it would require higher and higher amounts of thrust to prevent re-entry into the Earth’s atmosphere.
So what are the limits? Anything below 160 km altitude will essentially re-enter almost immediately, as it’s buffeted by the thicker atmosphere. You really wouldn’t last more than a few hours at that altitude, but above 800 km you could orbit for more than 100 years.
Geosynchronous satellites that orbit the Earth and transmit our television signals are at an altitude of about 42,000 km. Satellites that high are never coming back down. Well, maybe not never.
Want to enjoy your orbital experience? Make sure you get yourself to an altitude of at least 300 km, 400 km just to be safe. You should shoot for more like 800 km if you just don’t want to worry about things for a while.
Knowing these risks, would you be willing to travel to orbit with current technology? Tell us in the comments below.
Astronomers rely on the optics of their instruments, and there are some basic limits that you just can’t avoid. Whatever we look at is distorted by the optics, in fact, a basic property of light means that we’ll never get perfect optics. Here’s why we can’t “magnify and enhance” forever. Continue reading “Astronomy Cast Ep. 380: The Limits of Optics”
When massive objects crash into each other, there should be a release of gravitational waves. So what are these things and how can we detect them?
Who wants to bet against Einstein? You? You? What about you?
Sure, there were a few bumps, but the guy’s track record on relativity is spotless. He explained the strange way that Mercury orbits the Sun. He guessed astronomers would see stars deflected by the Sun’s gravity during a solar eclipse. He predicted that gravity would redshift light, and it took physicists 50 years to finally come up with an experiment to verify it.
Based on his predictions, scientists confirmed galaxies warp light with their gravity, photons get time dilated when they pass near the Sun, and clocks that travel at high speeds experience less time than clocks on Earth.
They’ve even tested gravitational redshift, frame-dragging and the equivalence principle. Which is a word salad we’ll cover in the future, or for those of you who can’t wait, google.
Every time Bertie made a prediction about Relativity, physicists have been able to verify via experimentation. And so, according to this fuzzy man with the giant brain, when massive objects crash into each other, or when black holes form, there should be a release of gravitational waves.
So what are these things and how can we detect them?
First, a quick review. Mass causes a warp in space and time. The Sun’s “gravity” isn’t a pulling force, it’s really an indentation that the Sun causes in the space around itself.
Planets think they’re moving in a straight line, but they’re actually pulled into a circle while traveling through this warped spacetime. Go home planets, you’re drunk.
The idea is when mass moves or changes, Einstein said that there should be gravitational ripples produced in spacetime.
Our problem is that the size and effect of gravitational waves is incredibly small. We need to find the most catastrophic events in the Universe if we hope even detect them.
A supernova detonating asymmetrically, or two supermassive black holes orbiting each other, or a Galactus family reunion; are the magnitude of events we’re looking for.
The most serious attempt to detect gravitational waves is the Laser Interferometer Gravitational-Wave Observatory, or LIGO detector, in the United States. It has two facilities separated by 3000 km. Each detector carefully watches for any gravitational waves passing through by the length of time it takes for laser pulses to bounce within a 4km long sealed vacuum.
Laser Interferometer Gravitational-Wave Observatory Hanford installation – each arm extends for four kilometres. Credit: Caltech.
If a gravitational wave is detected, the two observatories use triangulation to determine its magnitude and direction. At least, that was the plan from 2002 to 2010. The problem was, it didn’t detect any gravitational waves for its entire run.
But hey, this is a job for science. Unbowed, the steely-eyed researchers rebuilt the equipment, improving its sensitivity by a factor of 10. This next round starts in 2015.
Scientists have proposed space-based instruments that could provide more sensitivity and increase the chances of detecting a gravitational wave.
Physicists assume this is a question of “when”, not “if” that gravitational waves will be detected, as only a fool bets against Einstein. Well, that and gravitational waves have already been detected… indirectly.
By watching the extremely regular energy blasts coming from pulsars, astronomers track exactly how quickly they’re radiating their energy away due to gravitational waves. So far, all the observations perfectly match the predictions of relativity. We just haven’t detected those gravitational waves directly… yet.
So, good news! Assuming the physicists and Einstein are right, we should see the detection of a gravitational wave in the next few decades, wrapping up a series of predictions about how insanely strange our Universe behaves.
Should we dig deeper into relativity, Einstein and his predictions? Tell us in the comments below.
Host: Fraser Cain (@fcain) Special Guest: This week we welcome Stephen Fowler, who is the Creative Director at InfoAge, the organization behind refurbishing the TIROS 1 dish and the Science History Learning Center and Museum at Camp Evans, Wall, NJ.
Everything eventually dies, even galaxies. So how does that happen? Time to come to grips with our galactic mortality. Not as puny flesh beings, or as a speck of rock, or even the relatively unassuming ball of plasma we orbit.
Today we’re going to ponder the lifespan of the galaxy we inhabit, the Milky Way. If we look at a galaxy as a collection of stars, some are like our Sun, and others aren’t.
The Sun consumes fuel, converting hydrogen into helium through fusion. It’s been around for 5 billion years, and will probably last for another 5 before it bloats up as a red giant, sheds its outer layers and compresses down into a white dwarf, cooling down until it’s the background temperature of the Universe.
So if a galaxy like the Milky Way is just a collection of stars, isn’t that it? Doesn’t a galaxy die when its last star dies?
But you already know a galaxy is more than just stars. There’s also vast clouds of gas and dust. Some of it is primordial hydrogen left from the formation of the Universe 13.8 billion years ago.
All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing baby stars every year. Sadly, ours has used up 90% of its hydrogen, and star formation will slow down until it both figuratively, and literally, runs out of gas.
The Milky Way will die after it’s used all its star-forming gas, when all of the stars we have, and all those stars yet to be born have died. Stars like our Sun can only last for 10 billion years or so, but the smallest, coolest red dwarfs can last for a few trillion years.
The Andromeda Galaxy. Credit: Adam Evans
That should be the end, all the gas burned up and every star burned out. And that’s how it would be if our Milky Way existed all alone in the cosmos.
Fortunately, we’re surrounded by dozens of dwarf galaxies, which get merged into our Milky Way. Each merger brings in a fresh crop of stars and more hydrogen to stoke the furnaces of star formation.
There are bigger galaxies out there too. Andromeda is bearing down on the Milky Way right now, and will collide with us in the next few billion years.
When that happens, the two will merge. Then there’ll be a whole new era of star formation as the unspent gas in both galaxies mix together and are used up.
Eventually, all galaxies gravitationally bound to each other in this vicinity will merge together into a giant elliptical galaxy.
We see examples of these fossil galaxies when we look out into the Universe. Here’s M49, a supermassive elliptical galaxy. Who knows how many grand spiral galaxies stoked the fires of that gigantic cosmic engine?
Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.
Elliptical galaxies are dead galaxies walking. They’ve used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.
As long as galaxies have gas for star formation, they’ll keep thriving. Once it’s gonzo, or a dramatic merger uses all the gas in one big party, they’re on their way out.
What could we do to prolong the life of our galaxy? Let’s hear some wild speculation in the comments below.
When he wasn’t puzzling the mystery of alien civilizations, Enrico Fermi was splitting atoms. He realized that when atoms were split, the neutrons released could go on and split other atoms, creating a chain reaction – and the most powerful weapons ever devised. Continue reading “Astronomy Cast Ep. 379: Fermi’s Atom Splitting”
If aliens were heading towards the Earth, would we see them coming?
Classic sci fi trope time. The air force detects a fleet of alien spacecraft out past Jupiter, leaving enough time to panic and demonstrate what awful monsters we truly are before they come ring our bell.
Is that how this would work?
Imagine a pivotal scene in your favorite alien mega disaster movie. Like the one where the gigantic alien ships appear over London, Washington, Tokyo, and Paris and shoots its light-explody ray, obliterating a montage of iconic buildings. Demonstrating how our landmark construction technology is nothing against their superior firepower.
What could we do? We’re merely meat muppets with pitiful silicon based technology. How could we ever hope to detect these aliens with their stealth spacecraft and 3rd stage guild navigators? If we’re going to do this, I’m going to make up some rules. If you don’t like my rules, go get your own show and then you can have your own rules.
Alternately, as some of you are clearly aware, you can rail against the Guide To Space in the comments below. Dune reference notwithstanding, I’m going to assume that aliens live in our Universe and obey the laws of physics as we understand them. And I know you’re going to say, what if they use physics we haven’t discovered yet?
Then just pause this video and get that out of your system. You can make that your first decree against the state right in the comments below. As I was saying, physical aliens, physical universe. We’ll discuss the metaphysical aliens in a magic universe in a future video. The ones that have crystals and can heal your liver through the power of song.
A basic rule of the Universe is that you can’t go faster than the speed of light. So I’m going to have any aliens trying to attack us traveling at sublight speeds.
So, we’ll say they’ve got access to a giant mountain of power. They can afford to travel at 10% the speed of light, which means before they get to us, they have to slow down. At this speed, deceleration is expensive. We’d see the energy signature from their brakes long before they even reached Earth.
Let’s say they’re passing the orbit of the dwarf planet Pluto, which is 4 light-hours away. Since they’re travelling at 10% the speed of light, we’d have about 40 hours to scramble jet fighters, get those tanks out onto the streets and round up Will Smith, Jeff Goldblum and Bruce Willis to hide behind.
A composite image with Chandra data (purple) showing a “point-like source” beside the remains of a supernova, suggesting a companion star may have survived the explosion. Credit: X-ray: NASA/CXC/SAO/F.Seward et al; Optical: NOAO/CTIO/MCELS, DSS
Would we even notice? Maybe, or maybe not. A growing trend in astronomy is scanning the sky on a regular basis, looking for changes. Changes like supernova explosions, asteroids and comets zipping past, and pulsating variable stars.
One of the most exciting new observatories under construction is the Large Synoptic Survey Telescope in Chile. Once it begins regular operations in 2022, this array of telescopes will photograph the entire sky in fairly high resolution every few nights.
Computers will process the torrent of data coming from the observatory and search for anything that changes. What if they engage their cloak?
Actually (push glasses up your nose) the laws of physics say that the aliens can’t hide the waste heat from whatever space drive they’re using. We’re actually pretty good at detecting heat with our infrared telescopes.
A space drive decelerating a city-sized alien spacecraft from a significant portion of the speed of light would shed a mountain of heat, and that’s all heat we might detect.
Astronomers have been searching for alien civilizations by looking for waste heat generated by Dyson spheres encapsulating entire stars or even all the stars in a galaxy. Nothing’s turned up yet. Which I for one, find a little suspicious.
Freemon Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
If you’re from an alien race who’s planning to invade. Cover your ears. If aliens wanted to catch us off guard, they can use one of the oldest tricks in the aerial combat book, known as the Dicta Boelcke. They can fly at us using the Sun as camouflage. A rather large portion of the sky is completely obscured by that glowing ball of fiery plasma. It worked in WW1, and it’ll still work now.
Okay, aliens you can listen in again. Everyone else might want to mute the next part, as it’s not terribly reassuring. Astronomers often discover asteroids skimming by the Earth just after they’ve just gone past. That’s because they hurl at us from the Sun, just like clever aliens.
To spot those asteroids, we’ll need to deploy a space-based sky survey that can watch the heavens from a different perspective than Earth. Plans for this kind of mission are actually in the works.
Even with our rudimentary technology, we’d actually stand a pretty good chance of noticing the alien attack vessels before they actually arrived at centre of Sector 001. It’ll get better with automated observatories and space-based sky surveys.
Of course, there’s little we can do if we did know the aliens were coming. We’d be best to start with some kind of deterrent, contaminate all our fresh water, load our livestock up on antibiotics and cover our cities in toxic smog to deter the harvesting of our citizens.
Do you think we’d stand a chance against an alien invasion? Tell us how we’d do in the comments below.
The Solar System is 4.5 billion years old, but the Universe is much older. What was here before our Solar System formed?
The Solar System is old. Like, dial-up-fax-machine-old. 4.6 billion years to be specific. The Solar System has nothing on the Universe. It’s been around for 13.8 billion years, give or take a few hundred million. That means the Universe is three times older than the Solar System.
Astronomers think the Milky Way, is about 13.2 billion years old; almost as old as the Universe itself. It formed when smaller dwarf galaxies merged together to create the grand spiral we know today. It turns out the Milky Way has about 8.6 billion years of unaccounted time. Billions and billions of years to get up to all kinds of mischief before the Solar System showed up to keep an eye on things.
Our Galaxy takes 220 million years to rotate, so it’s done this about 60 times in total. As it turns, it swirls and mixes material together like a giant space blender. Clouds of gas and dust come together into vast star forming regions, massive stars have gone supernova, and then the clusters themselves have been torn up again, churning the stars into the Milky Way. This happens in the galaxy’s spiral arms, where the areas of higher density lead to regions of star formation.
So let’s go back, more than 4.6 billion years, before there was an Earth, a Sun, or even a Solar System. Our entire region was gas and dust, probably within one of the spiral arms. Want to know what it looked like? Some of your favorite pictures from the Hubble Space Telescope should help.
Here’s the Orion, Eagle, and the Tarantula Nebulae. These are star forming regions. They’re clouds of hydrogen left over from Big Bang, with dust expended by aging stars, and seeded with heavier elements formed by supernovae.
The Orion Nebula. Image Credit: Vasco Soeiro
After a few million years, regions of higher density began forming into stars, both large and small. Let’s take a look at a star-forming nebula again. See the dark knots? Those are newly forming stars surrounded by gas and dust in the stellar nursery.
You’re seeing many many stars, some are enormous monsters, others are more like our Sun, and some smaller red dwarfs. Most will eventually have planets surrounding them – and maybe, eventually life? If this was the environment, where are all those other stars?
Why do I feel so alone? Where are all our brothers and sisters? Where’s all the other stuff that’s in that picture? Where’s all my stuff?
TRAPPIST First Light Image of the Tarantula Nebula. Credit: ESO
Apparently nature hates a messy room and a cozy stellar nest. The nebula that made the Sun was either absorbed into the stars, or blown away by the powerful stellar winds from the largest stars. Eventually they cleared out the nebula, like a fans blowing out a smoky room.
At the earliest point, our solar nebula looked like the Eagle Nebula, after millions of years, it was more like the Pleiades Star Cluster, with bright stars surrounded by hazy nebulosity. It was the gravitational forces of the Milky Way which tore the members of our solar nursery into a structure like the Hyades Cluster. Finally, gravitational interactions tore our cluster apart, so our sibling stars were lost forever in the churning arms of the Milky Way.
We’ll never know exactly what was here before the Solar System; that evidence has long been blown away into space. But we can see other places in the Milky Way that give us a rough idea of what it might have looked like at various stages in its evolution.
What should we call our original star forming nebula? Give our own nebula a name in the comments below.
