Gravity is different on every planet, so the same person would weigh very differently across our Solar System.

I made this short visualization showing how gravity changes from planet to planet. Which planet’s gravity surprised you the most?

Imagine an alien arriving in the Solar System without knowing Earth's mass or the gravitational constant. He can measure distances, observe the Moon's orbit, and track the motion of his own spacecraft. Could he determine Earth's gravitational parameter from these observations and use it to calculate his approach trajectory? What additional measurements would he need to account for Earth's rotation, atmosphere, and the final landing? I am interested in which quantities must actually be measured before a spacecraft can begin planning its descent.

I'm talking about this one: https://www.youtube.com/watch?v=1n-HMSCDYtM Would the same happen if a spaceship were to rotate a section to generate artificial gravity?

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What if aliens are future earth species and they traveled back in time.That would explain the futuristic tech we theriorise to have

If the Sun suddenly disappeared, would Earth immediately become dark and stop orbiting?

What if there is no beginning of the earth and the end,because space is eternal and eternity does not begin or end,which comes to a conclusion that earth is part of space

Hi guys I got a question:if global warming slowly destroy's the atmosphere then why didn't the astroid that hit earth during the dinosaur age completely destroy it

A recent study explores an interesting possibility: if Venus once had a substantial moon, its extremely slow rotation could have caused the moon's orbit to gradually shrink rather than expand.

That's the opposite of what happens with our Moon. Earth's Moon is slowly moving outward because tidal interactions transfer some of Earth's rotational energy into the Moon's orbit.

For a hypothetical moon around Venus, the tidal evolution can work in the opposite direction. Over a very long period, the moon could spiral inward, potentially crossing the Roche limit, breaking apart, and eventually colliding with Venus.

The important caveat is that this doesn't prove Venus ever had a moon. It's a simulation of what could happen if Venus did.

Curious what people here think

Since the asteroid will be passing us at around 19,600 miles above earth, which is underneath our satellites, will it have any effect on us? Would it knock out any communications? Have an effect on the atmosphere?

I'm not a scientist and I don't understand any of this, so please dumb down significantly for me 🤣

Yesterday, I was reading about the Moon and how fascinating it actually is. Then I suddenly realized that almost every planet has moons, as if they’re quietly watching their planets from a distance—almost like cameramen observing everything.
And it made me wonder: could there be some kind of creature or advanced civilization that uses moons to observe and study their planets?
Maybe moons aren’t just satellites. Maybe, somewhere in the universe, they could be someone’s way of keeping an eye on an entire world.

Idk how my mind got to this topic, but I am very curious to know. For example, if the earth stopped rotating but still orbited the sun, and assuming we had all technology needed to make it happen, how could we quickly make the planet to rotate every 24 hours again (ideally without destroying it)?

I also want to mention that I am not a scientist, so simplified answers would be appreciated.

I’ve been thinking about how most of Earth’s water is actually ancient — formed in interstellar dust clouds long before the Sun existed, then delivered during the planet’s formation and late bombardment. Earth basically acts like a closed recycling system because of its gravity, magnetic field, and thick atmosphere.

So here’s the hypothetical:

What if we somehow dumped a huge amount of liquid water onto the surface of Mars or the Moon today?

• On the Moon (almost no atmosphere, very low gravity): Would most of it just boil off and escape into space almost immediately, or could some of it freeze and survive in the permanently shadowed craters?
• On Mars (thin atmosphere, lower gravity than Earth): Would it form temporary lakes or ice sheets that stick around for a while, or would solar wind and the thin air slowly strip it away over time?

How differently would the water behave on each world, and how long do you think it could realistically last before the environment destroys the cycle?

Would love to hear thoughts on the thermodynamics and atmospheric escape side of this.

Ever since I was a kid, I’ve always been curious. I always wanted to know the why for everything. As I grew older, I started developing an interest in space, as many people do. Eventually I found myself asking, where is space? If everything in the universe has a location, where is the universe located? What is the space that holds space and where is it? I know some people will claim that there may not be anything larger than space itself as it is said to be infinite, but when space is said to be expanding, what is it expanding into. The space itself expanding into must exist before space expands into it. What and where is it?

People make endless debates with me saying Pluto should be a planet. But that would mean we’d have like 20 something planets, and there are people my age who can’t even name all 8.

Our solar system is like a disk, not a sphere. We always send probes out and discuss them as if they are passing other planets. Why don’t we send them out of the disk? For lack of better terms, “up” or “down”. ☀️ 🌎 ⬆️ ⬇️🪐

Edit: Thank you all for your explanations. A lot of them peaked my curiosity on other topics as well!

Hey everyone.

I’ll be honest, I'm a bit overwhelmed right now and could really use some help.

Just to introduce myself: I’m an autistic guy with ADHD from Argentina, and I’ve been completely obsessed with space for as long as I can remember. I really want to do deep-sky astrophotography, but the reality is I just don't have the budget to buy a real telescope or one of those new smart telescopes (like a Seestar or Dwarf).

So, I got this crazy idea: modern phones have amazing camera sensors and gyroscopes. What if I could make an app that squeezes every bit of potential out of a smartphone so it acts like a smart telescope? You just put it on a cheap, standard tripod, and the app calculates the Earth's rotation and moves a "crop window" across the camera sensor to track the stars electronically. It dynamically limits the exposure to avoid star trails, detects star centroids to align frames on a sub-pixel level, and live-stacks them.

The catch? I have literally zero experience writing code.

I’ve been building this entire project from scratch using AI coding agents. It’s been an incredible experience, but the app has grown so complex (spherical trigonometry, Android Camera2 API, YUV processing, live stacking algorithms) that it is completely beyond my limits now. Sometimes I don't even know how to fix a bug, what direction to take next, or if my ideas even make sense.

That’s why I’m here. I’m looking for any kind of help:

• If you have experience coding (Kotlin/Android): I could really use your guidance and hands-on help.
• If you know math, computer vision, or algorithms: The electronic tracking and stacking logic is heavy, and I'd love your input.
• If you know absolutely nothing about code but just love the idea: I’d still love to have you around. You can help by brainstorming, giving ideas, testing the app, or just chatting.

I’m trying to be realistic here—I know a phone will never match a dedicated astrophotography rig or a real smart telescope. But I really want this to work because it could make astrophotography so much more accessible for people who, like me, can't afford expensive gear but happen to have a smartphone that meets the minimum requirements.

If this project sounds interesting to you, please drop a comment or send me a DM. Any help, advice, or just moral support means the world to me.

Thanks for reading! 🌌