(JTA) — Overnight between Thursday and Friday, an arresting image appeared on social media: On the right, streaks of fire shot out into the night sky — rockets heading for a group of buildings illuminated in the darkness.

But on the other side of the photo, another cluster of lights, spread out like the tentacles of a jellyfish, was there to meet each of the rockets and knock it down before it could cause any damage.

The photo captured the Iron Dome, a missile defense system introduced in Israel a decade ago that has fundamentally changed how its wars are fought. The Iron Dome is a radar-guided tool that allows Israel to pinpoint and intercept missiles headed for its civilian areas, which enables ordinary Israelis to survive, and even live their lives, in the midst of an unending barrage of rocket fire from militant groups in Gaza.

As of Friday, eight Israeli civilians have died in this week’s fighting, and Israelis still need to run to bomb shelters when under fire. But the Iron Dome has intercepted 90% of Gaza rockets that were headed toward populated areas, rendering the vast majority of the more than 2,000 rockets fired by militant groups ineffective.

Here’s what the Iron Dome is, how it works — and why its success has sparked criticism of Israel.

Iron Dome uses radars to stop incoming missiles. 

On the ground, the Iron Dome looks like a set of beige columns arranged in a box, tilted onto their side and placed on wheels.

But the technology that makes it so valuable is a radar that is able to pick bombs out of the sky. The Iron Dome’s radar  technology, manufactured in the United States, works in four steps:

First, it identifies projectiles in the sky. Then, it determines whether the projectile is a bird, an airplane or a bomb. Then comes the most crucial part: It determines the arc of the missile, which allows it to find both the target and the missile launcher. Then, if the missile is headed toward a populated area, the system directs its own bomb to intercept the missile and explode it before it lands.

The entire process is automatic and takes a couple minutes, an Israeli weapons manufacturer told the Jewish Telegraphic Agency in 2013. The batteries can be moved around or stationed permanently in one location.

It isn’t foolproof. Hamas has sent barrages of more than 100 rockets in a short span of time at individual cities, which means that, even if Iron Dome is 90% effective, some bombs get through. And even when the system catches the rockets, shrapnel still falls to the ground.

That’s why Israelis still run to shelters every time sirens go off, warning of incoming missiles.

It was built and maintained with U.S. funding. 

The Iron Dome was built and has been maintained with billions of dollars in funding from the United States. It was first approved in 2007, and shot down its first missiles in 2011. Each Iron Dome interceptor costs an estimated $40,000, and in prolonged conflicts with Hamas, Israel uses it hundreds of times.

As of 2018, the U.S. spent more than $6 billion on missile defense aid to Israel, which covers Iron Dome and other, similar systems. In the middle of the Gaza War in 2014, the Obama administration provided $225 million in aid to fund the system’s continued operation. In 2018, the Trump administration provided another $705 million.

It means Israelis can (kind of) continue to live their lives during a war. 

Before the Iron Dome, Israelis had to rely on warning sirens and bomb shelters to protect them, which gave them, in some cases, a matter of seconds to find shelter.

As Palestinian militants’ missiles became more precise and traveled farther distances, targeting not just Gaza border cities but Tel Aviv and Jerusalem, the Iron Dome played an increasingly essential role for a growing number of Israelis.

It was first deployed in 2011, and was used constantly in Israel’s conflicts with Gaza in 2012, 2014 and since.

While Israelis still run for cover every time a siren wails, and while civilians are still killed, the Iron Dome has allowed society to continue functioning at a lower risk. But as Hamas’ missile technology improves, it’s possible that the Iron Dome could become less effective.

As of now, though, Israelis are grateful. During the 2014 war, Israelis could buy a t-shirt in the “I love NY” style that replaced “NY” with a picture of an Iron Dome battery.

Gaza does not have an equivalent system for its population. 

While Israelis love the Iron Dome for protecting them from bombs, Palestinians and their advocates have said that the system creates a disparity in the fighting: Gaza residents have no such protection from Israeli airstrikes, such that Palestinian death tolls are consistently far higher in Gaza during conflicts.

During this conflict, more than 100 Palestinians and nine Israelis have died. In the 2014 conflict, more than 2,100 Palestinians and more than 70 Israelis died.

But in the previous war in Gaza, fought in 2008-09, before the Iron Dome was developed, the death toll was similarly lopsided: nearly 1,400 Palestinians and 13 Israelis.

Still, along with accusing Israel of targeting civilians in its strikes, critics of Israeli actions say that the lack of protections in Gaza leads to an unjust divide. Rep. Ilhan Omar called Israeli airstrikes “terrorism” and lamented on Twitter this week that Palestinians did not have Iron Dome.

“Israeli air strikes killing civilians in Gaza is an act of terrorism,” she tweeted on Monday. “Palestinians deserve protection. Unlike Israel, missile defense programs, such as Iron Dome, don’t exist to protect Palestinian civilians.”

Israeli officials say the fact that Israel has invested in alliances and technology that protect their citizenry should not be cause for blame.

“The fact that there aren’t more casualties in Israel does not mean that Hamas isn’t trying to kill Israeli civilians,” the Israel Defense Forces tweeted Friday morning. “It simply means that the IDF is preventing them from doing so at an incredible level.”