PHOENIX — Without fail, when a SpaceX rocket launches around sunset from Vandenberg Space Force Base in California, the 12News phones will start ringing.
"We just saw a spaceship in the sky!" one caller told us a few years ago.
"There was something that looked like a comet or an asteroid," said another voicemail.
And it's easy to see why people would think it's something out of this world. When they're visible from Arizona, SpaceX rocket launches look like giant white (or sometimes rainbow-colored) comets or streaks in the sky.
Luckily, Arizona has a lot of rocket scientists to choose from to explain why they look like this.
The Twilight Phenomenon
Dr. Vishnu Reddy is a scientist at the University of Arizona in Tucson. He's worked for the Jet Propulsion Laboratory, studies space situational awareness and basically ... knows a lot about space.
He told 12News the reason those rockets light up the sky is not because the engines burn brightly (although they do), it's because of something called the Twilight Phenomenon.
"The sun might have set for us here in Arizona, but it hasn't set in California," Reddy said. "So it's catching that sunlight and reflecting off."
Basically, the rocket launches far away, in California. but it goes so high that we can see it in Arizona. And when we see it, it's not in the shadow of nightfall, even though Arizona is. The "glow" is sunlight hitting the exhaust trail, even while we perceive the sky to be black.
"If you are at the top of a mountain, you can see the sunset much longer than people at the base of the mountain," Reddy said. So, think of the rocket as the top of the mountain while you're at the bottom.
We're not Florida
So why don't all rocket launches look like that?
Reddy said it's a combination of the time of day, the direction of the rocket's travel, and the launch point.
SpaceX typically launches to the southwest of Los Angeles at an angle to take it away from populated areas. The rockets tip at a certain point and fly more horizontally to the ground than vertically, almost in a dogleg path.
But rockets in Florida, like those that launched the Space Shuttle, or even SpaceX's rockets in Florida, don't do that.
"If you're in Florida," Reddy said, "the rockets are launching right on top of you. You do get the plume, you do get the contrails and other things, but you're not going to be seeing what we're seeing."
Starlink
And once the rocket gets into orbit, the 12News phone starts ringing again. Because this next mission is to release a series of Starlink satellites.
Starlink is a satellite Internet provider with thousands of tiny satellites circling the Earth.
But when they're released, they initially form a tight line that's visible from the ground. It looks like a string of bright lights moving all together.
They eventually spread out more to cover more area.
This next SpaceX mission is now set to launch no earlier than Saturday, March 30.
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