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Ask Astro: How can a photon be massless?

How can a photon of light carry energy but also be considered massless? Doesn’t Einstein’s E = mc2 make that impossible?. Einstein’s famous mass-energy equivalence equation, or E = mc2, is actually a special case of a slightly longer formula known as the energy-momentum relation, which is written out as E2 = p2c2 + m2c4.
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Ask Astro: How far away is the cosmic microwave background?

The cosmic microwave background (CMB) is the radiation allowed to freely propagate after the universe cooled enough for electrons to combine with atomic nuclei to form neutral atoms some 300,000 years after the Big Bang, or roughly 14 billion years ago. This CMB radiation was mostly in the form of near-infrared light, but the wavelength of the CMB light has been stretched by the expansion of space so much it now falls in the microwave range we see today. This expansion of the universe describes the phenomenon whereby the distance between any two points in space gradually increases over cosmic time. So, the CMB source is 40 billion light-years away and not 14 billion light-years away, as one might expect.
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Ask Astro: Does our Oort Cloud overlap with Alpha Centauri’s?

Does our Oort Cloud overlap with Alpha Centauri’s?. About 2,000 to 5,000 astronomical units (AU; where 1 AU is the average distance between Earth and the Sun) from the Sun lies the beginning of the Oort Cloud. For context, the Voyager spacecrafts — the human-made objects that have traveled farthest from our Sun — will cross this inner edge of our solar system in about 300 years. From there, the Oort Cloud stretches to about 10,000 to 100,000 AU (0.16 to 1.6 light-years), according to NASA. But keep in mind this outer boundary is pretty nebulous, so there is no hard line where the Oort Cloud ends.
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Ask Astro: How is Earth the only known planet with active plate tectonics?

How is it that Earth is the only known planet with active plate tectonics?. Earth is special in that it has two things that other terrestrial planets don’t: an abundance of internal heat, from when our planet was molten rock, and liquid water. To understand why our planet is unique in this regard, let’s first look at Earth versus Mars.
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Ask Astro: How far could a pro golfer hit a ball on the Moon?

Some 50 years ago, Alan Shepard hit some golf balls on the Moon. Just how far could a tour pro hit a golf ball on the Moon if they weren’t encumbered by a spacesuit?. Alan Shepard shanked his first shot into a crater, but estimated that his second reached a distance of about 600 feet (183 meters). Recent evidence from remastered photos taken during the mission, however, suggests that Shepard managed to only hit his second golf ball some 120 feet (36.5 m).
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Ask Astro: Why will Europa Clipper orbit Jupiter instead of Europa?

Why will Europa Clipper orbit Jupiter instead of Europa?. NASA’s Europa Clipper spacecraft is scheduled for launch in 2024, carrying 10 instruments that will assess the habitability of Jupiter’s moon Europa. The craft will follow up on discoveries by the Galileo mission of the 1990s, which orbited Jupiter and made multiple flybys of both the planet and its major satellites. As you point out, Europa Clipper will orbit Jupiter. However, it will solely focus on Europa, performing some 50 close passes of the ocean-sporting moon during its primary mission.
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Ask Astro: Could the International Space Station park in one spot over Earth?

Why does the International Space Station orbit Earth? Couldn’t it just remain parked over one spot?. The International Space Station (ISS) orbits Earth at an average altitude of 200 to 250 miles (322 to 402 km). A geostationary orbit, or one where the ISS would stay parked above the same spot on Earth, would require the station to have an altitude around 22,000 miles (36,000 km) above the equator. In theory, that would work, but the ISS had one major obstacle holding it back from reaching those heights: the space shuttle.
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Ask Astro: What are the largest Near-Earth Objects?

What is the largest asteroid and comet considered to be a near-Earth object? How large are they?. Doomsday impactors are a staple of modern science fiction. The most famous real-world example of an impact wiping out much of the life on Earth is, of course, the object that took out the dinosaurs some 66 million years ago.
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Ask Astro: How would a volcanic eruption affect a lunar eclipse?

The Moon can appear red during a total lunar eclipse. What does the eclipsed Moon look like after a recent eruption leaves a large amount of volcanic ash in the atmosphere?. During a total lunar eclipse, the Moon passes through Earth’s shadow, called the umbra. Our natural satellite isn’t completely dark during the event, however. Earth’s atmosphere bends, or refracts, sunlight that passes within a few miles of the ground (in the lower troposphere) enough to reach near the umbra’s center. Not all the light reaches that point, however. Air molecules tend to scatter blue light more than red, which is why the Moon often appears reddish during these events.
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Ask Astro: Is Sirius part of the Milky Way? Does it have any planets?

Is Sirius part of the Milky Way? Does it have any known planets?. Sirius is the brightest star in the Northern Hemisphere. In order to see a pointlike star with your naked eye, it must be relatively close to us; this means that all the stars you can see in the night sky are within the Milky Way Galaxy. Resolving individual stars in other nearby galaxies, such as Andromeda in the Northern Hemisphere or the Large and Small Magellanic Clouds in the Southern Hemisphere, requires professional equipment like the Hubble Space Telescope.
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Ask Astro: What is the Caloris Basin on Mercury — and how did it form?

What happened to the debris from the collision that formed the Caloris Basin on Mercury? Why didn’t it form a moon?. Mercury’s Caloris Basin is about 950 miles (1,525 kilometers) across. For comparison, the state of Texas is 773 miles (1,244 km) wide. The Moon has a similarly sized impact crater, Mare Orientale.
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Ask Astro: What fuel do spacecraft use to explore the distant solar system?

What kind of fuel do spacecraft use to explore the outer solar system and beyond?. Sir Isaac Newton’s first law of motion states that an object at rest stays at rest and an object in motion stays in motion with the same speed unless acted upon by an outside force. And in space, the only thing to slow down a spacecraft is gravity.
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Ask Astro: The universe is full of dust — what’s it made of?

The word dust comes up often in descriptions of galaxies and elsewhere. What is the nature of dust?. To most people, dust can be any combination of small particles of soil, rock, human skin, human or animal dander, pollen, and tiny bits of fiber. But space dust is different from the dust we’re familiar with here on Earth.
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Ask Astro: Are meteorites radioactive?

Do meteorites emit a high degree of radiation when they fall to Earth? Should precautions be taken when handling them?. On average, around 500 meteorites fall to Earth each year. Any radioactive elements contained in a meteorite are no more significant than in ordinary terrestrial rock. Although meteorites aren’t harmful to humans, we can actually be pretty harmful to them. Our hands are covered in oils and microbes, both of which can contaminate the meteorite and degrade its surface.
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Tribute to 'striking, joking' ex-UB40 member Astro

Ex-UB40 member Terence Wilson, better known as Astro, had a "very striking presence", a music expert said. Astro, 64. who performed in the Birmingham reggae pop band for more than 30 years, died after a short illness, his current band confirmed. He was "such a lovely person", said Jez Collins,...
MUSIC

UB40 founding member Astro dies following short illness

London (CNN) — British vocalist and founding member of UB40 Terence Wilson, better known by his stage name Astro, has died after a short illness, his current band confirmed. "We are absolutely devastated and completely heartbroken to have to tell you that our beloved Astro has today passed away after a very short illness," a statement on Ali Campbell and Astro's Twitter account said on Saturday. "The world will never be the same without him."
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