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EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH...

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How large is

the universe?

We really don’t know the answer,

but we know that it’s at least as

large as the Big Bang and cosmic

expansion tell us.

The concept of the size of the universe

has taken huge strides forward in just

the last few years. There was a time

not long ago when astrophysicists

didn’t know how big the cosmos is.

The Big Bang theory reminds us that

once the universe was small. We know

the fastest any radiation can travel is

the speed of light. We also know the

universe is 13.8 billion years old.

At first blush, you might expect

radiation across the universe to

expand by something like 30 billion

light-years after that time. But that’s

too simplistic. The Big Bang wasn’t

like a bomb going off; space itself

expands over time so that 1 centimeter

in the early cosmos becomes 2 centi-

meters and so on. Because of space-

time’s expansion, we know the

universe is at least 93 billion light-

years across.

But there’s a major proviso to that

number, which refers to the visible

universe. Our visible universe may not

be the entire universe, and on top of

that, some cosmologists even believe

the cosmos could be infinite.

So at best, we can say the universe

is at least 93 billion light-years across,

which is a pretty good hike.

— David J. Eicher

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COMET WATCH

Rosetta passed within 4

miles (6 kilometers) of

Comet 67P/Churyumov-

Gerasimenko, giving

scientists their best

view yet.

#YEAROFPLUTO

NASA released New

Horizon’s latest long-

distance look at Pluto to

celebrate the birthday

of the world’s finder,

Clyde Tombaugh.

THE PERFECT RING

Hubble shots of Beta

Pictoris, the only stel-

lar debris disk with an

imaged giant planet, saw

little change in 15 years,

implying near uniformity.

The universe holds at least 125 billion galaxies, and may contain far more than that, a number that seems staggering compared

with a single galaxy like NGC 6946.

TONY HALLAS (NGC 6946); ESA/ROSETTA/NAVCAM – CC BY-SA IGO

3.0 (COMET WATCH);

NASA/APL/S

WRI (#YEAROFPLUTO); NASA/ ESA/D. APAI AND G. SCHNEIDER (UNIV. OF ARIZONA) (THE PERFECT RING)