Astronomy - USA (2022-02)

Earth

INNER BELT

400-6,000 miles

(643-9,700 km)

OUTER BELT

8,400-36,000 miles

(13,400-58,000 km)

~250 miles (400 km)

INTERNATIONAL

SPACE STATION

GEOSTATIONARY

ORBIT

22,000 miles

(36,000 km)

Magnetic field lines

WWW.ASTRONOMY.COM 63

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AI

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.
The appearance and colors of the umbra, projected
onto the face of the Moon, provide a sort of mirror
showing what is happening in various layers of the
atmosphere here on Earth. Volcanoes send large
amounts of ash higher up into the stratosphere, along
with gases that chemically react to form additional
lingering aerosols. One of the ways scientists measure
the amount of volcanic aerosols in the atmosphere
(specifically the stratosphere) is through gauging any
possible increase in darkness during a lunar eclipse.
And of course, if the amount of ash is great enough,
the Moon may not be visible at all.
Steve Albers
Lead Scientist for Global Cloud Analysis, Spire Global,
Boulder, Colorado

QI

WHY DOES THE INTERNATIONAL
SPACE STATION ORBIT EARTH?
COULDN’T IT JUST REMAIN PARKED
OVER ONE SPOT?
Robert Chabak
Normandy Beach, New Jersey

AI

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.

Most of the ISS was assembled using NASA’s space

shuttle, which was designed to f ly in low Earth orbit. This

f leet of orbiting spacecraft was only able to achieve an

orbital altitude between 190 and 330 miles (304 to

528 km). Luckily, everything space agencies wanted to

study aboard the ISS, including microgravity and the

space environment, could be achieved in low Earth orbit.

There are a few other reasons to keep the ISS in a low

Earth orbit as well. Not only do launches and cargo ship-

ments get exponentially more expensive the higher the

station is, but they also get more dangerous.

There are two zones of radiation above the planet,

consisting of energetic charged particles trapped by

Earth’s magnetic field. These regions are called the Van

Allen belts. They wax and wane, but generally, the inner

belt sits at 400 to 6,000 miles (643 to 9,700 km) and the

outer belt stretches from 8,400 to 36,000 miles (13,400 to

58,000 km) above Earth. So, putting the ISS even a little

higher than its current orbit would expose the astronauts

living on the station to the hazards of the inner belt —

and reaching geostationary orbit would put them within

the outer radiation zone.

Caitlyn Buongiorno

Associate Editor

Two belts of

dangerous radiation

encircle Earth, as seen

in this illustration. The

International Space

Station’s current orbit

keeps it safe from the

inner belt. ASTRONOMY:

ROEN KELLY

THE VAN ALLEN BELTS