Astronomy

ASTRONEWS

Rain

Standing

Light

from

stars

Earth at rest

Running

Earth moving

14 ASTRONOMY • DECEMBER 2018

When charged particles from the Sun slam into Earth’s

atmosphere, they impart energy that is subsequently

released as light, called an aurora. Although we know

much about how aurorae form, this process still holds

surprises — such as STEVE, a vibrant violet phenom-

enon that captured the attention of the professional

scientific community two years ago.

STEVE, which stands for Strong Thermal Emission

Velocity Enhancement, originally was dubbed a kind

of aurora. Now, a new study published August 20 in

Geophysical Research Letters concludes that STEVE is

not actually an aurora, after all.

“Right now, we know very little about it,” said Bea

Gallardo-Lacourt of the University of Calgary in

Canada, and lead author of the paper, in a press

release. “And that’s the cool thing, because this has

been known by photographers for decades. But for

the scientists, it’s completely unknown.”

Gallardo-Lacourt’s team made the discovery using

data from the National Oceanic and Atmospheric

Administration’s Polar Orbiting Environmental Satellite

17, which passed over an area in eastern Canada dur-

ing a STEVE event in 2008. That same event was also

captured by a ground-based camera project designed

to record auroral activity. By comparing the images

with the satellite data, the researchers confirmed that

STEVE was present. But the charged particles cascad-

ing through Earth’s ionosphere, previously believed to

cause STEVE and known to cause the aurora, weren’t.

This means STEVE and the aurora were not caused by

the same mechanism.

Gallardo-Lacourt’s team is now calling STEVE a kind

of “skyglow,” a new type of phenomenon not associ-

ated with aurorae. Skyglow is commonly associated

with light pollution, but in this case, STEVE’s skyglow is

structured and distinct. The team plans to look into

whether particle activity associated with STEVE is

causing the light directly, or whether the light is gen-

erated elsewhere in Earth’s atmosphere.

Whatever the cause, pinning down STEVE’s true

nature will ultimately improve our understanding of

Earth’s atmosphere and the processes that occur

within it. — A.K.

STEVE the aurora isn’t

an aurora, after all

Hubble highlights solar system gems

ELUSIVE NATURE. STEVE is a purple, ribbonlike

phenomenon that appears during an aurora. New research

has uncovered that STEVE is not caused by the same mechanism

that generates the northern lights. RYAN SAULT

WHAT IS STELLAR ABERRATION?

LEANING LIGHT. Anyone

who has attempted to run

through a wind-free rainstorm

has likely experienced a

strange phenomenon known

as aberration. This is where the

horizontal movement of a

running person causes

otherwise vertical rain to

appear to fall at an angle. The

faster a shelter-seeking person

is running, the more the rain

will appear to fall horizontally.

What you may not know is

that the movement of Earth

through space leads to a

similar effect called stellar

aberration. The vast majority

of telescopes used by

astronomers to investigate the

cosmos are either on Earth or

in orbit around it. Therefore,

the entire time these

telescopes collect light, they

are also moving with respect

to the distant stars. This

motion causes the starlight to

appear to come from a

position ahead of

the star’s true

position. — J.P.

FIRST OF MANY. The newly operational CHIME radio telescope detected its first fast radio burst (FRB) on August 1.

CHIME should spot more than a dozen FRBs per day once fully operational.

Generally, stellar

aberration causes

a star to appear up

to 20" ahead of its

true position.

FAST

FAC T

10

The number of times the crew of Apollo 8

circled the Moon, beginning December 24,

1968. In total, they spent about 20 hours
      in lunar orbit.

DOUBLE SHOT. NASA’s Hubble Space Telescope was ready for a great photo op — two planetary

oppositions — this summer. It snapped this photo of Saturn (left) a few weeks before its late June

opposition, and thanks to the planet’s significant tilt toward Earth, Hubble captured Saturn’s famous

features in incredible detail. The image shows the planet’s signature hexagon, caused by winds at

the north pole, and its prominent rings, which span eight times the radius of the planet. Hubble

also imaged Mars (right) just two weeks before opposition, but it was limited by the colossal dust

storm engulfing the planet. Despite those circumstances, the telescope still managed to capture

Mars’ white polar caps, its Sinus Meridiani feature, and dusty views of two massive impact craters:

Schiaparelli Crater along the equator and Hellas basin in the southern hemisphere. — A.J.

NASA, ESA, A. SIMON (GSFC AND THE OPAL TEAM, AND J. DEPASQUALE (STS

CI; NASA, ESA, AND STS

CI

ASTRONOMY

: ROEN KELLY