Astronomy - 06.2019

ASTRONEWS

• 400° –300° –200° –100°

–200° –100° 0° 100° 200°

0° 100° 200° 300° 400°

400°

800° 900°

Pluto

Uranus

Jupiter

Mars

Earth

Mercury

Neptune Venus

Saturn

°F

°C

WWW.ASTRONOMY.COM 17

The shape of the Milky Way, usually pictured

as a flat spiral, may actually be more akin to

a warped and twisted disk, according to a

new study published February 4 in Nature

Astronomy. The study analyzed 1,339 stars

whose distances could be determined with

great accuracy.

Each star in the study is a Cepheid vari-

able, a type of pulsating star whose intrinsic

brightness is tied to how long it takes to oscil-

late between bright and dim. Normally, it’s

difficult to tell if a star is bright and far away

or dim and nearby. Because a Cepheid’s

period tells astronomers how bright the star

truly is, by comparing that number with how

bright it appears, researchers can accurately

pin down its distance.

Using infrared data from the Wide-field

Infrared Survey Explorer, astronomers from

Macquarie University in Australia and the

Chinese Academy of Sciences determined

the distance to each Cepheid in their data set

to an accuracy of 5 percent or better. They

then plotted these distances in 3D, creating

a new map of the Milky Way that shows the

galaxy’s disk has a distinct kink.

Astronomers had known about a kink in

our galaxy’s gas disk, but they didn’t know

that the stars would follow the same shape.

The new data also suggest that the warp in

the Milky Way’s disk precesses, or spins, like

a top. “The twisting of the warp is new,”

astronomer and study co-author Richard

deGrijs of Macquarie University told

Astronomy. “It’s been seen in a dozen other

galaxies before, but not ours.”

The authors hypothesize that as the Milky

Way’s inner disk of stars rotates, it produces

drag on the outer disk as well, distorting the

flat spiral. — K.H.

The Milky Way has a galactic twist

FROM HOT TO COLD

PLANETARY TEMPS. Although many planets (and dwarf planets) have temperatures that

vary drastically, as a general rule of thumb, the average temperature of a planet drops as you

go farther from the Sun. Venus, however, is the exception. Even though Mercury is the closest

planet to the Sun, Venus, at more than 850 degrees Fahrenheit (450 degrees Celsius), has the

highest average temperature of any planet in the solar system. Unlike Mercury, which has a

very thin atmosphere and slow rotation rate, Venus has an incredibly dense, heat-trapping

atmosphere that perpetuates the global greenhouse effect. — J.P.

Not often do two spacecraft get to say hello to

each other. But NASA’s Lunar Reconnaissance

Orbiter (LRO) and the China National Space

Administration’s Chang’e-4 have had the chance

several times.

In early February, LRO spied the Chang’e-

lander and its Yutu-2 rover on the farside of the

Moon from an altitude of 51 miles (82 kilome-

ters). At the time, the rover had already traveled

95 feet (29 m) northwest of the lander, though it

has gone even farther since then.

Sitting in Von Kármán Crater, the Chinese mis-

sion will study the Moon’s topography, explore

what lies beneath its surface, and record the

composition of the crater’s rocks. Researchers

hope this information will reveal more about

how the Moon’s farside differs from the nearside

we see from Earth. — A.J., A.K.

Hello there, Chang’e-

The funding awarded by the National Science Foundation to

Caltech and MIT to upgrade LIGO by 2024, allowing scientists

$20,400,000 to search a greater volume of space for gravitational waves.

WARPED DISK. The Milky Way’s disk has a distinctive twist — exaggerated here for illustrative purposes.

NEWLY NAMED. The International Astronomical Union approved the name Statio Tianhe, which is derived from the

ancient Chinese term for Milky Way, for the landing site of the Chang’e-4 lander currently studying the Moon’s farside.

FAST

FAC T

The dayside temperature of Mercury

reaches about 800 degrees Fahrenheit,

while the nightside temperature drops

as low as –290 F (–180 C), about as cold as

the ice giants Uranus and Neptune.

CHAO LIU, NATIONAL ASTRONOMICAL OBSERVATORIES, CHINESE ACADEMY OF SCIENCES

NASA/GSFC/ARIZONA STATE UNIVERSITY

PASSING BY. This image on February 1 from the Lunar

Reconnaissance Orbiter shows the Chang’e-4 lander

(vertical arrow) and its rover, Yutu-2 (horizontal arrow).

ASTRONOMY

: ROEN KELLY