2019-12-01_Astronomy

8 ASTRONOMY • DECEMBER 2019

ASTRO LETTERS

Globular clusters, tackled

Great article in the August issue

of Astronomy magazine on globu-

lar star clusters. As a professional

and amateur astronomer for

over 40 years, I have viewed and

studied globular clusters exten-

sively. I recently retired from the

University of Hawai‘i but still

maintain an observatory on Kaua‘i. I have seen all of

the globular clusters you discussed, except 47 Tucanae,

which doesn’t come above the horizon from Hawai‘i.

— James Dire, Peoria, IL

Solving mysteries

Astronomers have relentlessly searched the skies, and

the result is a multitude of surprising images that

dazzle us, giving us some answers, but not all. Your

articles by renowned astronomers, astrophysicists, and

observers are mind-blowing. The July special issue on

the Apollo 11 Moon landing was nostalgic since I saw

it on TV. We’ve come a long way since then. Thank

you, Astronomy magazine, for the May and July issues.

Can’t wait to see the next mystery solved. — Shoba

Kaicker, Toronto, Ontario

The coming smackdown

On page 11 in your June issue under your Quick Takes

section, you write, “According to data from the Gaia sat-

ellite, the Milky Way will collide with the Andromeda

Galaxy in some 3.9 billion years, not 4.5 billion years as

previously thought.”

Well, I think you guys have that backwards from my

reading of a February 2019 paper by van der Marel et al.

titled “First Gaia Dynamics of the Andromeda System:

DR2 Proper Motions, Orbits, and Rotation of M31 and

M33.” In it, they write, “The MW and M31 are still des-

tined to merge. However, both the timing and the

impact parameter of the first encounter have increased

... from ... ~3.9 Gyr to ~4.5 Gyr ...” — Scott Harrington,

Evening Shade, AR

From the editors: Scott, you’re absolutely right — we

ended up saying things the wrong way around. What we

should have said was, “the Milky Way will collide with

the Andromeda Galaxy in some 4.5 billion years, not

3.9 billion years, as previously thought.”

NGC 362 is just one of
150 globular clusters
in the Milky Way
galaxy. NASA

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Festival

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