Sky & Telescope - October 2019 - 15

had reason to complain: Gravity behaves in such a complex
way that, with the exception of the most trivial situations,
we cannot simply look at a galaxy now and predict precisely
what it looked like at a previous time - Humpty Dumpty can
never be put back together again.
But although we cannot yet reconstruct our galaxy's past
this way, it turns out that with a little ingenuity, we can sidestep the impossibilities and truly turn back the gravitational
clock in an attempt to map our galaxy's neighborhood.

Nature vs. Nurture

Milky Way

One of the most fundamental questions in cosmology is how
galaxies form and grow into the magnificent objects we see
today. Just as with children, the answer is not merely a matter of genes; it's also one of environment. Our home galaxy,
the Milky Way, lives very close to its sibling, the Andromeda
Galaxy, and a smattering of smaller dwarf galaxies. This
neighborhood of galaxies (which we call the Local Group) lies
off the edge of the Virgo Cluster, a metropolis of some 2,000
galaxies about 50 million light-years away. In the opposite
direction, a void abuts our location. Together with these and
other clusters and voids, we are part of a vast, watershed-like
conglomeration of galaxies that forms our cosmic nation.
To understand what made the Milky Way turn out the way
it ultimately did, with its large spiral disk and rich collection

30

Distance
(million light-years)

ALFAZOA J1952+1428

KK 246

The Local Void

M83

Milky Way

M81

Maffei 2
Maffei 1

p COSMIC FLOWS Each sphere in this wide-angle perspective represents a galaxy in the nearby universe. Arrows indicate the streamlines
the galaxies follow, and colors correspond to a region's density (red for
dense clusters, blue for voids).

Distance
(million light-years)

Centaurus A

Andromeda
IC 342
NGC 253

-20
Dist
a
(m nce
ligh illion
t-ye
ars)

LE AH TISCIONE / S&T, SOURCE: DA NIEL
POM ARÈDE (CE A UNIVERSITÉ PA RIS-SACL AY )

0

His school of thought produced some of the greatest lumi0
naries in modern astrophysics, a number of whom are still
active today, mostly spread across the Western world in a
-450
post-Soviet diaspora.
-450
0
20
SGX (km/s)
The voice berating our method came from Andrei Doroshp LOCAL SHEET Seen in supergalactic coordinates, the Milky Way and
kevich - a scion in the field who, now at more than 80 years
its largest neighbors (labeled) occupy the Local Sheet, which abuts the
of age, is one of the last of Zeldovich's living disciples. He
Local Void. Circles mark 6.5 million, 13 million, and 20 million light-years.
sk yandtele scope.com * OCTOBE R 2 019

15



http://www.skyandtelescope.com

Sky & Telescope - October 2019

Table of Contents for the Digital Edition of Sky & Telescope - October 2019

Contents
Sky & Telescope - October 2019 - Cover1
Sky & Telescope - October 2019 - Cover2
Sky & Telescope - October 2019 - 1
Sky & Telescope - October 2019 - Contents
Sky & Telescope - October 2019 - 3
Sky & Telescope - October 2019 - 4
Sky & Telescope - October 2019 - 5
Sky & Telescope - October 2019 - 6
Sky & Telescope - October 2019 - 7
Sky & Telescope - October 2019 - 8
Sky & Telescope - October 2019 - 9
Sky & Telescope - October 2019 - 10
Sky & Telescope - October 2019 - 11
Sky & Telescope - October 2019 - 12
Sky & Telescope - October 2019 - 13
Sky & Telescope - October 2019 - 14
Sky & Telescope - October 2019 - 15
Sky & Telescope - October 2019 - 16
Sky & Telescope - October 2019 - 17
Sky & Telescope - October 2019 - 18
Sky & Telescope - October 2019 - 19
Sky & Telescope - October 2019 - 20
Sky & Telescope - October 2019 - 21
Sky & Telescope - October 2019 - 22
Sky & Telescope - October 2019 - 23
Sky & Telescope - October 2019 - 24
Sky & Telescope - October 2019 - 25
Sky & Telescope - October 2019 - 26
Sky & Telescope - October 2019 - 27
Sky & Telescope - October 2019 - 28
Sky & Telescope - October 2019 - 29
Sky & Telescope - October 2019 - 30
Sky & Telescope - October 2019 - 31
Sky & Telescope - October 2019 - 32
Sky & Telescope - October 2019 - 33
Sky & Telescope - October 2019 - 34
Sky & Telescope - October 2019 - 35
Sky & Telescope - October 2019 - 36
Sky & Telescope - October 2019 - 37
Sky & Telescope - October 2019 - 38
Sky & Telescope - October 2019 - 39
Sky & Telescope - October 2019 - 40
Sky & Telescope - October 2019 - 41
Sky & Telescope - October 2019 - 42
Sky & Telescope - October 2019 - 43
Sky & Telescope - October 2019 - 44
Sky & Telescope - October 2019 - 45
Sky & Telescope - October 2019 - 46
Sky & Telescope - October 2019 - 47
Sky & Telescope - October 2019 - 48
Sky & Telescope - October 2019 - 49
Sky & Telescope - October 2019 - 50
Sky & Telescope - October 2019 - 51
Sky & Telescope - October 2019 - 52
Sky & Telescope - October 2019 - 53
Sky & Telescope - October 2019 - 54
Sky & Telescope - October 2019 - 55
Sky & Telescope - October 2019 - 56
Sky & Telescope - October 2019 - 57
Sky & Telescope - October 2019 - 58
Sky & Telescope - October 2019 - 59
Sky & Telescope - October 2019 - 60
Sky & Telescope - October 2019 - 61
Sky & Telescope - October 2019 - 62
Sky & Telescope - October 2019 - 63
Sky & Telescope - October 2019 - 64
Sky & Telescope - October 2019 - 65
Sky & Telescope - October 2019 - 66
Sky & Telescope - October 2019 - 67
Sky & Telescope - October 2019 - 68
Sky & Telescope - October 2019 - 69
Sky & Telescope - October 2019 - 70
Sky & Telescope - October 2019 - 71
Sky & Telescope - October 2019 - 72
Sky & Telescope - October 2019 - 73
Sky & Telescope - October 2019 - 74
Sky & Telescope - October 2019 - 75
Sky & Telescope - October 2019 - 76
Sky & Telescope - October 2019 - 77
Sky & Telescope - October 2019 - 78
Sky & Telescope - October 2019 - 79
Sky & Telescope - October 2019 - 80
Sky & Telescope - October 2019 - 81
Sky & Telescope - October 2019 - 82
Sky & Telescope - October 2019 - 83
Sky & Telescope - October 2019 - 84
Sky & Telescope - October 2019 - Cover3
Sky & Telescope - October 2019 - Cover4
https://www.nxtbook.com/nxtbooks/aas/st_202406
https://www.nxtbook.com/nxtbooks/aas/st_202405
https://www.nxtbook.com/nxtbooks/aas/st_202404_qr
https://www.nxtbook.com/nxtbooks/aas/st_202404
https://www.nxtbook.com/nxtbooks/aas/st_202403
https://www.nxtbook.com/nxtbooks/aas/st_202402
https://www.nxtbook.com/nxtbooks/aas/st_202401_aus
https://www.nxtbook.com/nxtbooks/aas/st_202401
https://www.nxtbook.com/nxtbooks/aas/st_202312_aus
https://www.nxtbook.com/nxtbooks/aas/st_202312
https://www.nxtbook.com/nxtbooks/aas/st_202311
https://www.nxtbook.com/nxtbooks/aas/st_202310
https://www.nxtbook.com/nxtbooks/aas/st_202309
https://www.nxtbook.com/nxtbooks/aas/st_202308
https://www.nxtbook.com/nxtbooks/aas/st_202307
https://www.nxtbook.com/nxtbooks/aas/st_202306
https://www.nxtbook.com/nxtbooks/aas/st_202305
https://www.nxtbook.com/nxtbooks/aas/st_202304
https://www.nxtbook.com/nxtbooks/aas/st_202304_qr
https://www.nxtbook.com/nxtbooks/aas/st_202303
https://www.nxtbook.com/nxtbooks/aas/st_202302
https://www.nxtbook.com/nxtbooks/aas/st_202301
https://www.nxtbook.com/nxtbooks/aas/st_202212
https://www.nxtbook.com/nxtbooks/aas/st_202211
https://www.nxtbook.com/nxtbooks/aas/st_202210
https://www.nxtbook.com/nxtbooks/aas/st_202209
https://www.nxtbook.com/nxtbooks/aas/st_202208
https://www.nxtbook.com/nxtbooks/aas/st_202207
https://www.nxtbook.com/nxtbooks/aas/st_202206
https://www.nxtbook.com/nxtbooks/aas/st_202205
https://www.nxtbook.com/nxtbooks/aas/st_202204
https://www.nxtbook.com/nxtbooks/aas/st_202203
https://www.nxtbook.com/nxtbooks/aas/st_202202
https://www.nxtbook.com/nxtbooks/aas/st_202201
https://www.nxtbook.com/nxtbooks/aas/st_202112
https://www.nxtbook.com/nxtbooks/aas/st_202111
https://www.nxtbook.com/nxtbooks/aas/st_202110
https://www.nxtbook.com/nxtbooks/aas/st_202109
https://www.nxtbook.com/nxtbooks/aas/st_202108
https://www.nxtbook.com/nxtbooks/aas/st_202107
https://www.nxtbook.com/nxtbooks/aas/st_202106
https://www.nxtbook.com/nxtbooks/aas/st_202105
https://www.nxtbook.com/nxtbooks/aas/st_202104
https://www.nxtbook.com/nxtbooks/aas/st_202103
https://www.nxtbook.com/nxtbooks/aas/st_202102
https://www.nxtbook.com/nxtbooks/aas/st_202101
https://www.nxtbook.com/nxtbooks/aas/skywatch_2021
https://www.nxtbook.com/nxtbooks/aas/st_202012
https://www.nxtbook.com/nxtbooks/aas/st_202011
https://www.nxtbook.com/nxtbooks/aas/st_202010
https://www.nxtbook.com/nxtbooks/aas/st_202009
https://www.nxtbook.com/nxtbooks/aas/st_202008
https://www.nxtbook.com/nxtbooks/aas/st_202007
https://www.nxtbook.com/nxtbooks/aas/st_202006
https://www.nxtbook.com/nxtbooks/aas/st_202005
https://www.nxtbook.com/nxtbooks/aas/st_202004
https://www.nxtbook.com/nxtbooks/aas/st_202003
https://www.nxtbook.com/nxtbooks/aas/st_202002
https://www.nxtbook.com/nxtbooks/aas/st_202001
https://www.nxtbook.com/nxtbooks/aas/st_201912
https://www.nxtbook.com/nxtbooks/aas/st_201911
https://www.nxtbook.com/nxtbooks/aas/st_201910
https://www.nxtbook.com/nxtbooks/aas/st_201909
https://www.nxtbook.com/nxtbooks/aas/st_201908
https://www.nxtbook.com/nxtbooks/aas/st_201907
https://www.nxtbook.com/nxtbooks/aas/st_201906
https://www.nxtbook.com/nxtbooks/aas/st_201905
https://www.nxtbook.com/nxtbooks/aas/st_201904
https://www.nxtbook.com/nxtbooks/aas/st_201903
https://www.nxtbook.com/nxtbooks/aas/st_201902
https://www.nxtbook.com/nxtbooks/aas/st_201901
https://www.nxtbook.com/nxtbooks/aas/st_201812
https://www.nxtbook.com/nxtbooks/aas/st_201811
https://www.nxtbook.com/nxtbooks/aas/st_201810
https://www.nxtbook.com/nxtbooks/aas/st_201809
https://www.nxtbook.com/nxtbooks/aas/st_201808
https://www.nxtbook.com/nxtbooks/aas/st_201807
https://www.nxtbook.com/nxtbooks/aas/st_201806
https://www.nxtbook.com/nxtbooks/aas/st_201805
https://www.nxtbook.com/nxtbooks/aas/st_201804
https://www.nxtbook.com/nxtbooks/aas/st_201803
https://www.nxtbook.com/nxtbooks/aas/st_201802
https://www.nxtbook.com/nxtbooks/aas/st_201801
https://www.nxtbook.com/nxtbooks/aas/st_201712
https://www.nxtbook.com/nxtbooks/aas/st_201711
https://www.nxtbook.com/nxtbooks/aas/st_201710
https://www.nxtbook.com/nxtbooks/aas/st_201709
https://www.nxtbook.com/nxtbooks/aas/st_201708
https://www.nxtbook.com/nxtbooks/aas/st_201707
https://www.nxtbook.com/nxtbooks/aas/st_201706
https://www.nxtbook.com/nxtbooks/aas/st_201705
https://www.nxtbook.com/nxtbooks/aas/st_201704
https://www.nxtbook.com/nxtbooks/aas/st_201703
https://www.nxtbook.com/nxtbooks/aas/st_201702
https://www.nxtbook.com/nxtbooks/aas/st_201701
https://www.nxtbook.com/nxtbooks/aas/st_201612
https://www.nxtbook.com/nxtbooks/aas/st_201611
https://www.nxtbook.com/nxtbooks/aas/st_201610
https://www.nxtbook.com/nxtbooks/aas/st_201609
https://www.nxtbook.com/nxtbooks/aas/st_201608
https://www.nxtbook.com/nxtbooks/aas/st_201607
https://www.nxtbook.com/nxtbooks/aas/st_201606
https://www.nxtbook.com/nxtbooks/aas/st_201605
https://www.nxtbook.com/nxtbooks/aas/st_201604
https://www.nxtbook.com/nxtbooks/aas/st_201603
https://www.nxtbook.com/nxtbooks/aas/st_201602
https://www.nxtbook.com/nxtbooks/aas/st_201601
https://www.nxtbook.com/nxtbooks/aas/st_201512
https://www.nxtbook.com/nxtbooks/aas/st_201511
https://www.nxtbook.com/nxtbooks/aas/st_201510
https://www.nxtbook.com/nxtbooks/aas/st_201509
https://www.nxtbook.com/nxtbooks/aas/st_201508
https://www.nxtbook.com/nxtbooks/aas/st_201507
https://www.nxtbook.com/nxtbooks/aas/st_201506
https://www.nxtbook.com/nxtbooks/aas/st_201505
https://www.nxtbook.com/nxtbooks/aas/st_201504
https://www.nxtbook.com/nxtbooks/aas/st_201503
https://www.nxtbook.com/nxtbooks/aas/st_201502
https://www.nxtbook.com/nxtbooks/aas/st_201501
https://www.nxtbook.com/nxtbooks/aas/st_201412
https://www.nxtbook.com/nxtbooks/aas/st_201411
https://www.nxtbook.com/nxtbooks/aas/st_201410
https://www.nxtbook.com/nxtbooks/aas/st_201409
https://www.nxtbook.com/nxtbooks/aas/st_201408
https://www.nxtbook.com/nxtbooks/aas/st_201407
https://www.nxtbook.com/nxtbooks/aas/st_201406
https://www.nxtbook.com/nxtbooks/aas/st_mars
https://www.nxtbook.com/nxtbooks/aas/st_201405
https://www.nxtbook.com/nxtbooks/aas/st_201404
https://www.nxtbook.com/nxtbooks/aas/st_201403
https://www.nxtbook.com/nxtbooks/aas/st_201402
https://www.nxtbook.com/nxtbooks/aas/st_201401
https://www.nxtbook.com/nxtbooks/aas/st_201312
https://www.nxtbook.com/nxtbooks/aas/st_201311
https://www.nxtbook.com/nxtbooks/aas/st_201310
https://www.nxtbook.com/nxtbooks/aas/st_201309
https://www.nxtbook.com/nxtbooks/aas/st_201308
https://www.nxtbook.com/nxtbooks/aas/st_201307
https://www.nxtbook.com/nxtbooks/aas/st_201306
https://www.nxtbook.com/nxtbooks/aas/st_201305
https://www.nxtbook.com/nxtbooks/aas/st_201304
https://www.nxtbook.com/nxtbooks/aas/st_201303
https://www.nxtbook.com/nxtbooks/aas/st_201302
https://www.nxtbook.com/nxtbooks/aas/st_201301
https://www.nxtbook.com/nxtbooks/aas/st_201212
https://www.nxtbook.com/nxtbooks/aas/st_201211
https://www.nxtbook.com/nxtbooks/aas/st_201210
https://www.nxtbook.com/nxtbooks/aas/st_201209
https://www.nxtbook.com/nxtbooks/aas/st_201208
https://www.nxtbook.com/nxtbooks/aas/st_201207
https://www.nxtbook.com/nxtbooks/aas/st_201206
https://www.nxtbook.com/nxtbooks/aas/st_201205
https://www.nxtbook.com/nxtbooks/aas/st_201204
https://www.nxtbook.com/nxtbooks/aas/st_201203
https://www.nxtbook.com/nxtbooks/aas/st_201202
https://www.nxtbook.com/nxtbooks/aas/st_201201
https://www.nxtbook.com/nxtbooks/aas/st_201112
https://www.nxtbook.com/nxtbooks/aas/st_201111
https://www.nxtbook.com/nxtbooks/aas/st_201110
https://www.nxtbook.com/nxtbooks/aas/st_201109
https://www.nxtbook.com/nxtbooks/aas/st_201108
https://www.nxtbook.com/nxtbooks/aas/st_201107
https://www.nxtbook.com/nxtbooks/aas/st_201106
https://www.nxtbook.com/nxtbooks/aas/st_201105
https://www.nxtbook.com/nxtbooks/aas/st_201104
https://www.nxtbook.com/nxtbooks/aas/st_201103
https://www.nxtbook.com/nxtbooks/aas/st_201102
https://www.nxtbook.com/nxtbooks/aas/st_201101
https://www.nxtbook.com/nxtbooks/aas/st_201012
https://www.nxtbook.com/nxtbooks/aas/st_201011
https://www.nxtbook.com/nxtbooks/aas/st_201010
https://www.nxtbook.com/nxtbooks/aas/st_201009
https://www.nxtbook.com/nxtbooks/aas/st_201008
https://www.nxtbook.com/nxtbooks/aas/st_201007
https://www.nxtbook.com/nxtbooks/aas/st_201006
https://www.nxtbook.com/nxtbooks/aas/st_201005
https://www.nxtbook.com/nxtbooks/aas/st_201004
https://www.nxtbook.com/nxtbooks/aas/st_201003
https://www.nxtbook.com/nxtbooks/aas/st_201002
https://www.nxtbook.com/nxtbooks/aas/st_201001
https://www.nxtbookmedia.com