Sky & Telescope - February 2021 - 52

FEBRUARY 2021 OBSERVING
Exploring the Solar System by Charles Wood

Antoniadi
127 km

Copernicus
96 km

Aristarchus
40 km

A Lunar Main Sequence
Understanding lunar crater formation based on appearances.

I

H-R diagram. For example, one can
consider the main sequence of impact
craters as the systematic morphological
difference from small conical pits such
as the 13-km-diameter (8-mile) crater
Chladni, to mid-sized craters with
partial wall collapses as seen in 24-km
Lalande, and on to large craters with
terraced walls and central peaks, like
96-km Copernicus. Crater diameters
increase and morphology changes as
the size and/or velocity of the impac-

n astronomy, the main sequence is the
continuous band of stars spanning
the Hertzsprung-Russell diagram, which
plots stellar color and intrinsic brightness. When a large main-sequence star
runs out of hydrogen fuel, it becomes
cooler, redder, and radically expands in
size as it moves off of the main sequence.
Unlike stars, impact craters do not
dynamically evolve. But, based on size
and morphology, they often have parallels to the distribution of stars on the

2,400

S
Imbrium up
er
Basin
-g
ia
Nectaris
nt
s
Basin

1,000
600

Gi

an

Bailly
Proto-basin

Peak-ring basins

ts

Clavius

M

1E+24

230

Antoniadi
Copernicus

1E+22

ai

n-

se

1E+20

Complex-terraced craters

Aristarchus

qu

en

FEBRUARY 2 021 * SK Y & TELESCOPE

40

Lalande Complex-slump craters

ce

cr

at

15

Chladni

er

1E+18

Impact energy (kilojoules)

52

100

10

s

1E+16

Petit
Simple craters

1E+14

1E+12

Crater diameter (kilometers)

Grimaldi

Multi-ring basins

tors increase, delivering more energy
for fracturing, melting, excavation, and
ejecting lunar crustal rocks.
Crater-wall morphology stems from
how the impacted target rocks deform
as the initially excavated hole - the
transient cavity - becomes deeper and
wider. For small transient cavities, the
impacted rocks are strong enough to
withstand collapse into the resulting
depression, and a simple, conical crater
forms. With medium-sized transient
cavities, sections of the surrounding
walls collapse, creating complex-slump
craters. And for large cavities, the entire
surrounding wall slides into the hole,
creating complex-terraced craters. Rim
collapses significantly increase the crater's overall diameter. Central peak sizes
also change across the main sequence.
Simple craters don't have central peaks
at all because the pressure of the impact
didn't compress the subsurface rocks
sufficiently to cause a rebound. As the
impact energy increases, the compressed
target rocks rebound, transporting
deeper rocks to the surface to form a
central peak.
Inspired by the H-R diagram, I've
created a graph that tracks diameter and
morphology differences arising from
increasing impact energy. The horizontal axis represents the kinetic energy
produced by the impacting body, and the
vertical axis plots the resulting crater
diameter. I've also included approximate
transitional stages, from Simple to
Complex-slump craters at around 15-km
W The main sequence of lunar impact features
showing the relationship between morphology
and the energy required to create each

A LL PHOTOS: N ASA / GSFC / A RIZON A STATE
UNIV ERSIT Y; G R A PH: LE A H TISCIONE / S&T

Schrödinger
325 km



Sky & Telescope - February 2021

Table of Contents for the Digital Edition of Sky & Telescope - February 2021

Contents
Sky & Telescope - February 2021 - Cover1
Sky & Telescope - February 2021 - Cover2
Sky & Telescope - February 2021 - 1
Sky & Telescope - February 2021 - Contents
Sky & Telescope - February 2021 - 3
Sky & Telescope - February 2021 - 4
Sky & Telescope - February 2021 - 5
Sky & Telescope - February 2021 - 6
Sky & Telescope - February 2021 - 7
Sky & Telescope - February 2021 - 8
Sky & Telescope - February 2021 - 9
Sky & Telescope - February 2021 - 10
Sky & Telescope - February 2021 - 11
Sky & Telescope - February 2021 - 12
Sky & Telescope - February 2021 - 13
Sky & Telescope - February 2021 - 14
Sky & Telescope - February 2021 - 15
Sky & Telescope - February 2021 - 16
Sky & Telescope - February 2021 - 17
Sky & Telescope - February 2021 - 18
Sky & Telescope - February 2021 - 19
Sky & Telescope - February 2021 - 20
Sky & Telescope - February 2021 - 21
Sky & Telescope - February 2021 - 22
Sky & Telescope - February 2021 - 23
Sky & Telescope - February 2021 - 24
Sky & Telescope - February 2021 - 25
Sky & Telescope - February 2021 - 26
Sky & Telescope - February 2021 - 27
Sky & Telescope - February 2021 - 28
Sky & Telescope - February 2021 - 29
Sky & Telescope - February 2021 - 30
Sky & Telescope - February 2021 - 31
Sky & Telescope - February 2021 - 32
Sky & Telescope - February 2021 - 33
Sky & Telescope - February 2021 - 34
Sky & Telescope - February 2021 - 35
Sky & Telescope - February 2021 - 36
Sky & Telescope - February 2021 - 37
Sky & Telescope - February 2021 - 38
Sky & Telescope - February 2021 - 39
Sky & Telescope - February 2021 - 40
Sky & Telescope - February 2021 - 41
Sky & Telescope - February 2021 - 42
Sky & Telescope - February 2021 - 43
Sky & Telescope - February 2021 - 44
Sky & Telescope - February 2021 - 45
Sky & Telescope - February 2021 - 46
Sky & Telescope - February 2021 - 47
Sky & Telescope - February 2021 - 48
Sky & Telescope - February 2021 - 49
Sky & Telescope - February 2021 - 50
Sky & Telescope - February 2021 - 51
Sky & Telescope - February 2021 - 52
Sky & Telescope - February 2021 - 53
Sky & Telescope - February 2021 - 54
Sky & Telescope - February 2021 - 55
Sky & Telescope - February 2021 - 56
Sky & Telescope - February 2021 - 57
Sky & Telescope - February 2021 - 58
Sky & Telescope - February 2021 - 59
Sky & Telescope - February 2021 - 60
Sky & Telescope - February 2021 - 61
Sky & Telescope - February 2021 - 62
Sky & Telescope - February 2021 - 63
Sky & Telescope - February 2021 - 64
Sky & Telescope - February 2021 - 65
Sky & Telescope - February 2021 - 66
Sky & Telescope - February 2021 - 67
Sky & Telescope - February 2021 - 68
Sky & Telescope - February 2021 - 69
Sky & Telescope - February 2021 - 70
Sky & Telescope - February 2021 - 71
Sky & Telescope - February 2021 - 72
Sky & Telescope - February 2021 - 73
Sky & Telescope - February 2021 - 74
Sky & Telescope - February 2021 - 75
Sky & Telescope - February 2021 - 76
Sky & Telescope - February 2021 - 77
Sky & Telescope - February 2021 - 78
Sky & Telescope - February 2021 - 79
Sky & Telescope - February 2021 - 80
Sky & Telescope - February 2021 - 81
Sky & Telescope - February 2021 - 82
Sky & Telescope - February 2021 - 83
Sky & Telescope - February 2021 - 84
Sky & Telescope - February 2021 - Cover3
Sky & Telescope - February 2021 - Cover4
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