Sky and Telescope - June 2015 - 75

L

Complete your digital
Sky & Telescope library!

S&T: CRAIG MICHAEL UTTER

TH E

To determine the necessary size of your
secondary mirror, you need to know L. It is the
distance from the center of the tube to the focal
plane, where the eyepiece's ﬁeld stop is positioned when the telescope is focused at inﬁnity.

piece to drop ½ magnitude, we can use a
2.14-inch secondary - a full size smaller.
But what if our scope only has a 1¼-inch
focuser? Then we'd only need a 1.83-inch
secondary - two sizes smaller than the
½-inch rule suggests.
The key point in all this is that for any
given telescope, there is more than one
correct solution. You may, for example,
tolerate more (or less) edge-of-ﬁeld dimming. Or perhaps you're planning a scope
for imaging rather than visual use. In
general, it's better to err on the side of
choosing too big rather than too small.
But once you take into account the facts,
you can use your judgment to decide
which size best satisﬁes your needs. ✦

L
ETE
PLET
OMPLET COLL
OMPLETE
THE COMPLETE COLLE

$49.95

Item # THETELDVD

$49.95

Item # THESKYDVD

Before Sky & Telescope was created in 1941 there existed two separate publications:
The Telescope, published from 1933-1941, and The Sky, published from 1936-1941.
You now have the opportunity to own all 48 issues of The Telescope and all 60 issues
of The Sky, each on its own DVD-ROM for easy viewing, searching, and printing!

llections
uy the co .95 each
B
9
ly for $4
separate em together
or buy th 10%!
e
and sav

TH E

1936 -194
THE SKY:
LETE
1 THE COMP
COLL ECTI

Contributing editor Gary Seronik has additional information about secondary-mirror
sizing on his website, garyseronik.com.

9
9 36 - 1 94
KY: 1 93 6- 19 4 1
K
TH E SK Y: 19 3 6 -1TI41
LECT
LECT ON
LEC
OLLECTION

Item # SKTLCOMBO
MBO

Do you have a telescope or observing
accessory that S&T's readers would
enjoy knowing about? Get featured in
Telescope Workshop by e-mailing Gary
Seronik at gary@garyseronik.com.

ON

$89.95

94 1
9
3
93 6- 19 41
Y: 19 36 -1 IO
ECT
TH E SKLETE COLLECTION
MP
THE CO

Discover more at: www.shopatsky.com
To Order by Phone Call: 1-888-253-0230

http://www.garyseronik.com http://www.shopatsky.com http://www.shopatsky.com

Sky and Telescope - June 2015

Table of Contents for the Digital Edition of Sky and Telescope - June 2015

Contents
Sky and Telescope - June 2015 - Cover1
Sky and Telescope - June 2015 - Cover2
Sky and Telescope - June 2015 - 3
Sky and Telescope - June 2015 - Contents
Sky and Telescope - June 2015 - 5
Sky and Telescope - June 2015 - A
Sky and Telescope - June 2015 - B
Sky and Telescope - June 2015 - 6
Sky and Telescope - June 2015 - 7
Sky and Telescope - June 2015 - 8
Sky and Telescope - June 2015 - 9
Sky and Telescope - June 2015 - 10
Sky and Telescope - June 2015 - 11
Sky and Telescope - June 2015 - 12
Sky and Telescope - June 2015 - 13
Sky and Telescope - June 2015 - 14
Sky and Telescope - June 2015 - 15
Sky and Telescope - June 2015 - 16
Sky and Telescope - June 2015 - 17
Sky and Telescope - June 2015 - 18
Sky and Telescope - June 2015 - 19
Sky and Telescope - June 2015 - 20
Sky and Telescope - June 2015 - 21
Sky and Telescope - June 2015 - 22
Sky and Telescope - June 2015 - 23
Sky and Telescope - June 2015 - 24
Sky and Telescope - June 2015 - 25
Sky and Telescope - June 2015 - 26
Sky and Telescope - June 2015 - 27
Sky and Telescope - June 2015 - 28
Sky and Telescope - June 2015 - 29
Sky and Telescope - June 2015 - 30
Sky and Telescope - June 2015 - 31
Sky and Telescope - June 2015 - 32
Sky and Telescope - June 2015 - 33
Sky and Telescope - June 2015 - 34
Sky and Telescope - June 2015 - 35
Sky and Telescope - June 2015 - 36
Sky and Telescope - June 2015 - 37
Sky and Telescope - June 2015 - 38
Sky and Telescope - June 2015 - 39
Sky and Telescope - June 2015 - 40
Sky and Telescope - June 2015 - 41
Sky and Telescope - June 2015 - 42
Sky and Telescope - June 2015 - 43
Sky and Telescope - June 2015 - 44
Sky and Telescope - June 2015 - 45
Sky and Telescope - June 2015 - 46
Sky and Telescope - June 2015 - 47
Sky and Telescope - June 2015 - 48
Sky and Telescope - June 2015 - 49
Sky and Telescope - June 2015 - 50
Sky and Telescope - June 2015 - 51
Sky and Telescope - June 2015 - 52
Sky and Telescope - June 2015 - 53
Sky and Telescope - June 2015 - 54
Sky and Telescope - June 2015 - 55
Sky and Telescope - June 2015 - 56
Sky and Telescope - June 2015 - 57
Sky and Telescope - June 2015 - 58
Sky and Telescope - June 2015 - 59
Sky and Telescope - June 2015 - 60
Sky and Telescope - June 2015 - 61
Sky and Telescope - June 2015 - 62
Sky and Telescope - June 2015 - 63
Sky and Telescope - June 2015 - 64
Sky and Telescope - June 2015 - 65
Sky and Telescope - June 2015 - 66
Sky and Telescope - June 2015 - 67
Sky and Telescope - June 2015 - 68
Sky and Telescope - June 2015 - 69
Sky and Telescope - June 2015 - 70
Sky and Telescope - June 2015 - 71
Sky and Telescope - June 2015 - 72
Sky and Telescope - June 2015 - 73
Sky and Telescope - June 2015 - 74
Sky and Telescope - June 2015 - 75
Sky and Telescope - June 2015 - 76
Sky and Telescope - June 2015 - 77
Sky and Telescope - June 2015 - 78
Sky and Telescope - June 2015 - 79
Sky and Telescope - June 2015 - 80
Sky and Telescope - June 2015 - 81
Sky and Telescope - June 2015 - 82
Sky and Telescope - June 2015 - 83
Sky and Telescope - June 2015 - 84
Sky and Telescope - June 2015 - 85
Sky and Telescope - June 2015 - 86
Sky and Telescope - June 2015 - Cover3
Sky and Telescope - June 2015 - Cover4
https://www.nxtbook.com/nxtbooks/aas/st_202409
https://www.nxtbook.com/nxtbooks/aas/st_202408
https://www.nxtbook.com/nxtbooks/aas/st_202407
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