Sky & Telescope - April 2023 - 40

HUBBLE HERITAGE TEAM (AURA / STSCI / NASA)
Novae
magnitude +1.3; and finally Nova Puppis 1942, climbing to
magnitude +0.5.
And the 80-plus years since? Nothing at all: The brightest
blast was second-magnitude Nova Cygni 1975. " That's a scandal, "
says Bradley Schaefer (Louisiana State University). He
thinks those bright novae are still appearing in our sky. " No
one spots them! It's horrifying. "
Schaefer blames a shift in observing habits. Starting
around 1890, talented amateur astronomers made a sport of
finding novae. These observers memorized the naked-eye stars
and searched the sky for new ones. After World War II, warsurplus
binoculars flooded the country, giving amateurs the
chance to find fainter and farther novae. But because distant
novae congregate in the band of the Milky Way, that's where
amateurs conducted their searches. As a result, he says, the
brightest and nearest novae, outside that band, were missed.
Increasing light pollution has only exacerbated the problem
by masking novae as they brighten and fade.
But Shafter is skeptical of this claim, saying the disparIN
A CROWD Novae have even erupted in star clusters - specifically
in globular clusters, which are some of the most ancient denizens of our
galaxy. (Most open clusters are too young for novae.) In 1860 observers
saw a nova in M80 (above), a globular cluster in Scorpius. A second
nova, in 1938, appeared in M14 in Ophiuchus, but astronomers spotted
that blast only decades later by examining old photographic plates.
assumed in the 1970s when predicting that novae contribute
significant amounts of lithium to the galaxy. In contrast,
supernovae occur in the Milky Way perhaps twice a century.
So nova explosions happen 1,000 to 2,000 times more often
than supernovae.
Where Have All the Bright Novae Gone?
However, a specter haunts these calculations: Bright novae
seem to have vanished.
During the first half of the 20th century, a nova peaked
at first magnitude or brighter each decade. The first, Nova
Persei 1901, hit magnitude +0.2 and rivaled Rigel in brightness.
Next came the brightest nova ever known, Nova Aquilae
1918, which attained magnitude -1.1 and almost surpassed
Sirius. The following decades featured Nova Pictoris 1925,
reaching magnitude +1.0; Nova Herculis 1934, peaking at
ity is " probably just due to small-number statistics. " In 2017
he calculated that the difference between the earlier era and
the modern one has a 10% chance of being a statistical fluke.
That's about the same chance you can flip a fair coin and get
heads three times in a row. Most scientists consider such a
significance level suggestive but not definitive.
Schaefer calculates the odds differently: " It's significant
past the 3-sigma level, " which means a 0.3% significance level
- equivalent to getting eight or nine heads in a row. " That's
not a fluke. " He says modern observers fail to find about half
of the brightest novae.
But Starrfield can't believe amateur astronomers would
miss novae as bright as first or second magnitude. " These
guys really know the sky, " he says. " I don't know the sky at
all; I mean, I'm lucky to find Jupiter. "
Whatever the case, someday - or, more precisely, some
night - the next bright nova will shine. Why not be the one
who finds it? Scanning the whole sky with the naked eye
before peering through a scope might yield that long-overdue
bright nova - and you'll make astronomical history.
¢ KEN CROSWELL has neither a cell phone nor a car, but he
does like nucleosynthesis.
All Known Novae of First Magnitude and Brighter from 1900 to 2022
Name
Nova Persei 1901
Nova Aquilae 1918
Nova Pictoris 1925
Nova Herculis 1934
Nova Puppis 1942
40 APRIL 2023 * SKY & TELESCOPE
Variable-Star Name
GK Persei
V603 Aquilae
RR Pictoris
DQ Herculis
CP Puppis
Brightest Apparent Mag(v)
+0.2
−1.1
+1.0
+1.3
+0.5
Distance (ly)
1,420
1,060
1,630
1,620
2,550
Orbital Period (d)
2.0
0.14
0.15
0.19
0.06
Sky & Telescope - April 2023

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