OBSERVING
Celestial Calendar
52 July 2014 sky & telescope
The Closing of 44 Boötis
Can your scope separate a double star 1 arcsecond wide? At high
power, a 4-inch scope with excellent optics ought to do it during
excellent seeing. A lovely test pair this year is 44 Boötis, an inter-
esting 5th-magnitude binary off the handle-end of the Big Dipper.
The brighter of 44 Boo’s two components is a very Sun-like
star of magnitude 5.3, spectral type G0V. The secondary star is
an eclipsing binary of the W Ursae Majoris type: a peanut-shaped
contact binary that varies continuously from about magnitude
5.8 to 6.4, with two almost-equal eclipses during each 6.427-hour
orbital cycle. That’s fast enough to create a subtle change in the
binary’s appearance in the course of an observing session if your
timing is lucky. At a distance of 42 light-years, 44 Boo B is the
nearest contact binary star to the solar system.
The A-B pair is currently passing through an exciting part
of its 210-year orbit: the stars are rapidly closing year by year. A
recent orbit calculation by Henry Zirm in Jena, Germany, puts the
stars’ separation at 1.06′′ this July 1st and 1.03′′ by September 15th.
They’ll reach a minimum separation of 0.23′′ in 2020.
The secondary is currently east-northeast of the primary (at
position angle 66°°) but will swing around to the primary’s south-
west in the next decade. The table below gives the pair’s predicted
separation and position angle, according to Zirm’s orbit, around
the beginning and end of summer for the next 10 years. Position
angle is counted from north (0°) through east (90°), south (180°),
and west (270°).
Keep the table handy as 44 Boo becomes a challenge object for
bigger and bigger telescopes.
Bonus binary: OΣ 291 .The asterism to catch for fi nding 44
Boo is a little arc of three stars, 1.2° long, with 44 Boo in the mid-
dle, as shown on the map. The star southwest of 44 Boo (by^2 / 3 °)is
an utterly diff erent visual double, much wider. It’s OΣ 291, separa-
tion 35′′, magnitudes 6.3 and 9.6, with a slight color contrast. ✦
Orbit (^) o
f (^) B
A
2021
1 ̋
1 ̋
1 ̋ 2 ̋ 3 ̋ 4 ̋
2 ̋
3 ̋
2014
44 Boötis AB
OΣ 291
W R
R
RX
τ
12
α
κ
λ
ι
θ
ρ
γ
σ
33
ε
ξ
38
39
ω
β
ψ
44
47
χ
δ
μ
ζ
81
8483
η
86
Mizar
Alkaid
Izar
5466 M3
M51
M101
Arcturus
BOÖTES
CANES
VENATICI
UMA
DRACO
15 h 30 m 15 h 00 m 14 h 30 m 14 h 00 m 13 h 30 m
+40°
+35°
+30°
+25°
+20°
+45°
+50°
Star magnitudes
1 2 3 4 5 6
Above: North of the head of Boötes, east of Alkaid at the end of the Big Dipper’s handle, lies
a little curved row of three stars, including the doubles 44 Boötis and OΣ 291, tight and wide,
respectively. This chart shows stars to magnitude 6.5. Below left: Double-star enthusiast John
Nanson of Oregon drew 44 Boo as seen with a 4-inch f/13 refractor at 173×, when the pair’s
separation was 1.35′′ in April 2012. At 250× he could make out a thread of black sky between the
two. Below right: The apparent orbit 44 Boötis B relative to the brighter component A, as seen
projected on the sky. The true orbit is tipped far out of the paper, only 6° from our line of sight.
2014 1.06′′ 66 ° 1.03′′ 67 °
2015 0.91′′ 68 ° 0.88′′ 69 °
2016 0.76′′ 72 ° 0.73′′ 73 °
2017 0.61′′ 77 ° 0.58′′ 79 °
2018 0.46′′ 84 ° 0.43′′ 87 °
2019 0.33′′ 100 ° 0.30′′ 104 °
2020 0.24′′ 130 ° 0.23′′ 138 °
2021 0.25′′ 170 ° 0.27′′ 176 °
2022 0.36′′ 196 ° 0.38 ′′ 199 °
2023 0.50′′ 208 ° 0.53′′ 210 °
2024 0.65′′ 215 ° 0.68′′ 216 °
1.06′′
0 .91′′
0 .7 6 ′′
0.61′′
0 .46′′
0 .3 3 ′′
0.24′′
0 .2 5 ′′
0 .3 6 ′′
0.50′′
0 .6 5 ′′
66 °°
68 °°
72 °°
77 °°
84 °°
100 °°
130 °°
170 °°
196 °°
208 °°
215 °°
67 °°
69 °°
73 °°
79 °°
87 °°
104 °°
138 °°
176 °°
199 °°
210 °°
216 °°
1.03′′
0. 88 ′′
0 .73′′
0.5 8 ′′
0 .43′′
0 .3 0 ′′
0.23′′
0 .27′′
0.3 8 ′′
0.53′′
0 .6 8 ′′
44 Boötis AB
July 1 Sept. 15
Year Sep. P.A. Sep. P.A.
For the Moon’s librations in July, see: skypub.com/july2014librations.