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Old February 26th 06, 02:08 AM posted to sci.astro.amateur
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Default 145 CMa - the Winter Albireo - a colorful after-work winter double Feb-Mar

145 CMa (HD056577) - the Winter Albireo - is at it's most favorable low
declination position (J071636.00-231912.0) for 41N op's. 145 CMa is
visible in small refractors after sunset from urban light polluted
skies. The Belmont Society Colorful Double Star List describes pi Gem
as "orange/blue-green" while Mullaney's _Celestial Harvest_ gives this
double an effusive recommendaton. The primary of this colorful
multiple is a v4.8 K4III star at an estimated distance of 536 parsecs.
The discover designation - HJ 3945 - attributes first recorded sighting
to William Herschel. At 536 parsecs and G236.50-05.22, this double
sits west of Canis Major "down-wind" in the Orion Arm from Sol, in a
area rich in small open clusters.

Current (Epoch 2000) CCDM data on 145 CMa (CCDM 07166-2319) is:

C PA sep mag
A 4.8
B 055 26.6 6.8

145 CMa is about 3 degs east of omi2 CMa. A courtesy star hopping
finder chart is provided at:
http://members.csolutions.net/fisher...45StarHops.jpg

145 CMa current is low on the horizon from 41N ops - at about only 20
degrees in altitude at sunset. 145 CMa can be star-hopped or
right-angle swept by starting at omi2 CMa. From my light polluted v3.0
urban skies, I began at del CMa and swept north about 3 degs to omi2
CMa. omi2 CMa was just barely naked-eye visible in the light pollution.
Due to light pollution, there were really not any good landmarks to
star hop to 145 CMa. Finding this double is a bit challenging in light
polluted skies. Since 145 CMa is a direct east declination sweep from
omi2 CMa, I simply used the lowest feasible magnification, with the
largest TFOV, about 1 deg in this case - and then counted about 3 1/2
ep views east of omi2 CMa until I saw a small double that looked like
145's namesake - Albireo.

In a small alt-az 60mm refractor under urban Bortle class 8 mag 3.0
light-polluted urban skies at 22x, 145 CMa lives up to its namesake as
the Winter Albireo. It is a nice, distinct, intense blue-gold pair
about 22" apart. But unlike it's summer namesake, the Winter Albireo
is over 500 parsecs distant, while the "real" Albireo is about 125
parsecs away. On increasing magnification to about 78x, the Winter
Albireo the colors fade and somewhat dim in a small refractor. In
contrast, the bet Cyg double retains is golden-jewel crispness under
higher magnification.

All-in-all, this was a nice 15-20 minutes of easy after-work
beer-in-hand viewing at 41N.

The Belmont Society Colorful Double Star list can be found at:
http://www.belmontnc.4dw.net/dblstrs.htm

- Canopus56