41N Observer: Transiting tonight notes

Based on a W118 op with objects transiting beginning 4:30 UTC through 6:00
UTC for North Am. observers

With the Moon now rising after 11:00 pm local time, the August dark-sky
frame has begun and continues through about August 27. Since the summer
orientation of the Milky Way is north to south in the local horizon system,
not suprisingly there are no transiting galaxies in this note. It's the
beginning of the season for the prime Milky Way galactic plane show starting
with the galactic core at the south horizon, Cygnus at the zenith and the
Perseus Double Cluster at the northeast end of the horizon.

I) In the 40 deg - 50 deg alt transit zone for 41N latitude

The start of this transit zone is 57 Aql and del Sct. 57 Aql(
J195438.40-081348.0) is a bright wide (35") double in Mullaney's celestial
harvest described as yellow and blue in color. 57 Aql is about 102 parsecs
distant. del Sct is a prototype star the class of delta Sct type pulsating
variables. At 4.71 mags, it is bright enough to use your Rainbow Optics
low-dispersion spectrometer on. More info on delta Sct at:
http://www.astro.uiuc.edu/~kaler/sow/deltasct.html
and in Kaler's classic book, Stars and their Spectra.

Three degrees below eta Aql, lies NGC6712 (Herschel 47-1, Clark534,
J185302.40-084218.0), a small (3') mag. 8.7 globular located 6.7 kpc
distant. This globular is unusual in that is a contradiction in
characteristics. Globulars are divided into two populations: the larger
group of clusters that are more metal-poor than (Fe/H) = -0.8 are
distributed in a spherical halo beyond 7kpc from the galactic core. The
smaller group of Clusters more metal-rich than (Fe/H) = -0.8 are distributed
in a disk system around and within the Milky Way galactic disk. NGC6712 is
less that 7kpc distant from the core, is near the plane of the Milky Way at
galactic latitude -4.3, but its metallicity [Fe/H] at -1.01 is less
than -0.8. NGC6712 lies near the metallicity border between old-halo and
young disk globular populations. The contradiction in characteristics is
probably just a case of fuzzy classification.
Zinn's 1985 paper on the two populations of globulars:
http://adsabs.harvard.edu/cgi-bin/np...pJ...293..424Z

Less than 1/2 degree from alf Sct, is mag. 7.8 open cluster (dia. 18')
NGC6664 (Herschel 12-8, J183640.80-081257.6). At 1.16 kpc distant, this
open cluster appears to be positioned in the Sagittarius-Carina Arm. At that
distance, its true physical size is estimated at about 6 parsecs.
Positionally, it is near Lynds large dark nebulae 616 and 617, which are not
optical objects for amateur class telescopes. Considering the density of
molecular clouds generally in the Aquilia Rift direction, it is a wonder
that any inter-arm open clusters can be seen in this direction.

Between alf Sct and NGC6664 and eta Aql lies the positional center of the
giant Aquila Rift, a giant molecular cloud about 0.22 kpc distant. The Rift
itself spans an apparent 25.5 x 10 degrees - a function of its nearby
location and size. At that close distance, it is estimated to be about 97
parsecs or 316 light-years on its semi-major axis. Compare that to the 1.2
parsec 3.9 light-year distant alf Cen. That's one big cloud.

A window in the molecular clouds in the Aquila direction, the Great Scutum
Star Cloud (J184321.60-065403.6) contains the mag 5.8 "Wild Duck" open
cluster M11 (NGC6705, dia. 12', J185100.00-061557.6) and showcase Barnard
Dark Clouds B111 (J185000.00-045700.0) and B119a (J185438.40-051012.0). The
Wild Duck cluster (M11) is about 1.8 kpc distant and like the NGC6664 that
you previously looked at it is part of the Sagittarius-Carina Arm. But M11
lies another 0.7 kpc beyond NGC6664 and is about 6.5 parsecs in physical
diameter. M11 is about 150 million years old or about 70% of a galactic
year (220M years). That's about entering middle age for an open cluster.
See -
http://members.csolutions.net/fisher...ClAgeChart.JPG

I do not have a distance for B111 or B119a.

Also of interest in this area dark clouds B103, B112 and B318. To find
Barnard Dark Clouds, try the Georgia Institute of Technology Online Edition
of E.E. Barnard's "A Photographic Atlas of Selected Regions of the Milky
Way" (1927) at:
http://www.library.gatech.edu/about_...ard/index.html


Download charts, tables, text and plates for Plates 36 and 37. (The charts,
text, tables and plates are available as single click, combined pdf file.)
I also have a website with supplemental J2000 charts that show how to orient
the Barnard plates to the night sky.
http://members.csolutions.net/fisher...ojectpage.html
Aqu Region Chart:
http://members.csolutions.net/fisher...dcc_aql7_1.gif

There are many Barnard clouds in this region. The best way to visualize them
is to use Barnard's original charts.

5.7 kpc in the direction of the Scutum Star cloud is the end of the 4.5 kpc
Milky Way galactic bar, although this is not optically visible to amateurs.
For a top-down view, look for photos of Milky Way analogue galaxy M95.
http://www.seds.org/messier/more/m095_more.html

Read Lopez's 2001 study on the Milky Way galactic bar:
Lopez-Corredoira, M. et al. Jul. 2001. Searching for the in-plane Galactic
bar and ring in DENIS. 2001A&A...373..139L
http://adsabs.harvard.edu/cgi-bin/np...6A...373..139L

Returning the near sky of the Local Bubble, 26 Aql is, a bright unequal
binary (4.5 G8III, 11.9) with a wide separation (116" Epoch 2000). 26 Aql
is a 3.5 deg R.A. sweep from lambda Aql. 26 Aql (HD181391) is part of the
6th orbit catalogue and a short period of 266.5 days. It is 47.2 parsecs
distant. An orbit plot is available at the 6th Orbit catalogue website:
http://ad.usno.navy.mil/wds/orb6/PNG/wds19205-0525u.png

Two bright unequal colorful doubles round out this 41 North transit window:
15 Aql - listed in Mullaney's Celestial Harvest - and 23 Aql - an entry in
the Belmont Society colorful doubles observing list. 15 Aql has a KIII mag
5.5 primary and a 7.2 secondary separated by 38.4" (Epoch 2000). Mullaney
describes it as white and lilac. It is located about 1 deg northwest of
lambda Aql.
23 Aql has a K2Iab primary at mag 5.3 and a secondary at mag 9.3, but
separated at only 3.1". So 15 Aql can probably be reached by smaller
apertures while 23 Aql will require a larger aperture scope. 23 Aql is
located about 2/3 the distance between del Aql and lambda Aql.

Bright stars 57 Aql (B), del Sct (F), 26 Aql (G) and 15 Aql (K), discussed
above, provide an opportunity for a low dispersion spectrometer spectral
class tour.

For those of you who want to try your hand at short-period variables, eta
Aql (AAVSO1947+00) is a bright (mag. 3.5) delta Cephid variable with a
period of 7.1 days. The AAVSO lists the magnitude range as 3.5 to 4.3. The
next maxima is 2006-8-14 at about 4:00 UTC; the next minima at 2006-8-19 at
about 1:00 UTC. A light curve generator is available at the AAVSO.
Plot about 40 days of data to get a feel for the light curve. Making a
series of astrophotos also is a good approach considering the max-min range
is 0.8 mags.

http://www.aavso.org/

- Canopus56

"canopus56" wrote in message
...
snip all

That's based on a W111.8 op . . .

An observing list can be printed from:
http://members.csolutions.net/fisher...00AqlPlan.html

- Canopus56