[LVAS] Observer's Challenge Spring Supplemental - M-51 Revised Copy

[Fred Rayworth]

All,

 

Somehow, a part of Rob Lambert's description got left out of the original posting of the challenge. I have corrected that and am posting the revised challenge below. The correct version is already available on the LVAS web site.

 

Fred

 

 

 

 

MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society
Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada
With special assistance from:
Rob Lambert, Las Vegas, Nevada
Spring 2010
M-51 The Whirlpool Galaxy
Introduction
The purpose of the observer’s challenge is to encourage the pursuit of visual observing.  It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, we will be happy to include them in our monthly summary.  Observing is not only a pleasure, but an art.  With the main focus of amateur astronomy on astrophotography, many times people tend to forget how it was in the days before cameras, clock drives, and GOTO.  Astronomy depended on what was seen through the eyepiece.  Not only did it satisfy an innate curiosity, but it allowed the first astronomers to discover the beauty and the wonderment of the night sky.
Before photography, all observations depended on what the astronomer saw in the eyepiece, and how they recorded their observations.  This was done through notes and drawings and that is the tradition we are stressing in the observers challenge.  By combining our visual observations with our drawings, and sometimes, astrophotography (from those with the equipment and talent to do so), we get a unique understanding of what it is like to look through an eyepiece, and to see what is really there.  The hope is that you will read through these notes and become inspired to take more time at the eyepiece studying each object, and looking for those subtle details that you might never have noticed before.  Each new discovery increases one’s appreciation of the skies above us.  It is our firm belief that careful observing can improve your visual acuity to a much higher level that just might allow you to add inches to your telescope.  Please consider this at your next observing session, as you can learn to make details jump out.  It is also a thrill to point out details a new observer wouldn’t even know to look for in that very faint galaxy, star cluster, nebula, or planet.
 

M-51
Known also as the Whirlpool Galaxy or NGC-5194/5, it is a spectacular object to observe.  With a mag. 8.4 brightness, it is easy to spot in most any telescope and even binoculars.  However, the larger the aperture, the more details can be seen within it.
It was discovered by Charles Messier in 1774, but the spiral shape was not recognized until Lord Rosse trained his leviathan 72” reflector on it from his observatory at Birr Castle in Ireland.  It was still thought to be a spiral nebula until modern astrophotography revealed its true nature.
Though its companion, NGC-5195, is a separate galaxy, it has long interacted with the main galaxy to affect how the spiral arms formed.  This smaller companion has collided with the main galaxy several times and is currently behind it as referenced from Earth.  Visually, in smaller apertures, two bright spots can be seen with one a bit larger and brighter than the other.  However, they are both connected within the glow.
M-51 is part of the small M-51 galaxy group that includes M-63 (the Sunflower galaxy), NGC-5023 and NGC-5229.  The Whirlpool Galaxy lies about twenty-three million light-years from Earth.
James Mullaney, Celestial Harvest: 300-Plus Showpieces of the Heavens for Telescope Viewing and Contemplation
Whirlpool/Question-Mark Galaxy:  Visible in 3” as "two very unequal nebulae nearly in contact.  M-51 is typically disappointing in less than a 6”.  The spiral arms can be seen in an 8” with averted vision on a dark night.  Yet, it took Lord Rosse's 72” speculum metal-mirror to first recognize them.  This fact provides a perfect illustration of Sir William Herschel's famous dictum that "When an object is once discovered by a superior power an inferior one will suffice to show it afterwards!"  The Whirlpool can be glimpsed in binoculars on a dark night.
Burham’s Celestial Handbook, Vol 1, by Robert Burnham, Jr.
M-51 is a Sc type spiral.  A good pair of binoculars will show it on a dark night and a 2" lens will show a core with a halo.  More details pop out at larger apertures.  In 12", the spiral coils begin to resemble the familiar photographs.
The Night Sky Observer’s Guide, Vol 2, Spring & Summer, George Robert Kepple and Glen W. Sanner
In 8" to 10" scopes, has a well concentrated, mottled halo that suddenly brightens through the core to a stellar nucleus.  The bridge to NGC-5195 is undetectable.
In 12" to 14" scopes, it has a large diffuse halo containing a well-concentrated core.  Spiral arms are visible with averted vision.
In 16" to 18" scopes, the halo contains a clockwise spiral structure of two arms arcing almost completely around the core.  The spiral arms are mottled and laced with dark lanes.
Observing Handbook and Catalogue Of Deep-Sky Objects, by Christian Luginbuhl and Brian Skiff, Cambridge University Press
In 6cm (2.4”), spiral component is mottled and extensive, but well-defined halo with little brightening toward the center, then a suddenly brighter core and stellar nucleus.  In 15cm (6”), is difficult to tell which galaxy is brighter.  No bridge visible.  25cm (10”) shows the arms clearly, brought out by dark patches N and SW of center.  In 30cm (12”) the east arm is brighter, unwinding clockwise.  Core is optically "deep," glowing like an unresolved globular cluster.
Observations/Drawings/Photos
Roger Ivester (see Roger Ivester April 10.jpg):  Observer from North Carolina
The spring supplemental Observers Challenge object is NGC-5194 (M-51) and its smaller companion, NGC-5195, which lies only 4' to the north.  All observations were made from his moderately light-polluted backyard in Boiling Springs, North Carolina.
Both galaxies can be easily seen with a 60mm scope under a dark sky and good transparency.  The appearance is that of two faint nebulae, both with brighter cores, each having a stellar nucleus, with faint mostly-round halos.
A 4” refractor presents NGC-5194 as having a brighter well-concentrated middle and a stellar nucleus.  The eastern-most part of the halo has a brighter rim and curves from the south edge toward the north.  The western halo appears similar, but is not as bright, nor nearly as concentrated.  NGC-5195 appears mostly round with a brighter middle, and also with a stellar nucleus, which seems to be a bit more intense in brightness than the nucleus of the larger NGC-5194.
When observing NGC-5194 with a 10” reflector, the spiral arm on the western edge becomes very pronounced, and the overall texture begins to hint at spiral structure.  A mag. 13.5 star can be seen just off of the western edge of the core, and a fainter mag. 14 star sits just below.  A mag. 13.7 star can be seen on the eastern edge of the halo.  NGC-5195 is presented as smaller, but again with a brighter stellar nucleus as compared to the larger NGC-5194.
The sketch was made using a 10” reflector at a magnification of 190X.  Due to the poor conditions as of late, he picked a sketch from April 1994 and duplicated it as close as possible.  This sketch was made on a 5 X 8 note card, using a combination of different graphite drawing pencils.  The colors have been inverted using a scanner, and there are also some changes in contrast and brightness (see Rogers M-51.jpg).
Fred Rayworth (see Fred at Sawmill.jpg):  Observer from Nevada
Fred had two opportunities to look at this great galaxy pair for the spring supplemental.  Once in May and the other in June.  Below is a summary of the two observations.
He saw it both times from Redstone Picnic Area on the north shore road of Lake Mead, Nevada.  On May 15, 2010, what started as a bad night (clouds moving in before sunset) opened up after dark and became the best observing night of 2010, so far.  The sky was pristine, at least wherever he looked.  There was no wind and he remained in a T-shirt the whole night.
At first glace, he was wowed by the stunning detail he saw in the galaxy pair.  At 70X, it was small, a pair of bright cores with the larger one having just the hint of spiral arms.  At 101X, more details came out as the spiral arms started to show mottling and more structure.  At 220X, it was the best.  As the spiral arms spread out from the bright and large non-stellar core, he spotted individual lumps of nebulosity and what may have been some globular clusters embedded within.  A faint bridge connected to NGC-5195.  As for NGC-5195, the core seemed almost as bright as that of M-51, but the surrounding glow was much smaller and just a tad oval.  It had no other shape and he thought it to be distinctly of the elliptical variety.  It was quite a contrast to the extended spiral arms of M-51.  Overall, he got the impression that M-51 was spinning so fast, it threw a large chunk off to the side and it was still connected.  This is not likely the case, but it set his imagination wild (see Freds M-51 220X.jpg)
Upon a return visit on 05 June, 2010, the skies weren’t quite as nice, there was an erratic breeze blowing, and he was tired the moment he got there.  Still, he had a great time and had a chance to try a new 4.7mm eyepiece (390X) on it.
At 70X, 101X, and 220X, he observed the same details as the last time though they were not quite as distinct.  When he tried 390X, the image filled the field.  Both cores looked equally bright, though M-51 was a bit larger.  The spiral arms washed out so that only the brightest clumps were visible, vaguely giving it a spiral appearance.  The bridge between M-51 and NGC-5195 was gone.  Though the new eyepiece gave a nice 82° field of view, the magnification was just too high for the conditions and didn’t add much.  Overall, they looked like a pair of bright cores with “something” around one of them (see Freds M-51 390X.jpg)
Rob Lambert:  Observer from Nevada
In doing research for the Spring Supplemental Challenge, he was really surprised by the number of differing estimates regarding M-51’s distance, its size, and its brightness.  Differences varied from 15 million light years to the more accepted 37 million light years.  Estimates of its size varied from 50,000 light years to over 100,000 light years.  Estimates of its luminosity ranged from 10 billion suns to over 160 billion suns.  It’s amazing that estimates can vary this greatly.