M51 Whirlpool Galaxy

M51 Whirlpool Galaxy; Captured from Colorado Springs, Colorado with ASI2400, Big Zeus, LeXtreme filter; 1April2023

Fun facts

The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus.  It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is about 31 million light-years (9.5 Mpc) away from Earth and 76,900 ly (23,580 pc) in diameter.

What later became known as the Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier’s catalogue as M51.  Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre Méchain, although it was not known whether it was interacting or merely another galaxy passing at a distance. In 1845, William Parsons, 3rd Earl of Rosse, employing a 72-inch (1.8 m) reflecting telescope at Birr Castle, Ireland, found that the Whirlpool possessed a spiral structure, the first “nebula” to be known to have one. These “spiral nebulae” were not recognized as galaxies until Edwin Hubble was able to observe Cepheid variables in some of these spiral nebulae, which provided evidence that they were so far away that they must be entirely separate galaxies.

The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated that the Whirlpool and its companion galaxy are indeed interacting. Sometimes the designation M51 is used to refer to the pair of galaxies, in which case the individual galaxies may be referred to as M51a (NGC 5194) and M51b (NGC 5195).

Other Catalog Designations: Question Mark Galaxy, Rosse’s Galaxy, Spiral Nebula, Whirlpool Nebula, NGC5194, PGC47404, UGC8493, Arp85,
Subtype: Spiral Galaxy
Distance from Earth: 31 million light years
Diameter: 76.900 light years
Visual Magnitude: 8.10
Constellation: Canes Venetaci

{From: https://en.wikipedia.org/wiki/Whirlpool_Galaxy & Stellarium}


Polar alignment: QHYCCD camera (controlled by Polemaster)
Imaging stream: Orion 10″ f/8 Ritchey-Chretien Astrograph Telescope, ZWO ASI2400MC imaging camera with Optolong L-eXtreme LP filter.
Mount: Sky-Watcher EQ6-R Pro Equatorial Mount (controlled by EQMOD)
Autoguider: Orion 60mm Multi-Use Guide Scope, Orion StarShoot AutoGuider Pro Mono Astrophotography Camera (controlled by PHD2)
All equipment controlled by HP Probook running Sequence Generator Pro v3.2.0.660.

Capture & processing notes

This image is “first light” with DSO CTRL 2, which I finally set up properly after over a month of missing this-or-that setting.  Once the clouds cleared at about 2300MDT, the imaging went relatively smoothly.  Except for the laptop deciding it was going to implement the Fox Security update in the middle of the session!  When I came out to do the meridian flip (~0145MDT), I discovered that the laptop was shut down.  Luckily it’s possible to return the EQ6-R to it’s home position manually (I haven’t figured out how to do that with the Southern Cross mount.  Started the night with 5minute exposures, but after the first one, decided (because of the LeX) I needed to up the exposure time to 10 minutes.  The image is the stack of the two 5-minute and 33 10-minute exposures.
Sequence plans: Gain: 158, Temp: -0°C, offset=30. BZ LeX 2x5min, 33x10min. Captured 1Apr2023, 2324MDT – 2Apr2023, 0549MDT. Total exposure time: 5:40hrs
Capture: 1 April 2023
Shooting location: Colorado Springs, Colorado
Processing: Stacked in APP, processed in LR/PS.