6/16/2020. This is my photograph of Messier 51, The Whirlpool Galaxy and the smaller galaxy NGC 5195. This is an interacting grand-design spiral galaxy. M51 lies in the constellation Canes Venatici. It can be seen faintly in a dark sky with a good pair of binoculars. It can be found just off the bottom of the handle of the Big Dipper, Ursa Major, almost perpendicular to the end of the spoon handle.

The Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated as number 51 in Messier's Catalog. The Whirlpool was the first galaxy to be classified as a spiral galaxy. Its distance is estimated to be 23 million light-years away from Earth. This galaxy is almost on top of us when compared my last post of a photograph of a tiny NGC 4567 which is 60 million light years away.

The graceful winding arms of spiral galaxy M51 appear like a grand spiral staircase sweeping through space. They are actually long lanes of stars and gas laced with dust. Beautiful arms are a hallmark of grand-design spiral galaxies. The spiral arms are star-formation factories, compressing hydrogen gas and creating clusters of new stars.

Some astronomers think that the Whirlpool’s arms are particularly prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of the bottom arm in my photo. The small compact galaxy appears to be tugging on the arm creating tidal forces which trigger new star formation in M51 and are lighting up the spiral arms. The Hubble telescope shows that NGC 5195 is passing behind M51 and not just dangling off the end of the spiral arm. The smaller galaxy has been gliding past the Whirlpool for hundreds of millions of years.

The Whirlpool Galaxy is interacting with this smaller companion, NGC 5195 also designated as Messier 51b. This dwarf galaxy is connected to the Whirlpool by a tidal bridge of dust. The bridge is visible in my photograph silhouetted against the central region of the smaller galaxy. Surprisingly enough astronomers thought that M51 was a cloud of gas and not a small island universe of stars until Edwin Hubble using the Mt. Polomar telescope in the 1920's proved that the galaxy was far, far away and comprised of billions, and billions of stars.

Understanding what a galaxy was made of was a big, big question for astronomers going all the way back to 1773. To get a better view of it the 60" telescope was built on Mt. Wilson. That telescope didn't answer the question. Then came the 100" telescope at Mt. Wilson. Dammit, still couldn't tell! Finally, the 200" telescope at Mt. Polomar was built. The mirror was hauled up the mountain with mules. That 16.6 foot in diameter mirror shockingly revealed that a galaxy is made of stars. Edwin Hubble observed Seyfert Variable stars in the nucleus. Seyfert stars are all about the same size and seem to burn at the same brightness and temperature. They are like a light bulb in that respect.

If you knew the brightness of a 100 watt light bulb, by measuring the luminosity of a distant 100 watt light bulb with an instrument, you could compute how far away it is away from you. Light diminishes in brightness by the square of its distance (the inverse square law). It took many years for me to finally figure out why my dates in high school and college always fell asleep on me while we were conversing in the back seat of my old '57 Ford.

In passing I wanted to mention that this photograph was only 32 exposures out of the 100 exposures that I had planned. No sooner had I started photographing M51 the sky clouded over. Hopefully I will have a better sky tomorrow and can finish this photograph. Clear skies to you. Ken Adler