Messier Monday: The Little Dumbbell Nebula, M76

"Like many dying stars, this has created a bi-polar planetary nebula, where you get two “lobes” of gas on either side, with a donut-shaped region at the center. Viewed right down the center of one of the lobes, this would look like a ring, but since this is viewed from the side, we see mainly the lighter, rapidly expanding gas farther away with the heavier nitrogen and oxygen closer to the center."

Messier Monday: The First Extragalactic Globular, M54

"What’s amazing is that, over the long term, this galaxy will be completely captured by the Milky Way, but it will likely remain in a very long-period orbit for many billions of years, remaining intact even as its parent galaxy is cannibalized by our own."

Messier Monday: A Titan in a Teapot, M69

"Messier 69 is so old that all the O, B, A, and even F-class stars have run through their entire life cycles. Even the brightest and bluest G-stars have died; the most massive main-sequence stars left in Messier 69 are G2-stars, the same class as our humdrum Sun. That places the age of this cluster at around 13.1 billion years, meaning that the stars in here formed when the Universe was only 700 million years old!

This isn’t that strange; globular clusters are often among the oldest objects known in the Universe, and even the Messier catalogue contains some that are older than this one. But when we look at the elements present inside, that’s where Messier 69 starts to look funny."

Messier Monday: The Flattened Fake-out Globular, M19

"In reality, what we’re looking at is a huge globular cluster, some 70 light-years in radius and containing about 1,100,000 times the mass of our Sun inside of it: one of the largest globular clusters in our galaxy! At 29,000 light-years distant, it’s slightly on the other side of the galactic center from us, and its stars are typically about 11.9 billion years old, or nearly three times the age of the Sun."

Messier Monday: The Dumbbell Nebula, M27

"When you think of the stars in the night sky, they may seem eternal, but you know better. In fact, the vast majority of the brightest ones we can see are either very bright, young blue giants that are destined to be short lived, or old, red giants that have burned through the majority of their fuel. In both cases, these stars are nearing the end of their lives. But did you know that — just beyond the reach of your naked eye’s capabilities — lie a number of recently deceased red giants that were bright, shining stars just a few hundred thousand years ago?"

Trivia time for Messier Monday: which of the Messier objects (above) was the first that Charles Messier himself discovered, that hadn't been seen by anyone else previously? (Hint: it's not Messier 1!)