Browsing the Catalog
Messier objects; tracking the International Space Station.
Flyers fans probably know the name "Messier" as that of the long-time captain of the hated New York Rangers. For backyard astronomers, though, the name means someone else altogether. And with apologies to Mark Messier and his six Stanley Cup rings, I think the astronomers' Messier will be longer remembered.
Hey, that's not a comet
Charles Messier (1730-1817) was an astronomer. Like many astronomers, though, he wanted to be a famous astronomer, and one of the most surefire ways to do that in the 18th century was to get a comet named for you as its discoverer.
It had already worked for Sir Edmond Halley, who managed to get his name applied to what's still the most famous periodic comet (comets that are known to orbit the Sun at a regular interval) in the Solar System. More than 250 years after his death, Halley's Comet now ensures that Sir Edmond Halley gets at least a little media coverage every 76 years.
Messier found, however, that many of the "comets" he thought he'd found were actually permanent objects in the sky. These nebulae, from the Latin word for "clouds," were usually hazy smudges that could easily be confused with the coma, or center, of an approaching comet.
Messier decided that the best way to handle these was to catalog them and their locations in the sky. He published the first edition of his catalog, with 45 objects, in 1771. By the time of his death, the list had grown to 103. Astronomers have since identified another seven objects first noted by Messier or his assistant, bringing the total number of what are now called Messier objects to 110.
We've since learned that some of these "nebulae" were actually other, incredibly distant galaxies that lay far beyond the Milky Way. The Andromeda Galaxy (Messier object 31, or M31) was known as the Andromeda Nebula until Edwin Hubble (yes, it's his name on the Hubble Space Telescope) discovered galaxies in 1924. Other nebulae were densely packed clusters of stars, while others still actually were clouds―remember the Latin meaning of nebulae―of dust and gas where new stars were born.
Messier eventually did get his name on 11 comets, but it's the objects he cataloged while looking for them that ensured his fame.
Following in Messier's footsteps
The great thing about the Messier objects is that even in the light-polluted suburbs of Philadelphia, we can see quite a few of them.
The easiest of these is almost certainly M45, the Pleiades (pictured). Visible all winter with the naked eye, even during a full moon, the "Seven Sisters" (as the ancient Greeks called them) are what's known as an open cluster of very young stars. So young, in fact, that the nebular gas in which they ignited still clings to them like baby fat; you can see it in a small telescope.
They even have a cameo in the Old Testament:
Then the Lord spoke to Job out of the storm. He said: [...] Can you bind the chains of the Pleiades? Can you loosen Orion's belt? (Job 38:31)
At this time of year, the Pleiades are already headed towards the western horizon by 9:00pm, but there's still time to check them out before they disappear for the summer.
M31, the Andromeda Galaxy, already mentioned, is the second most visible Messier object. Of similar size and shape to our own Milky Way, astronomers believe that Andromeda will collide with our galaxy in the far, far distant future (no need to prepare a household emergency kit for this).
The first known description of the Andromeda Galaxy was by a Persian astronomer in the 10th century who called it a "small cloud." Indeed, that's what you'll see with the naked eye or a pair of binoculars. A telescope will allow you to distinguish the brighter light of the galactic core. If you're lucky enough to spend an hour adjusting your eyes under a truly dark sky, your telescope may permit you to make out Andromeda's majestic spiral arms.
Andromeda is about 2,000,000 light years away. That means that when you're looking at it, the photons of light striking your retina began their journey when mankind was still mostly covered in fur.
This column is far too short to go through all the easily visible Messier objects, but a handy list is available at Wikipedia. As particular Messier objects move into the spotlight in our night sky, I'll highlight them in future columns.
In the sky now
What's the size of a football field and travels at five miles per second?
If you answered "the International Space Station," give yourself a gold star. It's visible several times each week, and if you've never watched it zipping across the sky, more than 200 miles overhead, you're missing out.
A little after midnight on Monday―between 12:17 and 12:19am, to be more precise―the International Space Station will pass right through the constellation Ursa Major, better known to most people as the "Big Dipper." You'll find the Big Dipper to the north side of the zenith, the point in the sky directly overhead. The International Space Station will pass between two of the stars in the Big Dipper's "handle," Alioth and Mizar. It will be about the same brightness as the stars in the constellation.
If you miss it then, you've got a few other good opportunities this week. The station will be dimly visible, passing to the right of the waxing gibbous Moon, on Tuesday night, April 12, between 11:31 and 11:33pm. Early risers can catch it gleaming brightly between 4:45 and 4:47am on Thursday morning, April 14, as it passes just below Polaris, the "North Star." On Friday morning between 5:10 and 5:12am, it will be the brightest object in the heavens as it crosses from west to east, high in the southern sky.
Now is a pretty good time to spot the ISS because a large resupply vehicle called the Johannes Kepler is docked with it, making it appear larger and, when sunlight hits it right, brighter than normal. Its profile will grow even larger for a few days next month, when the Space Shuttle Endeavour docks with it following its final launch on April 29.
Anyone who wants to keep tabs on the ISS with their naked eyes can visit NASA's Satellite Sighting Information page for Pennsylvania.