Periodic Table of Messier Objects
Here’s a really cool thing made by Tom Urbain that sorts and groups all the star clusters, nebulae, galaxies and other objects in the Messier catalogue to give a very helpful overview. If you haven’t come across the Messier catalogue before, have a look at https://starlust.org/messier-catalog/ where Tom explains how it came about. Tom’s website, https://starlust.org/ is well worth a visit for all the other space goodies, including articles, films, podcasts and apps.
What is the table?
It’s a reorganised version of the Messier catalogue that makes it easy to choose a target for viewing or imaging based on your equipment, skill level, the season and the type of object. The layout is inspired by the periodic table of elements which makes it very effective in sorting the objects into a sensible pattern. There are, of course, many interesting objects that were left out of Messier’s catalogue so even if you have seen all these, there are still plenty of others to explore (particularly solar system objects and nebulae).
Click on link to view table: Messier Periodic Table
Periodic table of deep-sky objects by Tom Urbain, with permission.
The Main Groups
There are 5 main groups on the table, labelled very easy to very hard from left to right.
Each difficulty group is arranged by magnitude (an indication of brightness) from top left. Follow the white lines between tiles that zig zag down the group. A bright object will have a lower magnitude than a dim one. A word of caution though. For diffuse nebulae, the brightness is smeared out all over the object while an open cluster of the same magnitude will look much brighter because the light is all concentrated within the pinpoint boundaries of the stars.
Reading the Table:
The table is based on viewing with an 8” reflector so if you know your equipment is significantly different from this, you might want to choose the easier targets at first or feel able to jump straight into the harder ones.
Colours indicate the type of object with a key under the table. If you are interested in globular clusters, for example, look for all the green tiles and so on.
This makes it easy to scan through for objects to view right now. It’s worth having a look at the season either side if you have low horizons to East or West.
This identifies the object so you can cross reference with other websites, books and apps.
This is a good indication of brightness. Low number = bright
Taking a look at the way the colours are arranged across the diagram makes it clear that open clusters (orange) tend to be easier (left) and brighter (top), galaxies (blue) tend to be dimmer (bottom) and more difficult (right) while globular clusters (green) mostly occupy a band between the two. Nebulae (purple) and unique objects (yellow) are scattered around the table but few are very easy or very bright. I find this helps me to manage my expectations but it certainly doesn’t stop me having a crack at something difficult.
If you have an imaging setup with a sensitive camera and you stack frames, you will probably find the hard and very hard objects are all possible to image. If you prefer the simplicity of imaging with a phone at the eyepiece, you will find the easier and brighter objects more rewarding.
Searching the table
Where the table becomes really powerful is when you want to find something in particular. Maybe you want to find easy galaxies that are visible in spring. In this case you just scan all the blue tiles in the easy group to see which have spring in the top line.
I love this table and find it extremely helpful in selecting suitable targets. Thanks to Doug Edworthy for posting this on our facebook page and top marks to Tom Urbain for a stunningly good idea. It takes a lot of the work out of finding appropriate targets and keeping an eye on what might be coming up next.