Before I can start actually measuring the position of stars, I need to know which stars I’m after. In a previous post, I mentioned that I was working on that list, but I’ve now completed that list and have decided to include 500 stars.
So here it is.
The ultimate goal behind the observation of these stars is to be able to produce a star catalog similar to the Uranometria. This objective helped shape the decision on which stars to include in several ways.
First, since the Uranometria was focused on depictions of constellations and I’m intending to follow suit, only stars in constellations that were completely visible from my latitude in St. Louis. This is why the bright star Fomalhaut is not included as much of the rest of its parent constellation (Picis Austrinius) barely gets above the horizon.
This same condition could truthfully be applied to some other stars, but I felt compelled to include them as the constellations in which they lie are along the ecliptic. In other words, they’re the constellations of the zodiac and due to their historical importance it would be odd to exclude them.
Next, I had to consider the brightness of the stars. St. Louis has a great deal of light pollution. Last night I estimate that I was unable to see stars much fainter than magnitude 1.51. However, if I only included the stars I could see within city limits, it would be a very short list. Rather, I continued to add stars until I felt that the resulting star map would be well fleshed out.
However, this ended up excluding two constellations visible from my location: Sextans and Vulpecula. If you haven’t heard of them, I’m not surprised. They don’t contain any particularly bright stars and they’re both quite small. In addition, they were not recognized in period. You may notice that some of the constellations are marked (PP) which I’m using to indicate that they were only recognized post-period. This is not to imply that these stars weren’t there, but only that their constellations were defined at a certain point.
As such, in producing my star catalog, I will not be giving them a depiction in and of themselves, but rather they will likely lie along the edges of the depictions of the more important constellations.
Ultimately, the list includes stars with magnitudes as faint at 4.32. While, under ideal conditions, this is easily seen by the naked eye2, the amount of light pollution will severely limit how many of these can be regularly seen. This makes it abundantly clear how important it will be to take this instrument to more remote camping events and likely some independent observing sessions at dark sky locations.
Another key feature of this table is that it can be sorted by the right ascension. This is extremely handy since the sidereal time is defined as the hour angle of the vernal equinox. Since the hour angle is in turn defined by the angular distance between the observer’s meridian and the hour angle of the object in question (here, the vernal equinox), that ends up being the same and the right ascension. Thus, knowing the sidereal time tells you what right ascension is currently transiting the meridian.
This is super handy because it allows me to easily plan out a night’s observing. Prior to going out, I can simply check what the sidereal time will be around when I wish to start, and see, in sequence, which objects we should target.
My current plan is to take the quadrant out for its first light this coming Friday (July 20). Here’s hoping for clear skies!
- If you’re not familiar with the magnitude system, brighter stars are lower numbers and it can even go negative for a few stars. It’s also based on the human eye which isn’t linear. Astronomers have formalized the definition of magnitudes such that a star 5 magnitudes fainter is actually 100 times as faint in absolute terms.
- Under ideal dark sky conditions, it’s generally considered that about magnitude 6-7 is the best we can see with the unaided eye, depending on eyesight.