In this age of short product lifecycles and rapid obsolescence it is nice to see an example of longevity. We consider equipment or tools old when over ten years in service. How about a century?
A compressed gas cylinder with inspection dates spanning over a century
Our CO₂ is delivered in standard industrial pressure cylinders. These steel cylinders hold 50lbs of liquid CO₂ at a pressure sufficient to keep it liquid at room temperature, about or about 800PSI.
These standard cylinders require inspection every five years, and the inspection date is stamped into the steel at the top of the cylinder in the format month-year with a two digit year. It has been this way for a long time, longer than I realized.
The region south of Waikoloa along the shore seems to be a barren field of lava with little to offer beyond miles of dark rock and baking sun. That may seem to be the case, but there are surprising gems out in those lava fields.
Looking along the King’s Trail south of Waikoloa
The plan? As usual hike the King’s Trail south from Waikoloa, but this time explore some of the smaller trails I had passed by in the past. Perusing the satellite imagery reveals a surprising number of trails through the lava. Considering the substantial effort it takes to cut a trail through the worst aʻa lava those trails must be significant somehow.
Today is February 29th, that odd date that only occurs every four years.
The reason for a leap day inserted into the calendar, the existence of February 29th, is ultimately astronomical. Perhaps a little explanation is in order…
We originally defined days as the time it takes the Earth to rotate. While we define years as the time it takes the Earth to orbit once around the Sun. The problem is that these values do not divide evenly into one another.
Sunrise seen from the summit of Mauna KeaThe Earth takes about 365.24219 days to obit the Sun, when measured by the Sun’s position in the sky, what is called a tropical year. There are different ways to measure a year, but if one is concerned with keeping the seasons in sync with your calendar, then you are interested in tropical years.
It is that bunch of decimals, the 0.24219 etc., that is the problem, every four years the count drifts out of sync by roughly one day. The insertion of an extra day every four years helps bring the calendar back into synchronization with the orbit of the Earth and with the seasons.
Even leap years do not quite fix the problem as 0.24219 is close, but not quite 0.25 or one quarter of a day. Thus additional corrections are needed… Enter leap centuries.
Our current calendar was instituted by Pope Gregory XIII in 1582, setting up a standard set of corrections for the fractional difference between the length of a year and the length of a day. Scholars knew that errors had been accumulating in the calendar for centuries, resulting in a drift of several days. Religious authorities were concerned that this drift had displaced important celebration in the church calendar, in particular the celebration of Easter. After much argument it was decided to reform the calendar. The current solution was devised by a number of astronomers, including Aloysius Lilius, the primary author of the new system.
The Gregorian Calendar uses an extra day in February every four years, unless the year is divisible by 100, then there is no leap leap day that year. However, if the year is divisible by 400, then it is a leap year. While this may sound odd, it does create a correction much closer to the ideal value of 365.24219 days per year.
I am a geek, so let us put that into code…
1
2
3
4
5
6
7
8
9
10
if(year modulo4=0)then
if(year modulo100=0)then
if(year modulo400=0)then
leap=True
else
leap=False
else
leap=True
else
leap=False
Even this is not perfectly precise. The correction is close but will drift given enough time. The length of a tropical year also changes slowly over time. We will eventually have to add another correction to keep the calendar and the seasons in sync. But not for a few millennia, good enough, for now.
As 2024 is divisible by four and not divisible by 100, there will be a leap day added to the end of this February… Today.
Gazing up at the sky while reading the old texts one would not be amiss in believing that the stars never change. Indeed there are many who insist vehemently that the stars are eternal and unchanging. But the stars do indeed change, often quite visibly, sometimes within the span of a human lifetime.
A VLT/SPHERE image of L2 Puppis showing the enveloping cloud of gas and dust representing an early stage planetary nebula. Image credit ESO/P. Kervella used under Creative Commons 4.0
One such star is L2 Puppis.
A bright star, one of the few naked eye variable stars that could be seen to fade and reappear without the aid of a telescope much like the far more famous stars Mira and Algol. On star charts the star is found prominently drawn at magnitude 4, buf if you attempt to locate it today you will not find it without the use of a telescope.
I first encountered this star quite recently while starhopping through southern Puppis with an 8″ telescope from the driveway. The chart showed two bright stars close together, L1 Pup and L2 Pup, while the view in the finder ‘scope showed only one bright star.
