Shot photos from the driveway again last night. Several hours shooing at the heart of the Virgo cluster and Markarian’s Chain.
I was shooting color data, but clouds rolled through the field before I got any blue data. Will have to shoot again another evening. In the meantime I put together a monochrome version.
The two big elliptical galaxies towards the lower right are M84 and M86. In the center is an interacting spiral galaxy NGC4438, notably distorted through interaction with NGC4435 seen right above it. The big elliptical at lower left is M87.
Do not try to count the number of galaxies here, zoom in and dozens upon dozens become visible.
The heart of the Virgo Cluster around Markarian’s Chain.
A clear night finally appeared, clouds have been plaguing this particular dark of the Moon. What to do? Maybe do some astrophotography?
The nebula complex M17 in hydrogen-alpha
I have a new piece of kit, a ZWO ASI Air Pro that has been on back-order since November. With shutdowns in China and the rest of the mayhem it finally arrived this week.
The unit is a little dedicated astrophotography computer that makes a lot of the setup so much easier, while simplifying the snarl of cables on the telescope.
Controlling the camera, filter wheel, and guiding is done through a very nice app on the iPad. In less than an hour I had the basics figured out and was taking images.
A few technical issues to learn about through the night, such as how to best configure the WiFi for use with the home network, how to access and download the images to the desktop computer, etc., but no real problems. I took images through until dawn’s glow appeared in the data, running from twilight to twilight.
Social media is currently full of advice on what to do while stuck at home waiting out a pandemic. I find I need no advice… A dark sky and a telescope? No problem.
The observing notebook fills with notes beside the telescope
Awake at 4am this morning I pulled the Astrola from the garage and observed until the dawn lit the sky.
Once the evening clouds dissipated I again pulled out the telescope and observed for another two hours this evening.
Following the advice of staying at home I have been observing alone from our driveway. This weekend would have been our normal club dark-of-the-moon star party at Kaʻohe, getting together with other observers. Obviously this was cancelled.
This period of social isolation is measured in pages of notes on stars and nebulae, measured in the light-years I cross while peering into the universe.
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 Kea
The 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 celebrations 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…
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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 2020 is divisible by four and not divisible by 100, there will be a leap day added to the end of this February… Today.
