Well it has been quite cloudy this week, but the clouds opened up just enough to try to get some more images of the sun, which now has at least one visible sunspot. In addition, we continue following the research into the gravitational wave event S190510g, thought to be the merger of two neutron stars.
So, this time, when the clouds gave way to bright sun and shadows, we wanted to try the Nikon Coolpix P1000 camera and see how it worked with solar observing. In the image below you can see the camera setup on the Sky-Watcher lightweight mount.
|Resident Astronomer points camera and takes images of the sun (Source: Palmia Observatory)|
The mount was slewed to the sun and just a minor position correction was required. After all, the initial alignment was just eyeball pointing level and northward. The image below was at pretty much full focal length (3000mm by camera setting, but really about 1800mm effective focal length compared to 35mm APS-C film standards). So, now, we only see one visible sunspot; the other one having apparently rotated out of view.
In the previous post of May 12, 2019, we showed images of two visible sunspots taken with a DSLR, but with 600mm telephoto lens, which clearly showed each sunspot really being a pair of sunspots. The sunspots come in pairs because of high magnetic fields on the sun as illustrated in the following screenshot from "windows2universe.org."
|Solar sunspots come in pairs due to solar magnetic fields (Source: windows2universe.org)|
The sunspot image above can be expanded and you can sort of identify that the sunspot is really a pair of darker areas on the sun. The detail in this photograph is not as great as expected, especially when compared to the expanded view shown in the May 12 post, with just a 600mm lens. If you go back to that previous post you can see that the improvement by going to longer focal length (1800mm vs. 600mm) did not seem to be that great.
|Measured separation between sunspot pair (19.7 pixels apart) taken with (app) 1800mm lens (Source: Palmia Observatory)|
So, given the camera sensor sizes and other parameters we see the distance between sunspots is around 15 arcseconds for the 600mm lens and about 26 arcseconds for the (app) 1800mm lens. But there are some differences between the two measurements including being made on different days and using different apertures and exposure settings. So this is just a first measurement and a first approximation. The difference is not due to diffraction limiting which is about 1.5 arcseconds for lenses in the 95mm (600mm lens) and 77mm (1800mm lens) aperture range.
Now, I had hoped to investigate these features and go under the hood to get a little better view of the images in the field and perhaps try out better focusing and see whether or not the autofocus feature would work for bright images like the sun. But it was not to happen today because the camera battery was exhausted and I didn't have a charged spare.
|Resident Astronomer goes under the hood with camera and takes images of the sun (Source: Palmia Observatory)|
By the way, in the previous post of May 12, 2019, is was reported that the Sky-Watcher mount didn't seem to have a solar pointing and tracking mode, so the adopted backup plan was just to slew to Mercury, which is quite near the sun in the sky and then just toggle the mount to point directly at the sun. Well, it turns out, after further investigation, that the mount does have a solar pointing mode. It is just hidden under several layers of icons and clicks to say that you understand the dangers of pointing a telescope at the sun. Ok, ok, we understand the dangers, but the iPhone app had one more trick that it sprang on us and that is the screenshot shown below. Yes, that is correct, you had to demonstrate that you were awake enough or sober enough or whatever to be able to correctly add two numbers together before the mount could be slewed to the sun.
|iPhone Sky-Watcher control app has math quiz to enter sun pointing mode (Source: Palmia Observatory)|
Finally, we can report further on the ongoing gravitational wave event S190510g, which as you recall from the May 12 post was expected to be the merger of two neutron stars. Well, ever since that first chirp alert showed up on the iPhone app on May 10, there have been now over 55 subsequent chirp alerts describing the findings of many other observatories that tried to find the electromagnetic counterpart to the merger event.
But how to find the electromagnetic counterpart, here understood to be either visible light or x-rays or radio waves and also including neutrinos and ensure that the counterpart found was actually associated with the gravitational wave event. Recall, as originally posted on May 12 and shown below, the possible area where the event actually occurred covers a wide range. With only three LIGO type observatories, the possible sky location of the event covers over 5500 square degrees.
Many of the 55 follow up alerts reported no visible optical transient in the area of sky that a given observatory could search. However, two observatories did find optical transients, occurring about the same time as the gravitational wave event. The screenshot below, courtesy of Moscow State University Observatory, shows a transient of magnitude 17.6. Is this transient associated with the GW event or is it just a coincidentally occurring supernova or other astrophysical event?
|Optical transient observed in the GW skymap location (Source: Moscow State University)|
Another chirp alert from the Gaia Collaboration reported a separate optical transient as separate location as shown in the screenshot below.
|Chirp alert from Gravitational Wave iPhone app showing observed optical transient (Source: GAIA Collaboration)|
Wow, so identifying possible sky locations for the GW merger event is just the first part of the problem. Then the sky must be searched to find an optical counterpart and then make sure that the selected optical counterpart is the real deal and not just some supernova or other transient event that occurred at about the same time as the supposed GW event. Hmm, watching all of the incoming chirp notices on the iPhone app is going to continue to be interesting to see how all of that is done. In the meantime, this Resident Astronomer is going over the textbook, "Interferometric Gravitational Wave Detectors" with some other dedicated students who have been studying their book for as long I've seen them on their study bench!