Category: Asteroids

I made two attempts to catch dwarf planet (136472) Makemake in March. The first, in early March, was not so good, mostly the result of operator error and high thin clouds rolling across the field of view during the imaging run. During early spring here in central Oklahoma a night without clouds, high wind, and Moon is hard to come by so I wasn’t able to try again until March 27th with just two out of the three (no wind or clouds). I got better results this time out. The animations below capture just under three hours of Makemake’s movement. Image details are in the endnotes.

On this night Makemake was in the constellation Coma Berenices moving at a snail’s pace of 0.042 arcseconds/minute.  At this rate, over the course of the entire 2.75 hour imaging session, Makemake showed just under 7 arcseconds of movement.

The seeing and transparency during the session were pretty good. But, as usual, my backyard was awash in stray light from neighbors’ homes, nearby unshielded street lights, and a setting crescent Moon. And, as usual, I was looking out of my light-polluted Edmond location directly into the Oklahoma City light dome to the south. Under these conditions, I was half expecting not to be able to detect this faint object at all. But, after slewing the telescope to Makemake’s coordinates, and verifying that I was centered on the correct field, I was relieved to see Makemake’s dim pinpoint appear when the first image started building on the computer screen.

Imaging Considerations

Makemake’s slow sky motion was an important planning factor for this session. Makemake’s extreme distance from the Sun is the reason for its slow sky movement. Makemake orbits the Sun in the outer region of the Solar System known as the Kuiper Belt, a region inhabited by small icy bodies. Makemake’s average distance from the Sun is 4,253,000,000 miles (6,847,000,000 kilometers). This is nearly half a billion miles beyond Pluto. At this distance, it takes Makemake 305 Earth years to complete one orbit around the Sun. No wonder, as seen from Earth, Makemake is such a slow mover.

Because of its slow movement against the background stars, I had to plan to image Makemake for just under three hours to capture noticeable movement. Fortunately, at the time of this imaging session, Makemake’s sky motion was not at its slowest and I could plan on capturing its movement in a single-night session.

Many astro-imagers capture images of Makemeke on successive nights to show its movement against the background of stationary stars. This method avoids the tedious process of capturing hours-long image sequences on a single night, but produces a blinking depiction of Makemake’s movement rather than a smooth continuous movement.  I prefer smooth continuous movement so I opted for the single-session approach, even though it shows less total movement.

This table  shows how much Makemake’s sky motion varies and how Makemake’s sky motion compares to asteroid (2612) Kathryn, a Main Belt asteroid orbiting the Sun billions of miles/kilometers closer in than Makemake. As this table shows, even at its fastest, Makemake only squeaks out a miniscule 3 areseconds per hour.

Another consideration in imaging Makemake is the fact that it is very faint for the relatively small 8-inch/203 mm telescope that I use. Because of its distance and relatively small size (diameter 900 miles/1500 km), Makemake is very faint as seen from Earth. For the date of this session, the Minor Planet Center predicted Makemake’s V magnitude as 17.10. I measured its magnitude on the first, middle, and last images of this animation sequence and obtained an average magnitude of 17.25, a bit fainter than predicted. At magnitude 17.25, Makemake is almost 5,000 times fainter than the faintest star a dark-adapted human eye can see from an very dark location.

Polar Alignment Test

On a more technical note, this session was a trial run of using the freeware program NINA (Nighttime Imaging ‘N’ Astronomy) tool for polar aligning my Celestron CGEM mount during initial setup. Previously, I had been using Celestron’s All-Star Polar Alignment procedure (ASPA), a feature that allows a user to choose any bright star to polar align the telescope mount, not just one near the North Celestial Pole (NCP).

Like Celestron’s ASPA, NINA’s polar alignment routine does not require use of a star near the NCP. But, unlike ASPA, NINA does not require pointing at a specific star. For NINA, all that is necessary is to point the telescope at any star field anywhere in the sky with enough open sky for NINA to rotate the mount approximately 30 degrees on its right ascension/polar axis. The ability to polar align without being able to see the northern sky is important to me because the view of Polaris and the north circumpolar region is mostly blocked from my backyard by tall trees. The ability to polar align using any random patch of sky, not a specific star, was icing on the cake.

I won’t get into the details of NINA’s polar alignment process, but will say, that it was easier to use than Celestron’s ASPA because it did not require aligning the mount to the sky first, then slewing to and polar aligning on a specific star, and then performing another star alignment with a properly polar-aligned mount. NINA’s procedure allowed me to polar align first on a random patch of sky and then align the mount to the sky using Celestron’s automated StarSense alignment system. This arrangement, with the mount polar aligned first, saved much time in the star alignment process. Details on using NINA’s polar alignment tool can be found here.

In general, the results of NINA’s polar alignment function were pleasantly surprising. I found the tool quite easy to use, and fast. Probably the easiest and fastest method I’ve ever used for polar alignment.  Far superior to the painful and time consuming drift alignment method, and easier and faster than SharpCap Pro and Polemaster.

The accuracy of NINA’s polar alignment also seemed quite good, although determining the accuracy is a bit of a trick. I stopped the alignment process when the NINA display showed I was aligned to within 37 arcseconds of the NCP. On this Celestron CGEM mount, stickiness of the azimuth and altitude knobs makes further refinements in polar alignment a time-consuming and often fruitless exercise. This remaining amount of polar alignment error is plenty good enough, and can be easily compensated for by the guiding software, PHD2 and my 50 mm SVBONY guidescope. Indeed, on this evening, my guiding error, as measured by PHD2, bounced around between 0.70-0.80 arcseconds, a very comfortable margin, well inside the 1.02 arcsecond/pixel scale of my telescope-camera system.

From these results, measured by three independent methods, it’s hard to say just how precisely my mount was polar aligned. At best, it was within 37 arcseconds of the north celestial pole. At worst, it was within 2.4 arcminutes (144 arcseconds). But, even at its worst, this single instance is an improvement over what I was getting using the Celestron ASPA process. Polar aligning with Celestron’s ASPA procedure and measuring the error with Celestron’s CPWI and PHD2 showed that I was typically getting between 2.5-5.0 arcminute polar alignment error. Only more experience and data points will tell if NINA consistently provides better polar alignment. I will continue to gather more data.

Conclusion

Overall, this was a productive imaging session. I am now confident that my rig can detect 17th magnitude point source objects from my light-polluted Bortle 7 backyard.  I’m looking forward to pushing the limits further by imaging dwarf planet Haumea, a slightly fainter Kuiper Belt neighbor of Makemake.  I am also pleased with NINA’s polar alignment tool. So much so, that even if its precision is no better than Celestron’s All-Star Polar Alignment process, I will continue using it for its ease of use and considerable time savings in setting up for an imaging session.

Image Details:

1. Date/Time: March 27, 2023 04:29:02-07:12:33 UT
Location: Edmond, Oklahoma USA
Seeing: Fair-Good; Transparency: Poor;  Sky Brightness: Bortle 7
2.75-hour time lapse animation.
9 images, each a stack of 20 @ 60 seconds (total 1200 sec per image). Gain 250.
Orientation: North up. East left.  Up is 1.4 degrees E of N
FOV: 28.6 x 15.6 arcmin
FOV Center: 13h 17m 43.931s  +22° 25′ 18.387″
Telescope: Celestron C8 (203mm SCT f/10) operating at f/5.8 (Celestron f/6.3 Focal Reducer/Flattener + 128.5 mm spacers)
Camera: ZWO ASI482MC
Capture: SharpCap Pro
Guiding: PhD2
Processing: Deep Sky Stacker, GIMP
Photometry: Astrometrica

2. Same as above except:
FOV: 15.3 x 9.99 arcmin (cropped/resized animation)
FOV Center:   13h 17m 47.309s  +22° 24′ 05.224″