48-minute time-lapse animation of main belt asteroids (41) Daphne and (1369) Ostanina as imaged through an Orion ST-80 telescope with ZWO ASI482MC camera. Also shown is the active galaxy Markarian 937. The animation consists of seven images, each a stack of 12 @ 60 seconds. Field of view is approximately 60 x 40 arcminutes. North is up. East is left. Click on the image for a larger version in a separate window.

As previously mentioned, the night of November 6-7 was a three-target night. I’ve already posted about the first target, (1278) Kenya. The second and third targets came together as a pair in the same part of the sky. The pair consisted of main belt asteroids (41) Daphne and (1369) Ostanina.  Also, as noted in my earlier post, this session was part of an ongoing trial of using my Orion ST-80 telescope for imaging brighter main belt asteroids.

The seeing for this part of the session continued to be poor, but quickly deteriorated to extremely poor with high thin clouds moving in overhead. Finally, with the starfield brightening and dimming so much that the guidescope was unable to maintain its lock on guide stars, the session was scrubbed with a little less than one hour of usable imaging data. Just enough data was salvaged, however, to show some asteroid movement against the background star field.  Despite the poor imaging conditions, a small faint bonus object, Markarian 937, showed up just above the background noise in the salvaged images. More about it below.

The cropped images below show each asteroid’s actual sky movement alongside a finder chart produced by the Lowell Observatory’s online Asteroid Finder tool. Click on each image for a larger version in a separate window.

(41) Daphne


The immediate field around (41) Daphne with a finder chart showing its predicted position and movement during a three hour period encompassing the 48 minutes of this animation. The chart was produced with the Lowell Observatory’s online Asteroid Finder tool. Field of view approximately 30 x 30 arcminutes. North is up. East is left.

(1369) Ostanina

The immediate field around (1369) Ostanina with a finder chart showing its predicted position and movement during a three hour period encompassing the 48 minutes of this animation. The chart was produced with the Lowell Observatory’s online Asteroid Finder tool. The active galaxy Markarian 937 shows up very faintly at V magnitude 15.5. Field of view approximately 30 x 30 arcminutes. North is up. East is left.

Sky Movement and Magnitude

During this session, both asteroids were moving across the sky against a background of stars in the constellation Pisces. 

As predicted by the Minor Planet Center, (41) Daphne was moving at 0.27 arcseconds/minute toward 233.4°. And, (1369) Ostanina was moving at 0.19 arcseconds/minute toward 207.7°. 

The measured V magnitudes for both objects was close to the Minor Planet Center’s predicted magnitudes as shown in this table:

Asteroid V mag
(measured)
V mag
(predicted)
(41)      Daphne 12.7 13.0
(1369) Ostanina 15.3 15.2

More About (41) Daphne and (1369) Ostanina

(41) Daphne and (1369) Ostanina are main belt asteroids that orbit the Sun between the orbits of Mars and Jupiter. On this night, (41) Daphne was 2.5 AU from Earth and 3.3 AU from the Sun.  (1369) Ostanina was closer to us at 1.9 AU and 2.8 AU from the Sun.

Even though (41) Daphne was more distant than (1369) Ostanina, it appears much brighter in these images because it a much larger object. With a diameter of 205 km, (41) Daphne is nearly five times the size of (1369) Ostanina, which is only 42 km in diameter.  As a much larger object, (41) Daphne reflects more sunlight and therefore appears brighter.

Markarian 937

As mentioned above, this session was another test of using my small Orion ST-80 telescope for imaging bright main belt asteroids. As part of the testing, I have been trying to gauge the limiting magnitude for one-minute exposures using this telescope and ZWO ASI482 camera. Although some of the image processing tools I’ve been using indicate a limiting magnitude of 15.7-15.8, it is always helpful to have objects of known magnitude in the image for additional confirmation.

After finding out that Markarian 937 was in the field of view, I researched its magnitude and was surprised to find out that eleven different catalogs and surveys gave very different V magnitudes for it. The magnitudes varied from the bright end at 13.2 to 16.0 at the faintest. This is quite a discrepancy. At worst, discrepancies on the order of 0.5 – 1.0 might be expected, but nearly three full magnitudes is a bit much. Using the astrometry-photometry program ASTAP, I measured Markarian 937’s V magnitude as 15.5 on my images. V magnitude 15.5 is very close to the 15.7-15.8 limiting magnitude derived from analysis of images from previous sessions. And Markarian 937 certainly looked this faint on my images.

After digging a bit deeper, I’ve settled on a guess as to why the different reference sources report such divergent magnitudes for this object. It turns out that Markarian 937 is a Seyfert galaxy. Seyfert galaxies are one of two types of so-called active galaxies, the other being quasars. Active galaxies, or their nuclei, are known to vary in luminosity over periods of days, months, or years. So, I think it might be reasonable to infer that Markarian 937’s three-magnitude variation might be attributable to actual changes the luminosity of its nucleus over the span of years covered by the different surveys that measured its magnitude in the V band.

I don’t claim to have any great expertise in this area, but that’s my working hypothesis. Mystery solved?   

Full details for this session follow.

Observation Details
November 7, 2023 04:48:56-05:36:30 UT
Seeing: Poor-Extremely Poor    Transparency: Poor     Sky Condition: Bortle 7
Location: Edmond, Oklahoma USA

Image Details
48-minute time-lapse animation. Originally planned for 1.5-2.0 hours, but session cut short by deteriorating seeing and clouds.
5 images, each a stack of 12 @ 60 seconds (total integration per image 720 seconds/ 12 minutes).
Gain 250
FOV:

  1. Animation 1, asteroids 41 & 1369, 800×500: 61.7 x 38.5 arcmin / 1.03° x 0.64° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)
  2. Animation 2 asteroid 41, 400×400: 30.8 x 30.8 arcmin / 0.51° x 0.51° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)
  3. Animation 3 asteroid 1369, 400×400: 30.8 x 30.8 arcmin / 0.51° x 0.51° (cropped from original 1920×1080, 98.5’x55.4’ / 1.64°x 0.92°; original scale 3.08 “/pixel)

North up. East left.

Equipment
Telescope: Orion ST-80 (80 mm f/5) + Orion Field Flattener + Baader Fringe Killer Filter
Camera: ZWO ASI482MC
Guide Scope: SVBONY SV165 (30 mm f/4)
Mount: Celestron CGEM

Image Capture & Processing
Capture: SharpCap Pro
Guiding: PHD2
Process: Deep Sky Stacker, GIMP
Astrometry/Photometry: ASTAP, Tycho Tracker

NOTE:  January 23, 2024. Post edited and re-formatted.

This 72-minute time-lapse animation of main belt asteroid (1278) Kenya was captured with an Orion ST-80 telescope and ZWO ASI482MC camera.  The animation consists of 7 images, each a stack of 12 @ 60 seconds. The field of View is approximately 60 x 40 arcminutes. North is up. East is left. Click on the image for a larger version in a separate window.

The night of November 6-7, was a three-target night. First up was a single asteroid (1278) Kenya, which I will cover here. The other two targets will follow in a separate post.  For this session, I continued trial use of my Orion ST-80 telescope for imaging main belt asteroids. 

The seeing for this session was poor with very thin high clouds passing through the field of view. While capturing images, there was noticeable dimming and brightening of the star field. Nevertheless, I was able to capture enough usable imaging data to produce a little over an hour-long time-lapse animation.

The cropped animation below show (1278) Kenya’s actual sky movement alongside a finder chart produced by the Lowell Observatory’s online Asteroid Finder tool.

This cropped portion of the animation shows the immediate field around (1278) Kenya with a finder chart showing its predicted position and movement over a three hour period. The chart was produced with the Lowell Observatory’s online Asteroid Finder tool.  The field of view approximately 30 x 30 arcminutes. North is up. East is left. Click the on image for a larger version in a separate window.

Sky Movement and Magnitude

During this session, (1278) Kenya was moving across the sky against a background of stars in the constellation Cetus. 

As predicted by the Minor Planet Center, (1278) Kenya was moving at 0.67 arcseconds per minute towards 281.1°.

(1278) Kenya’s measured V magnitude was close to the Minor Planet Center’s predicted magnitude as shown in this table:

Asteroid V mag
(measured)
Vmag
(predicted)
(1278) Kenya 13.6 13.4

More About (1278) Kenya

(1278) Kenya is a stony or silicate S-type asteroid. It is 19 km (12 miles) in diameter and moves around the Sun in the main asteroid belt between the orbits of Mars and Jupiter. On this evening, (1278) Kenya was 1.08 AU from Earth and 2.04 AU from the Sun.

(1278) Kenya was discovered in 1933 by astronomer Cyril Jackson at Union Observatory in Johannesburg South Africa.

Observation Details
November 7, 2023 03:02:07-04:14:22 UT
Seeing: Poor    Transparency: Poor    Sky Condition: Bortle 7
Location: Edmond, Oklahoma USA

Image Details
72-minute time-lapse animation.
7 images, each a stack of 12 @ 60 seconds (total integration per image 720 seconds/ 12 minutes).
Gain 250
FOV:
1. 61.6 x 38.6 arcmin/1.03° x 0.64° (cropped and resized from original 1.64°x0.92°; 3.08 “/pixel)
2 30.8 x 30.8 arcmin/0.513° x 0.513° (cropped and resized from original 1.64°x0.92°; 3.08 “/pixel)
North up. East left.

Equipment
Telescope: Orion ST-80 (80 mm f/5) + Orion Field Flattener + Baader Fringe Killer Filter
Camera: ZWO ASI482MC
Guide Scope: SVBONY SV165 (30 mm f/4)
Mount: Celestron CGEM

Image Capture & Processing
Capture: SharpCap Pro
Guiding: PHD2
Process: Deep Sky Stacker, GIMP
Astrometry/Photometry: Astrometry.net, ASTAP, Tycho Tracker

NOTE:  January 27, 2024. Post edited and re-formatted.

I finally completed modifications to my Orion ST-80 (80 mm f/5) telescope and gave it a test run on the night of October 30th into the morning hours of October 31st. The modifications included replacing the original 1.25-inch focuser with a GSO 2-inch focuser, an Orion field flattener (to reduce field curvature distortion of star images), and a Baader Fringe Killer filter (to reduce violet-blue halos around the stars caused by chromatic aberration). The animation below shows asteroids (55) Pandora and (60) Echo, the targets for this first light test of the upgraded ST-80 paired with my ZWO ASI 482MC camera.

Asteroids (55) Pandora and (60) Echo in the constellation Pisces on October 31, 2023. This animation shows two hours of asteroid movement. (55) Pandora was at V magnitude 11.6 and moving at 0.17 arcseconds per minute (10.2 arseconds per hour). (60) Echo was at V magnitude 12.3 and moving at 0.20 arcseconds per minute (12.0 arcseconds per hour).  IC 1496 and IC 1492 are distant background galaxies at V magnitudes of 15.5 and 15.2 respectively. Field of view 1.56° x 0.86°.  North is Up. East is left.

I chose these targets because I wanted a field of view with two asteroids for visual interest, and I wanted to see how deep this telescope-camera combination scope could go. Conveniently, the field of view containing these two asteroids also contained two faint galaxies, IC 1492 and IC 1496.

The Minor Planet Center (MPC) predicted that (55) Pandora would be at Visual magnitude 11.6, and (60) Echo at 12.3. Both within easy reach of this scope-camera combo. The galaxies, however, were considerably fainter with IC 1492 at Vmag 15.2 and IC 1496 at Vmag 15.5. The galaxies would be the test of how deep this scope-camera combo could see. Additionally, I wanted to see how deep this scope-camera combo could go just using ten-second exposures.

The animation above shows the result. It consists of eight images taken over a two-hour period. Each image is made up of a stack of ninety 10-second sub images providing a total integration time per image of 900 seconds/15 minutes.

My hope in this project was to upgrade this inexpensive little scope to make it useable as a lightweight travel, EAA, outreach, and astrophotography telescope.

As I’ve previously posted, the Orion ST-80 is a simple achromatic refractor that trades off optical quality for very low price. One of these scopes sells now for $110 new.

Unfortunately, while very reasonably priced, as would be expected from an achromatic telescope, the scope suffers from severe chromatic aberration and field curvature. These two optical defects, common to achromats, cause noticeable violet-blue fringing around star images and distorted star images toward the outer edges of the field of view. Previous use of this scope showed that the field curvature was so bad that only about the central 30% of the field of view presented undistorted star images and the chromatic aberration produced large violet-blue halos around the stars across the entire field of view.

My plan to correct these issues was to insert an Orion Field Flattener and a Baader Fringe Killer filter in the optical path between the camera and the telescope. I had previously tested the Baader Fringe Killer and found that it did a good job eliminating the ugly violet-blue fringe halos around the stars. The field flattener, however, is new. But, because it is a two-inch accessory, I had to replace the ST-80’s original 1.25-inch focuser with a focuser having a two-inch draw tube.

Trying to complete this project on a limited budget, I chose the GSO 2-inch Crayford-style focuser from Agena Astro. With its two-inch threaded draw tube, the Orion Field Flattener screwed right on to the end of the focuser tube, and my ZWO ASI 482MC camera – with the 1.25-inch Fringe Killer filter screwed inside the camera just above the imaging chip – attached to the back of the field flattener with just the right spacing. As a bonus, this dual speed focuser provides for much finer focusing adjustments than the original focuser.

Looking at the images that produced the animation above, I am quite satisfied with the performance of this upgraded scope. The Baader Fringe Killer filter eliminated most of the violet-blue fringing around the stars, much of which disappeared anyway when I drastically lowered the color saturation to eliminate noise.

The Orion field flattener did a really good job of correcting field-curvature distorted star images across approximately 80% of the field of view. If you look close, you can see that the outer 10% on the right and left sides of the image contain slightly elongated stars. I could have cropped them out, or used one of the astronomy plugins for GIMP that have star rounding tools. But, in this case, other than some very slight cropping of the edges to remove stacking artifacts, I’ve opted to keep the full field-of-view image and not apply star-rounding correction.

Image Details
October 31, 2023 04:04:12-06:04:00UT
Two-hour time-lapse animation.
Minor Planet Center Predicted Vmags: (55) Pandora 11.6; (60) Echo 12.3
8 images, each a stack of 90 @ 10 seconds. Gain 350
FOV: 93.8 x 51.5 arcmin/1.56° x 0.86° (cropped size for animation)
North up. East left.
Seeing: Poor Transparency: Good Sky Condition: Bortle 7 with nearly full Moon 70° to the East.
Telescope: Orion ST-80 (80 mm f/5) + Orion Field Flattener + Baader Fringe Killer Filter
Camera: ZWO ASI482MC
Guide Scope: SVBONY SV165 (30 mm f/4)
Mount: Celestron CGEM
Captured with SharpCap Pro
Processed with Deep Sky Stacker, GIMP
Guiding: PHD2