A Supernova (SN 2023ixf) and a Quasar (3C 273)

 On 19 May 2023 the nearest supernova since 2014 appeared in the Pinwheel Galaxy (M101), which is 21 Mly (million light years) distant. It was first observed by Japanese amateur astronomer Kōichi Itagaki and reached a maximum brightness of magnitude 10.8 on 22 May.   

This supernova was designated  "SN 2023ixf".  The "ixf" part of the name is a base-26 numbering system used by the IAU (International Astronomical Union) for transient events.  This three-letter designation thus translates to i*676 + x*26 + f = 6714  (where i=9, x=24, f=6).  Automated survey instruments detect many thousands of supernovas each year in distant galaxies.  Most are too faint to be of general interest.  This supernova received attention in the scientific media because it was relatively nearby (in a cosmological sense) and was visible with modest telescopes and cameras.

M101 is a spiral galaxy located near the handle of the Big Dipper.

Location of M101 (red circle).  credit: SkySafariAstronomy.com

M101 and SN 2023ixf. E-M5iii + Rokinon 135mm f/2. ISO 1600, 60 s.  2° FOV.

This image was taken while M101 was high in the northern sky.  In the opposite direction in the constellation Virgo is another energetic object, the quasar 3C 273.  Quasars (Quasi-Stellar Objects) are supermassive black holes at the center of a host galaxy that release tremendous amounts of energy from the accretion of surrounding matter.  The name of this quasar derives from being entry 273 in the Third Cambridge (3C) Catalog of Radio Sources.  

Quasar 3C 273 (red circle).  credit: SkySafariAstronomy.com

 The measured redshift places this quasar and its host galaxy at a cosmological distance of 2.4 Gly (Billion light years).  This is 114 times more distant than M101 and about a thousand times farther away than the Andromeda Galaxy (M31).  With a visual magnitude of 12.8 this quasar is within reach of modest amateur telescopes (4-6 in or 100-150 mm), making it likely the most distant object in the universe that can be easily observed.

Quasar 3C 273.  E-M5iii + Rokinon 135mm f/2.  ISO 1600, 60 s.

 If 3C 273 were the same distance as the Andromeda Galaxy it would shine at magnitude -2.1 and would be the brightest star in the sky.  If it were the same distance as supernova SN 2023ixf it would shine at magnitude 0.65 and be the tenth brightest star, similar in brightness to Betelgeuse.

There are two 11th magnitude galaxies 1.25° east of 3C 273:

These two galaxies are about 50 Mly distant, or roughly 50 times closer than the quasar.

photo location: Creede, CO

The Moon occults Mars: 30 January 2023

 About one year ago on 30 January the Moon occulted (passed in front of) the planet Mars.  The event happened around 10 pm MST.  I was able to capture a sequence of images with an Orion 80mm ED f/7.5 refractor equipped with a field flattener and an Olympus E-M5iii camera.  The scope was riding on a Celestron CG-4 motorized mount.

At the time Mars had an apparent diameter of 10.8 arcsec and the moon phase was 9.8-d old waxing gibbous.

10:04 pm MST, about 4 minutes before contact.  ISO 400, 1/640 s.

Here is an animated sequence:

10:07 pm MDT, just before first contact.

Location: Santa Fe

As usual, click on an image to get access to the full-size version.

Last year's "Green Comet": C/2022 E3 (ZTF)

A comet designated "C/2022 E3 (ZTF)" was the third comet discovered in 2022.  It was picked up by the Zwicky Transient Facility (ZTF) at Palomar Observatory, a 48-inch Schmidt camera with a 605 Megapixel sensor array.  The comet made its closest approach to the sun on 12 January 2023 and it passed closest to Earth on 1 February 2023.  

Because of the possibility that it would achieve naked-eye visibility it was much hyped as the "Green Comet" in both the mainstream and astronomy press.  It reached a maximum brightness of about magnitude 5 - an easy target with binoculars but just barely visible to the naked eye at a dark-sky site.  The green color is a result of molecular de-excitation of diatomic carbon and cyanogen and is a common feature of most comets.

On any given night there are usually anywhere from six to a dozen comets within visible reach of small telescopes or astro cameras.  According to the Sky Safari app there are eight comets tonight (24 Jan) that could easily be photographed with my usual 135mm f/2 astrophotography lens. Other than flirting with naked-eye visibility, the so-called Green Comet was not unusual or particularly remarkable, in spite of all the hype.

All of the photographs below were obtained from my backyard in urban Santa Fe.

21 January 2023. 2° FOV.  E-M5iii + Rokinon 135mm f/2, ISO 800, 30 s.

As the comet neared Earth its motion was easy to detect over brief time intervals.  The two images in the animation below were obtained 54 minutes apart.  The sky brightness at the time was sqml=19.58.

26 January 2023. 2° FOV.  E-M5iii + Rokinon 135mm f/2.  ISO 800, 40 s.

27 January 2023. 2° FOV.  E-M5iii + Rokinon 135mm f/2.  ISO 800, 40 s.

At the time of closest approach the comet's motion was easy to detect.  The images in the animation below were obtained at approximately 1-minute intervals.  The sky was bright (sqml=15.2) with a 10.7-d waxing gibbous moon.  The comet was high in the northern sky in the constellation Camelopardalis.

31 January 2023. 1° field width.  E-M5iii + Orion 80mmED f/7.5.  ISO 1600, 30 s.

On 10 February the comet was on its way out.  Here it is passing through the line-of-sight near the overexposed planet Mars.

10 February 2023. 4° FOV.  E-M5iii + Olympus 75mm f/1.8.  ISO 1600, 30 s.

A quick test of the Astro-Tech 0.8x reducer/flattener

Refracting telescopes generally have curved focal surfaces.   When projected onto a flat sensor, star images become increasingly out-of-focus and smeared with distance from the center of the field.  This curvature can be mitigated with an additional optical element called a field flattener.  Some flatteners also incorporate a small amount of convergence which shortens the effective focal length and creates a brighter image.  These are called reducer/flatteners.

I did a quick test of a newly-acquired Astro-Tech 0.8x reducer/flattener (model ATR8) attached to an Astro-Tech AT72EDII refractor.  The reducer/flattener shortens the focal length from 432 mm to 346mm and the focal ratio is reduced to f/4.8 (from f/6).  The scope was mounted on a Celestron CG-4 motorized equatorial mount.

The camera attached to the flattener was a micro-four-thirds (17.3 x 13 mm sensor) Olympus E-M5. The back-focus spacing between the shoulder of the flattener and the image sensor was set to 55 mm.  A Bahtinov mask was used to ensure proper focus.

The 16-January sky was bright with normal city sky glow fortified with light from a 6.3-d waxing-crescent moon. There is a whole series of tests and comparisons that I would like to do, but it's winter and therefore cold and uncomfortable, so only three images were obtained.  More comprehensive tests will have to wait for better weather and darker skies.

Orion Nebula (M42).  1:1 crop from a larger image. E-M5, ISO 800, 30 s.

The full-size image (2x binning) with the cropped area outlined.

There are some power lines that cross the field of view in the above image and introduce diffraction spikes in the stars near the top.  I can also detect the trails of at least six satellites (probably Starlink).  It is becoming increasingly difficult to take astrophotos without being photo-bombed by satellites.

Sirius.  E-M5, ISO 800, 10 s, 2x binning.

 

A star field in Gemini.  The reddish star near the bottom is mag-3.3 Propus (Eta Geminorum). E-M5, ISO 800, 30 s, 2x binning.

 In the above image I was aiming the telescope with a laser pointer (difficult with a bright sky) and trying to get near the star cluster M35.  The aim was a bit off.  The chart below shows the region covered in this image.

credit: SkySafariAstronomy.com

The test was mostly successful.  The star images are acceptable out to the edges of the frame, with only some minor distortions.  An even more pleasing result is that the mount tracks well with no guiding for 30-s exposures (at least).

Solar imaging with a TS-Optics 50mm f/4 ED travel scope

 The TS-Optics 50mm travel scope is an f/4 doublet refractor with one "ED" (Extra-low Dispersion) element to minimize chromatic aberrations.  It is offered by Teleskop-Service Ransburg GmbH in Germany.  It is a modular scope with a Crayford focuser and can accept a wide variety of diagonals and eyepieces.   

For today's solar-imaging test, the scope was configured with a Lunt Solar Wedge, a Baader Solar Continuum filter,  a Celestron Omni 2x Barlow lens, and a ZWO ASI120mm-s camera.

The ASI120mm camera has a 4.8 × 3.6-mm 12-bit monochrome sensor with 3.75-μm pixels (1280 × 960).

The Solar Continuum filter is a narrow-band (10 nm) filter centered on 540 nm (green).  This filter eliminates residual chromatic aberrations from the atmosphere and telescope objective and works well with monochromatic sensors.

Images were obtained both with and without the barlow lens.  The Barlow lens element was screwed directly onto the camera nosepiece with a lens-to-sensor spacing of 42.5 mm.  The resultant amplification factor was 1.74.

With the Barlow lens.

 

Without the Barlow lens.

The present angular diameter of the sun is 0.542°.  Combined with the stated pixel dimensions this yields a telescope focal length of 213mm or f/4.3 for the actual focal ratio.

For comparison to these "back-patio" images, here is a same-day image from NASA's Solar Dynamics Observatory in geosynchronous orbit:

Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams

Santa Fe bright skies - another sparkle filter test

The sky was "clear" last night, a brief interlude between snow storms.  I could see stars, and no obvious clouds, but I wouldn't call it "dark".  The measured sky brightness was sqml=18.74.  This is about 14 times brighter than a nice dark sky (21.6) in Creede.

I wanted to try out the Hoya Sparkle 6x filter with a shorter focal-length lens, so I set up the Sony A7iii with a Samyang 24mm f/1.8 AF lens.  This lens has a convenient feature for astrophotography.  There is a button on the lens body that sets the focus to infinity if it is pressed while turning the camera on.  This saves time from having to mess around with getting the focus correct.

The image below was obtained using ISO1600 at 15 sec.  This was too much exposure for the sky brightness.  ISO800 would have been better.  A big adjustment to the black level was required to make it look like night.  According to Alyn Wallace the Sony A7iii is ISO invariant above ISO640, so that would be an even better setting.

I like the effect of this filter.  It will be interesting to do a comparison with the Hoya/Kenko Softon filter under truly dark skies.  

Sony A7iii + Samyang 24mm f/1.8 AF.  2x binning.

Sirius (Alpha Canis Majoris) and Murzim (Beta Canis Majoris).  12.5° field.

Orion.  22° field.

As usual, click on an image to get access to the full-size version.

More sparkle

The sky was clear, so I was able to get a couple more test images with the Hoya Sparkle 6x filter. Both were obtained with an Olympus E-M5iii camera and Sigma 30mm f/1.4 lens: 15-sec exposures (on a tracking mount) at ISO 1600.   Downtown Santa Fe is not the ideal location for doing wide-angle astrophotography.  The sky brightness measured after taking these two shots was sqml=19.42, more than six times brighter than a mediocre dark sky in Creede.  You can see the murk of city lights in the lower part of the Orion image. On the other hand, the temperature in Creede was 6° F and falling vs 31° F here.

Orion

 

The Hyades and the Pleiades.

Perihelion 2024

 Today the earth is at perihelion, the closest it gets to the sun during its yearly orbit.  The apparent solar diameter of 0.542° is 1.7% larger than average.

E-M1iii + AT72EDII + Lunt solar wedge + ND-0.9 filter.  ISO 200, 1/800 s.

A New Year and a new filter

 To my eye, wide-field astrophotography benefits from the use of diffusion filters.  These filters spread out the light from the point-source stars and produce a better depiction of relative star brightness.  Filters that I use are the Kase Astroblast, Tiffen double fog 3, and Hoya/Kenko Softon-A. The Softon filter is my current favorite.  All of these filters produce "round" star images.

I recently acquired a different type of filter, the Hoya Sparkle 6x.  This filter adds six diffraction spikes to concentrated light sources.  There is also a "Sparkle 4x" variation that adds four diffraction spikes.  The original motivation for trying this filter was get more "sparkle" in the photos of the Christmas tree.  But it also looks promising for astrophotography.

Constellation Auriga.  E-M5iii + Sigma 30mm f1/4 + Hoya Sparkle-6x filter. ISO 1600, 15 s.

The filter does a good job showing relative star brightness and also preserves color quite well.

Auriga is the home of three Messier-catalog open star clusters: M36, M37, and M38.

White circles: M38 (top), M36 (Middle), M37 (Bottom).

It looks like this filter will work best with  focal lengths 30 mm and shorter.  With longer focal lengths the diffraction effect is way over-done.  Here are two examples using a 75mm lens:

The Pleiades (M45). Olympus 75mm f/1.8 + Hoya Sparkle-6x filter.

Aldebaran and the Hyades Cluster. Oly 75mm f/1.8 + Sparkle-6x filter.

And yeah, I think it does a good job on the Christmas tree: