Imaging Two Pinwheel Galaxies

I found it interesting to compare images of two Pinwheel galaxies despite the difference in targets and imaging setups.

The Pinwheel Galaxy, M101 in Messier’s catalogue, is a beautiful face-on spiral galaxy that is popular with astrophotographers. Tonight at 11:00 pm from Vancouver, it is at an altitude of 84°- almost straight up – in the constellation Ursa Major. This is a great location for visual observing or imaging to minimize atmospheric disturbance.  I collected image data of M101 in 2014 with a small 100 mm refractor.

Another pinwheel from Messier’s catalogue is M83, also known as the Southern Pinwheel. It is visible at the same time but its altitude is just 10° above the southern horizon in the constellation Hydra when viewed from Vancouver. That location makes M83 a difficult target so I decided to use a remote telescope in Chile at latitude 30°S.  From Chile, M83 reaches 89° when transiting the meridian at 02:16 am UTC.

Click on the image to open a larger view.

Two very different setups were used to collect the imaging data. The M101 data was collected using my own equipment from Coquitlam, BC:

  • Skywatcher 100ED pro refractor
  • Nikon D5100 DSLR
  • Total Exposure:  30 min with 20 subframes at 90 sec and ISO 1600
  • Heavy light pollution (sqm: 18.5, Bortle class 7)

The M83 data was from the remote CH-1 telescope in Chile:

  • Planewave CDK24 (60 cm, F6.5)
  • FLI ProLine PL900 (3056 x 3056)
  • Total Exposure: 90 min with  9 Luminance and 3 each of Red, Green, Blue subframes at 300 sec and 1 x binning.
  • Pristine Dark skies at an elevation of 1500 m (sqm: 21.8, Bortle class 1) – same skies as the Gemini South telescope.

So it is not at all surprising that the M83 image is better with 6X more aperture and 3X longer exposure.

The two galaxies are both face-on spirals, appear somewhat similar, and are close to the same visual magnitude but some of their physical properties are quite different as shown in the table below.

ConstellationUrsa MajorHydra
Visual magnitude7.867.54
Angular Size28′.8 × 26′.912′.9 × 11′.5
Distance1.8 Mly14.7 Mly
Diameter170,000 ly55,000 ly
Radial velocity241 ± 2 km/s508 km/s
Number of Supernovae


M83 has spawned a large number of supernova explosions — six in total that we have observed (SN 1923A, SN 1945B, SN 1950B, SN 1957D, SN 1968L, and SN 1983N).  Only 4 supernovae have been observed in M101 but SN 2011fe, a Type Ia supernova, reached magnitude 9.9 in 2011 and was visible in binoculars.

M83 is thought to have a double nucleus at its core. The paper  “Double nucleus in M83” provides evidence of a second hidden nucleus that is more massive than the visible nucleus.

Nova Newsletter for May/June 2020

Our NOVA Newsletter for Mar-Apr 2020 is available as a pdf file. An archive of older issues can be found on our Newsletter page. The contents include:

A Close, Unheralded Neighbour by J. Karl Miller

President’s message by Gordon Farrell

AAVSO Custom Chart Plotter – A Game Changer by Robert Conrad

RASC Virtual General Assembly 2020 by the RASC Vancouver GA Committee

RASC Virtual General Assembly 2020 poster.
Schedule and more info at

A Springtime Collection of Comets

“The Hour arrived—and it became
A wandering mass of shapeless flame,
A pathless Comet, and a curse,
The menace of the Universe!”

Lord Byron, “Seventh spirit” from the dramatic poem Manfred, 1817.

Throughout history and across cultures comets have be viewed with dread, fear, and awe. They have been branded with such titles as “the Harbinger of Doom” and “the Menace of the Universe“. Nowadays, we look forward to observing them and hope for a comet bright enough to view with our naked eyes.

Comet C/2019 Y4 Atlas from Cqoutilam on April 14, 2020.
Comet C/2019 Y4 Atlas imaged from Coquitlam BC on April 14, 2020

This spring features a fine collection of bright comets. It is doubtful that any will reach naked-eye visibility so a small telescope or binoculars are recommended for observing them.

A comet’s brightness is measured on a scale called visual or apparent magnitude. The following table is a refresher on some common magnitudes for those not familiar with this scale. Notice the scale is backwards where small magnitude indicates brighter objects.

Venus (brightest planet)-4.6
Sirius (brightest star)-1.4
Polaris (the North Star)2.0
Naked-eye limit (city/urban)
Faintest star seen from a city location
Naked-eye limit (dark sky)6.0
Binocular limit9.0
Small Telescope limit (100 mm refractor)11.0

C/2019 Y4 Atlas

C/2019 Y4 Atlas had stargazers looking forward with anticipation to the next great naked-eye comet. Its rapid brightening in Feb 2020 led to speculation that it would become a naked-eye comet that might even be visible in daylight.

“a comet may be visible with the naked eye in late April and early May. It’s even possible that it could get bright enough that it’s visible at twilight while the sun is still up”


But it was a bit of a let down to learn that images taken in early April showed its nucleus starting to disintegrate.

This image, taken on April 20, 2020, shows fragments of C/2019 Y4 (ATLAS). Image credit: Quanzhi Ye & Man-To Hui.
An image taken on April 20, 2020, shows fragments of C/2019 Y4 ATLAS. Image credit: Quanzhi Ye & Man-To Hui

C/2019 Y4 Atlas is still relatively bright at magnitude 9.5 and is in a good position for viewing. It appears about 30° above the horizon in the northwest at 11 pm. It is headed lower and dimming so the next few weeks may be our last chance to observe it.

Graph showing correlation between the brightness of C/2019 Y4 Atlas and BC's COVID-19 cases.
Correlation between the brightness curve of C/2019 Y4 Atlas and BC’s COVID-19 cases

With tongue in cheek, one can see “evidence” that comet C/2019 Y4 Atlas was a “harbringer of doom”: It appeared and started to rapidly brighten just before the number of cases of COVID-19 in BC started to ramp up; The comet’s peak brightness corresponds closely with the peak of COVID-19 cases; and The curves for the comet’s brightness and the number of new COVID-19 cases have both shown signs of flattening. Perhaps its recent dimming should be interpreted as a foreshadowing that the worst of COVID-19 is over 😉

C/2020 F8 SWAN

Comet C/2020 F8 SWAN may be the brightest comet of 2020 – if you able to observe it from the southern hemisphere. It is already bright at 7.0 mag and is expected to brighten to magnitude 3.5 as it continues to approach the Sun during May.

Comet C/2020 F8 Swan
Comet C/2020 F8 Swan with its striking ion tail. Featured as the APOD on April 29th, 2020 . Image Credit: Gerald Rhemann

It has developed a striking tail. In the Northern Hemisphere, it is only visible extremely low in the sky in late May. It will re-appear in the morning sky in August but by then is expected to have dimmed down to mag 11.

C/2017 T2 PanSTARRS

The comet C/2017 T2 PanSTARRS has been a steady performer. It became brighter than mag 10 on New Year’s Day 2020 and is currently at magnitude 8.2 as it makes its way from Camelopardalis toward the Big Dipper. It reaches perihelion, its closest point the Sun, on May 4th.

Comet C/2017 T2 PanSTARRS
Movement of Comet C/2017 T2 PanSTARRS on Nov 20th, 2019 from Coquitlam, BC.

It is expected to be at its maximum brightness of 8.0 on May 15th. For a special treat, a few days later on the nights of May 22nd and 23rd, the comet will pass within 2° of the galaxies M81 and M82. It should remain bright until July and is well-positioned for viewing from Vancouver during the next few months.

Chart for C/2017 T2 PanSTARRS close to Bode's Galaxy M81 on May 22 at 23:00
From Vancouver C/2017 T2 PanSTARRS will appear close to Bode’s Galaxy M81 & the cigar galaxy M82 on May 22 at 11:00 pm

On June 4th, the comet will be easy to find as it passes less than 1° from Dubhe, the brightest star in the Big Dipper.

C/2020 Y1 Atlas

Another comet that is well positioned for observing from Vancouver is C/2020 Y1 Atlas. It is following a similar path to C/2017 T2 PanSTARRS, heading higher in Northern sky.

Comet C/2019 Y1 Atlas
Comet C/2019 Y1 Atlas on April 14th, 2020. Image credit: Roland Fichtl
Light Curve for Comet C/2019 Y1 Atlas
Observed and Predicted Light Curves for Comet C/2019 Y1 Atlas from

It is currently around 7.9 mag and has continued to brightening even though it reached perihelion on Mar 15. Its observed brightness has consistently being higher that the initial predictions as shown in its light curve where blue and black dots are visual and photometric CCD observations from COBS or the MPC, and the gray curve is based on the original MPEC or MPC predictions. Software like Stellarium and SkySafari appear to be displaying the magnitude for this comet from the initial predictions – as a result, the comet might appear much brighter in the sky than it does in the simulated views from the software.

Lets hope it stays bright longer as it will be within 0.5° of the Owl Nebula M97 and within 2° of the galaxy M108 on May 25 at 11:00 pm PDT as seen from Vancouver – that should make a nice photo op.

Chart for comet C/2019 Y1 Atlas near the Own Nebula M97
Stellarium Chart for C/2019 Y1 Atlas near the Owl Nebula M97 on May 25, 2020 at 11:00 pm as seen from Vancouver. The red circles have diameters of 0.5° and 2°.

How Close was Asteroid 1998 OR2?

The large asteroid 1998 OR2 safely made a close flyby of Earth on April 29, 2020. Its size is estimated to be between 1.8 and 4.1 km, making it capable of doing some serious damage and NASA classifies it as a large “potentially hazardous asteroid”. But its orbit has been carefully tracked and this asteroid poses no possibility of impact for at least the next 200 years. How close did it come? I tried to find out by measuring its parallax from two remote observatories and applying my rusty high-school trigonometry – the result was a distance value within 0.8% of NASA’s estimate.

Slooh hosted a live viewing of this asteroid on April 28. 2020 just before its closest flyby of Earth. They had two of their remote telescopes pointed at the asteroid: one located in the Canary Islands and another near Santiago in Chile. As expected the position of the asteroid, with respect to the background stars, appeared to shift in images taken by each telescope. This image shift is known as parallax. To make the shift more obvious, I grabbed an image from each telescope and aligned them with the Gimp (free image processing software similar to Photoshop). The asteroid appears as a slightly elongated oval compared to the background stars because of its rapid apparent motion during each exposure.

Image shift of the asteroid in two overlaid images: One from the Slooh Observatory in Chile and the other from their Observatory in the Canary Islands.

I noticed that the angular distance of the shift is about the same as the distance between a couple of stars just above the comet. So I fired up Stellarium and used its Angle Measure tool to measure the distance between the two stars. This turned out to be 4’ 30.84” or 0.0013131 when converted to radians.

Angular Distance Measurement in Stellarium between two stars

With that measurement, the distance to the asteroid can be calculated with a bit of parallax math. The animated image below illustrates how the asteroid can shift in position with respect to the background stars when observed from two separated sites.

Parallax is the shift in the position of an object relative to the background stars. Image Credit:

The geometry for our case is shown in the not-to-scale diagram below where the circle represents the Earth. Notice that the observing sites in the Canary Islands and in Chile are separated by less than the diameter of the Earth.

Parallax Geometry for Calculating the Distance to the Asteroid.

We want to calculate d – the distance to the asteroid. The definition of the trig tan function, tan(p) = r / d, can be re-arranged as

d =  r  /  tan(p)

to do so.

The parallax angle, p, is known from our prior use of Stellarium’s Angle Measure tool – it is 1/2 the measured shift in the asteroid’s position or ½ * 0.0013131 = 0.0006565 radians.

The value of r is 1/2 of the chord length between the Slooh observatory in Chile and the observatory in the Canary Islands. The arc length, a, between these two sites (along the surface of the Earth) is easy to find, Google reports it to be about 8912 km. The general formula for calculating the length of a chord from an arc-length on a circle is

chord_length = diameter * sin( arc_length / diameter )

The circle, in this case, is the Earth whose diameter, ed, is approximately 12,756 km. That allows us to calculate r:

r =  cord_length  / 2
= ed * sin(a/ed) / 2
= 12756 * sin(8912 / 12756) / 2
=  4,102 km

Plugging these values of p and r into the parallax equation provides an estimate of the distance, d, to the asteroid.

d =  r / tan(p)
= 4102 / tan(0.0006565)
= 6,248,285 km

This value is within 0.8% of NASA’s estimate of 6.3 million km for the distance at closest approach – not too bad.

When observed from a single site, asteroid 1998 OR2 appears to move quickly across the field of background stars because it is relatively close to Earth. The animation below shows how much the asteroid moved during a 20-minute interval when observed from the Canary Islands Observatory.

Animation of the Asteroid’s Movement over a 20-minute interval from the Canary Islands.

I believe that the velocity of the asteroid could be calculated from this animation along with the distance estimate.  Is anyone up for tackling that calculation?

The Accelerated Season Finale of Sirius

by Milan B.

All non-circumpolar stars have seasons of visibility. They depend on how far the star is from the Equator (the declination), but also how far the star is from the ecliptic. Sirius, being a Southern Hemisphere star and lying around 17 degrees below the equator also lies quite a bit below the ecliptic. This celestial geometry results in Sirius’ visibility season stretching roughly between September 1st and May 1st (the following year) for observers near 49 degrees North.

So, we have a few days left for this year’s season and to many it may be obvious how fast Sirius is disappearing in the SW sky twilight these days. All non-circumpolar stars are rising and setting just under four minutes earlier each day, throughout the year, but is this season finale unfolding faster for Sirius than other stars? 

The end of season for Sirius coincides with another celestial phenomenon, this one by our own star – the Sun. Around this time of the year the days are lengthening at fast pace as we just past the spring Equinox in March. The sunsets are falling about a minute and a half later each day in April as the Sun is climbing higher in the Northern Hemisphere heading towards the June Solstice. The table below shows how the difference between the time Sirius sets and the sunset shrinks dramatically in the month of April.

DateSirius Setting atSunsetDifferenceAltitude of Sirius at
April 123:5719:454h 12min23.7o
April 1123:1720:003h 17min21.3o
April 2122:3820:152h 23min17.2o
May 121:5820:281h 30min11.6o

How dramatic the change is between April 1st and May 1st could be seen in the images taken from Sky Safari. Both images show the SW-W sky at the time of civil dusk, when the Sun is about 6 degrees below the horizon and when the brighter stars become visible.

On April 1st the altitude of Sirius at Civil dusk is 22.4o

On May 1st the altitude of Sirius at Civil dusk is only 6.1o

In normal times I would say: go out and enjoy the last few days of Sirius visibility in the evening SW sky, but we are in different times. Hopefully, next year in April, we will be able to do this without breaking any rules.

Yuri’s Night – Celebrating the First Human in Space

Cosmonaut Yuri Gagarin became the first human in space on board Vostok 1 on the morning of April 12, 1961.

Yuri Gagarin – 1st human in space

The event is celebrated as Yuri’s Night around the world each April. The 2020 celebration is a virtual World Space Party at due to the covid-19 pandemic. The Yuri’s Night webcast on youtube will connect Yuri’s Night fans around the world to dozens of astronauts, celebrities, musicians, space professionals and more in a huge celebration of humanity & human spaceflight worldwide.

“Circling the Earth in my orbital spaceship I marveled at the beauty of our planet. People of the world, let us safeguard and enhance this beauty — not destroy it!”

— Yuri Gagarin

Cosmonauts were chosen not only for their excellence in training but also for their short stature because the cockpit was small. Gagarin was 1.57 meters or 5 feet 2 inches tall.

Legend says that Gagarin had to relieve himself on the way to the launch pad. Modern (male) cosmonauts have done so as well: They leave the bus and relieve themselves at the left back wheel of the bus. A new space suit design might mean and end to this tradition.

Vostok 1 made one complete orbit of the Earth that took 108 minutes. The first American in space was Alan Shepard’s aboard the Freedom 7 Mercury capsule. Shepard’s craft entered space, but was not capable of achieving orbit.

Vostok I capsule used by Yuri Gagarin in first space flight. Now on display at the RKK Energiya Museum outside of Moscow.

Gagarin ejected from the space capsule when it was still 7 km from the ground. He then deployed a parachute at 2.5 km in altitude.

A farmer and her daughter came upon Gagarin after his landing. Dressed in his orange spacesuit and dragging his parachute, he told them “don’t be afraid, I am a Soviet like you, who has descended from space and I must find a telephone to call Moscow!”

A crater on the Moon is named for Gagarin, as is asteroid 1772 Gagarin.

The following infographic from has more on how the first human spaceflight worked.

Astrophysics In Depth

Have you got some time on your hands? Tired of watching superficial youtube videos? Want some more depth in your knowledge of astronomy?

The Australian National University has 4 free on-line courses organized into a astrophysics xSeries that is offered on-line on the edX platform.

I have gone through two of the courses and can vouch for their high-quality. They have an awesome tag-team of instructors – one is a Nobel laureate and the other an award winning professor and educator. These are superbly crafted courses, filled with interesting details on the techniques, research, knowledge and remaining mysteries of astrophysics. Both instructors are highly qualified, to say the least, and obviously enjoy their work. They have a knack for clear communication and plain speaking and make complex topics understandable. Anyone taking these courses will not just learn a lot about astrophysics, but also about the thought process used by astrophysicists in tackling the mysteries of the universe. 

The courses in the series are:

Astrophysics: The Violent Universe
Image Credit: NASA Hubble

Greatest Unsolved Mysteries of the Universe: This course will take you through nine of the greatest unsolved problems of modern astrophysics. We don’t know why the Big Bang happened. We don’t know what most of the universe is made of. We don’t know whether there is life in space. We don’t know how planets form, how black holes get so big, or where the first stars have gone. Learn what we do know and don’t know, and get an up-to-date understanding of current research

Image Credit: Credit: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC)

Exploring Exoplanets: Explore the mysteries of exoplanets – planets around other stars. The discovery of exoplanets is one of the greatest revolutions in modern astrophysics, with the finding that the universe is teeming with planets. They are a strange bunch, from hot Jupiter-like planets skimming the surfaces of their stars to cold and lonely free-floating planets far from any star, and even planets orbiting neutron stars. This course will bring you up-to-date with the latest research on exoplanets, and how it has revolutionized our understanding of the formation of solar systems like our own.

Image Credit: NASA GFRC Dana Berry

The Violent Universe: Covers the deadliest and most mysterious parts of our universe, such as black holes that warp the fabric of space and time; or white-dwarf stars and neutron stars, where the laws of quantum mechanics collide with relativity. The course also covers dwarf novae, classical novae, supernovae and even hypernovae: the most violent explosions in the cosmos.

Galaxy superclusters in the nearby universe. Image credit: Richard Powell CC-BY-SA-2.5

Cosmology: the study of the nature of the entire universe, its origin, and its ultimate fate. Where did it come from? How will it end? What is the nature of space and time? Learn how recent advances give precise, reliable answers to many cosmological questions but still leave many of the most fundamental mysteries unsolved.

This might be your only chance to take a course from a Nobel Prize winner! One of the instructors, Brian Schmidt, shared the 2011 Nobel Prize in Physics with Saul Perlmutter and Adam Riess for providing evidence that the expansion of the universe is accelerating.

The other instructor is Paul Francis, an ANU professor and distinguished educator. He was awarded the 2016 Australian Award for University Teaching and Award for Teaching Excellence. Notable guest speakers, such as Lawrence Krauss and Brian Cox, make appearances to help you explore the theories behind modern cosmology and astrophysics.

Verified certificate available for a small fee.

These courses are designed for people who would like to get a deeper understanding of these mysteries than that offered by popular science articles and shows – one course can take 8 to 9 weeks if you devote 3-5 hours per week to it. Anyone can take the courses for free – you get the sheer joy of learning and can even skip out on the quizzes and assignments. Or you can pay a small fee and earn a certificate provided you get a mark of 70% or higher.

The courses are self-paced so they can match your schedule. Each is delivered as a set of videos with short quizzes between the videos to test your understanding. There are handout notes, a discussion forum, homework assignments and a final exam – just like an in-person college class. A cool on-going mystery project helps you experience what it is like to be a research astrophysicist. The project gives out clues, data, and discoveries about a made-up universe, very different from our own, after each section. These are discussed and you are challenged with developing an understanding and theories about this new universe.

You will get the most out of these courses if you have done math and physics in high-school and are willing to put that knowledge to work. Most of the math is “back-of-the-envelope” calculations that can be done on a note pad. But you can still learn a lot by skipping the math and just watching the videos.

Unwind under a Clear Dark Sky Tonight

Clear skies are in the forecast for tonight. Take some inspiration from a message, sent out by the International Dark Sky Association, to get out and unwind under a dark sky.

Photo credit @Alivia Dey — at West End, Vancouver.

Many of us are facing new anxiety and fear due to the uncertainty and enormity of what we are experiencing together. Studies have demonstrated how just ten minutes in nature brings benefits to our health and wellbeing. Dark Sky supporters often share stories about the rejuvenation they feel under the stars. Taking a few moments to look up at the sky at the end of the day – whether from a window, balcony, back yard, or park – can help lift the spirits and remind us that we are all connected under one big sky.”

Ruskin Hartley, International Dark-Sky Association

You might like to start early by applauding our health care workers at 7 pm then wait for the skies to have darkened by 9pm. Try turning off any unnecessary lighting to help reduce light pollution and help everyone get a better view of the celestial wonders.

Venus will be brilliant in the West.  Orion and the Orion Nebula (if you have binoculars) will be in the south-west. The brightest star in the sky, Sirius, is a little more to the south.  If you have a telescope then comet ATLAS is in the North and getting really bright fast – check out Tim Yaworski’s youtube video about this comet. Tim is a RASC Saskatoon member.

Nova Newsletter – Mar/Apr 2020

Our NOVA Newsletter for Mar-Apr 2020 is available as a pdf file. An archive of older issues can be found on our Newsletter page.

Contents of Volume 2020, Issue 2, Mar-Apr 2020:

  • General Assembly Vancouver 2020 Update by Hayley Miller
  • International Women’s Day Girl Guide Event by Hayley Miller
  • President’s Message by Gordon Farrell
  • Can We See the Whole Universe by Andrew Krysa
  • My First LPA (Light Pollution Abatement) Report by Leigh Cummings
  • Are the Weather Gods Mad at Us? by J. Karl Miller