Observing Saturn and Jupiter in 2021

Saturn and Jupiter will be well placed for observing in the second half of the summer and into the Fall. DDOD Astronomers Dr. Ian Shelton and Dr. Tuba Koktay recently obtained images of the two planets using their 10-inch telescope from Richmond Hill in Ontario. The first image shows Jupiter with its Great Red Spot visible. The second image taken two hours later clearly shows how quickly the planet rotates. The third image displayed at the same scale as the first two images shows how Saturn’s much greater distance makes it look much smaller than Jupiter in telescopes, even though the two planets are actually similar in size.

On the night of August 1, 2021, Saturn will be at “Opposition”, meaning that it is as close to exactly opposite (180 degrees away from) the Sun as its orbit and our view of it from here on Earth allows. Observationally, Saturn will rise near sunset, set near sunrise, and be at its highest point in the sky as it passes due south (“transits”) at local midnight. As seen from Richmond Hill (and for much of the GTA), Saturn will rise at 20:35 EDT, sets at 6:14 EDT, and transits at 1:25 EDT.

Being at opposition also means that Earth is passing at its closest point to Saturn as the two planets travel along their respective orbits around the Sun. On this night, Saturn will be only 1.3367 billion kilometres away from us. Ok, not exactly what most people would consider “close”. But this is when Saturn appears largest in our telescopes, though still only about 18.6 arcsec in diameter (~100 times smaller than the full Moon). That’s for the ball of the planet; the rings extend about 1.3x further outward from the planet, spanning 43 arcsec. But the rings are never seen fully face-on and are currently tilted by about 18 degrees from being seen edge-on, making the rings look only ~13 arcsec wide. With an adequate telescope (at least a 75 mm lens or mirror, operating at 100x or more) and good atmospheric “seeing” (stability), this allows the southern hemisphere of the planet to now be partly visible again after having been blocked from view when the rings were near their maximum tilt of 27 degrees four years ago. We are currently seeing mostly Saturn’s northern hemisphere. But don’t expect to see any details on the ball of the planet: Saturn rarely shows anything but subtle bands wrapping around the planet.

On the night of August 19, 2021, it will be Jupiter’s turn to be at Opposition. Being 19% physically larger and orbiting at half the distance that Saturn orbits from the Sun, Jupiter will display a disk 49.1 arc-sec in equatorial diameter, more than double the apparent size of Saturn. And during Oppositions, Jupiter appears 25% larger than its average size as viewed from the Earth. The planet will be 600 million kilometres away from us on this night. Unlike Saturn, a modest size (~75mm) telescope is enough to reveal the bands and belts that perpetually define the upper layers of Jupiter. And even a good pair of binoculars will reveal Jupiter’s four largest moons, rearranging themselves into a different configuration each night as they orbit around the planet in just a few days. Three of these are larger than our own Moon.

Jupiter is easy to find in the night sky, looking brighter than any star. Saturn may prove a bit more challenging because it is 15 times fainter; but it is still about as bright as the top ten brightest stars in the sky, and so reveals itself by looking out of place if you know your constellations. The first sky map shown below will help you find the two planets this summer. It should match the sky if you are looking at around 11 pm in mid-August. If you are looking earlier in either the month or in the night, the planets and surrounding stars will appear further towards the East (E); if you are looking later in the night or the month, look for the planets further towards the West (W). The second sky map shows the region centred on Saturn at the time of its opposition (at 1:25 EDT on August 2).

To learn more about Saturn and Jupiter, have a look at the following websites:



Wishing everyone clear skies,

–Ian Shelton

Happy 86th Birthday DDO!


The David Dunlap Observatory’s official opening was on 31 May 1935, also Prof. Chant’s 70th birthday. The opening ceremony was attended by notables such as Sir Frank Dyson, and former Prime Minister William Lyon Mackenzie King, who praised the Observatory as “a gift to science all over the world.” Chant retired the same day and moved into Observatory House, the original pre-Confederationfarmhouse (built in 1864 for Alexander Marsh and known also as Elms Lea Alexander Marsh) just to the south of the administration buildings, where he spent his remaining years. In May 1939 the train carrying King George VI and Queen Elizabeth, the Queen Mother on their cross-Canada tour paused on the railway to view the Observatory and the largest telescope in the commonwealth. 

Presently, DDO has a rich heritage and offers public astronomy programs hosted by the City of Richmond Hill and provided by the program partners, DDODefenders and RASC.

To learn more please explore www.richmondhill.ca/Astronomy

-DDO Defenders : )

ISS passes Venus TONIGHT – and see Mercury too!

If you have a clear horizon, you can watch Venus setting about half an hour after sunset. And Tonight, the International Space Station (ISS) will appear to pass right above Venus at 9:36 EDT tonight. The ISS will be moving from left to right and will appear ~20x fainter than Venus. 

Note also that the much fainter “star” about 3 degrees above and a little to the left of Venus is actually the planet Mercury. Watch Venus move closer to it each night and then pass right beside Mercury on May 28.

-DDO Defenders

Great Ideas Speaker Nights: Searching for the First Stars at Cosmic Dawn

Great Ideas Speaker Nights with Dr. Omar López-Cruz on Saturday April 24th 2021 at 7:00pmEDT

Zoom link (Meeting ID: 850 1103 3763 Passcode: 653518)

We believe that the first stars in the universe formed about 200 million years after the Big Bang. Yet, we lack solid observational evidence about the timing of this epoch, called Cosmic Dawn.

The experiment SCI-HI is searching for the first stars at Cosmic Dawn by the detection of variations in the 21 cm Hydrogen line background as a function of cosmic time. Towards achieving our goal, we have sought radio quiet zones within Mexican Territory and have identified Isla Guadalupe in the Mexican Pacific Ocean 300 km off the Baja California Peninsula, as one of the best radio quiet zones in North America.

In this talk, Dr. López-Cruz will present the first SCI-HI results, some current improvements, and perspectives.


Dr. Omar López-Cruz is a Mexican Astronomer (M.Sc. & Ph.D.; Department of Astronomy, University of Toronto) who has worked on stellar classification and the evolution of galaxies in large density environments.

In 2014, he led an international team that proposed the cD galaxy Holm 15A as the host of the largest supermassive black hole (SMBH) in the local universe. In 2019, a German team led by Kianusch Mehrgan measured a mass of 40 billion times the mass of the Sun in Holm 15A, confirming the López-Cruz et al. conjecture. He also likes the popularization of Science. Recently he became the co-director of a book collection called La Biblioteca Científica del Ciudadano (The Citizen’s Scientific Library) aimed at encouraging the debate of scientific ideas in democratic societies. He appears on radio programs regularly and lectures widely on Astronomy and Scientific Affairs. He writes for magazines and newspapers in Mexico.

Zoom link (Meeting ID: 850 1103 3763 Passcode: 653518)

Great Ideas Speaker Nights: Supernova 1987A

Zoom link: Meeting ID: 826 0823 4950 , Passcode: 212094

Supernovae are among the most violent events in the Universe since the Big Bang. They are highly destructive. And yet, they are also largely responsible for creating and dispersing most of the elements that enrich the Universe we live in. Indeed, without supernovae, the Earth and Life as we know them would likely not exist. On February 24, 1987, the brightest supernova since the invention of the telescope was discovered by a Canadian astronomer working on a mountaintop in Chile.

Join Dr. Ian Shelton for a personal account of his discovery of Supernova 1987A and efforts to find the elusive neutron star “beast” that created the explosion.

Zoom link: Meeting ID: 826 0823 4950 , Passcode: 212094

Tom Bolton (1943-2021 )

With heavy hearts, we report the passing of Professor Emeritus Tom Bolton earlier this week.

Tom is probably best known for providing the first definitive evidence showing that Cygnus X-1 is a black hole using the David Dunlap Observatory’s telescope. He was also instrumental in drafting the City of Richmond Hill’s landmark light pollution abatement bylaw.

As a close colleague of ours, he will dearly be missed.

Please take the time to watch this TVO Science Café episode where Tom -alongside other notable DDO astronomers – explains the history of the DDO and provides a tour of the 74″ telescope (circa 1990).

-DDO Defenders

What’s Up in December 2020?

If you would like to follow the exciting Astronomical Events in December,  please register to our upcoming Virtual Up In the Sky DDO program. Our expert astronomers will be teaching you how to navigate the night time sky.

Please visit richmondhill.ca/astronomy to register and get more information about this program.

On December 21st Jupiter and Saturn will pass very close to each other, so close that you’ll need binoculars or a telescope to separate them. During the month of December these two gas giant planets can be seen just after sunset can be seen just above the south-west horizon. The attached video (animated GIF) shows how the two planets move each day during the month of December, then move apart after their closest approach on the 21st. Even if the weather doesn’t cooperate on the day of closest approach, it will be a fun sight to watch these two giant planets move each clear evening during the month of December.

-DDO Defenders 🙂

Mars in 2020

Every couple of years, Earth passes near to Mars. But because Mars’ orbit is quite elongated (“elliptical”), the distance between the two planets can get much closer every 15-17 years. This year was one of these closest approach years, with Mars just 62 million km away on October 6th. Ok, not close enough to ever worry about ever hitting Mars; but if you are in the business of sending spacecraft to other world, this is the best time to do so. And indeed, the US, China and the United Arab Emirates each launched their own mission to Mars this year, all expected to arrive there in February next year.  

Both planets, of course, are continuing to travel along their respective orbits about the Sun. As the Earth moves faster along its smaller inner orbit closer to the Sun, it overtakes Mars travelling in its more distant orbit, like race cars travelling along an oval racetrack. From our perspective here on Earth, as Earth overtakes Mars, Mars will be seen in the opposite direction from the Sun. Hence, we use the term “opposition” to describe these events. And if Mars is currently opposite the Sun, that means it rises in the East at sunset and will spend the whole night crossing the sky to set in the West at sunrise!   Mars continues to appear to the unaided eye as an unusually bright, orangey coloured “star” in the Eastern sky after sunset until the end of October. It will then begin to fade noticeably as the distance between the two planets steadily increases. Although it will rise earlier each night and stays high in the sky through the night, it will have dropped five-fold in brightness by Christmas time. So enjoy Mars now while it’s at its best! If you have a telescope, even a small telescope, this is your best opportunity to see Mars through your scope for the next 15 years!!! Here’s a sample of what our members have been able to achieve in 2020… 

-DDO Defenders 😁

The Orionids

The Orionids meteor shower peaks on the night of Tuesday October 20-21. This is a modest shower, producing about 20 meteors (“shooting stars”) per hour if you are viewing away from city light pollution. Of course, the sky needs to be clear. And expect to see less than half that number if you are observing from a moderately dark backyard in the suburbs. The crescent moon sets at around 9:30 pm on this night and so won’t spoil the view this year.  

It takes at least 15 minutes for your eyes to fully adjust to the dark so you can see the fainter meteors (…there are many more fainter meteors than bright ones). Turn off all yard lights and find a place that is shielded from seeing your neighbour’s lights or streetlights. Even looking at your phone’s display can cause you to lose your dark adaption and you will need another 15+ minutes in the dark to restore it. 

You will need to wait till about 10:30 pm EDT before any of these meteors will become visible. That is when the “radiant” for this shower rises above the Eastern horizon. If the sky is clear and you do indeed start your viewing right at 10:30 (till ~11:00 pm), you have a chance to catch an impressive “earth-skimmer” meteor, one that remains visible for a longer time as it streaks across a much longer path across the sky. 

To watch the Orionids or any other meteor shower, I strongly recommend you find yourself a fully reclining full length deck chair (Chaise Lounge) so you can be off of the ground and comfortably looking straight overhead without having to bend your neck. That is where you want to be looking, straight overhead to see the most meteors. The meteors will seem to be coming from a particular point in the sky, the shower’s “radiant”: whichever constellation the radiant lies in is how a meteor shower gets its name. In this case, the radiant lies in the constellation of Orion. But each meteor can be almost anywhere in the sky when it first lights up; and then it usually travels less than a quarter of the distance from horizon to horizon before it stops glowing.  

For those interested in knowing what an Orionid meteor is made of, you might be surprised to learn they are pieces of Comet Halley, which last passed by the Earth in 1986. Comets leave behind a trail of rock dust that fills the path they take as they orbit the Sun. Earth passes through that thin debris trail twice each year, producing the Orionid meteor shower in the Fall and the Eta Aquarids meteor shower in early May. 

-DDO Defenders 😄