25 years ago, in late August 1998, something interesting happened in Canadian atmospheric science:
A large Canadian scientific stratospheric balloon was launched from Saskatchewan on August 24, 1998. It was intended to have a flight lasting about 24 hours and stay relatively near its launch site. Instead, it went on an unexpected adventure across an ocean and into several countries’ airspaces. Fighter jets were tasked with taking it down. World news organizations covered the updates.
This is the MANTRA 1998 story.
What is a stratospheric balloon?
It’s a very large balloon, typically filled with Helium, that carries a scientific payload (instruments and support systems) weighing up to ~a tonne (1000 kg) into the stratosphere (15 to ~50 km altitude).
They can be as tall as the CN Tower observation deck!
Stratospheric balloons like MANTRA are much larger & complex than common weather balloons, which also are typically Helium filled and carry instruments into the stratosphere. But those payloads are very small and light: ~250 g. That makes MANTRA’s scientific sensor payload (~300 kg) about 1200 times larger. Some sensor payloads are even larger.
Eureka Weather Station balloon launch preparations.
MANTRA was 150 meters high or about the size of a 25-story building when at stratospheric altitudes.
Photo showing MANTRA98 being prepared for launch, overnight August 23/24, 1998.
The MANTRA balloon included a variety of instruments designed to measure ozone chemistry-related atmospheric gases. There were also systems for power and control of the balloon. Its gondola was 2 m × 2 m × 2 m in size, constructed using a light aluminum frame. The total payload weighed 630 kg.
Schematic of MANTRA gondola from Strong et al. 2005.
More specifically, MANTRA instruments sought to acquire:
Vertical profiles of: NO2, HNO3, HCl, CFC-11, CFC-12, N2O, CH4, temperature, and aerosol backscatter from balloon instruments.
Total columns of: O3, NO2, SO2, aerosol optical depth by ground-based spectrometers.
Two major aspects of seasonal change are weather and the “length of the day” — i.e., the number of sunlight hours.
The magnitude of this change depends on latitude. Near the equator, the amount of sunlight stays relatively constant. In mid-latitudes there’s quite a noticeable change in the length of daytime. In Toronto, for example, the amount of sunlight in a day stretches from 9 hours in the middle of winter to over 15 hours in the middle of summer. In the polar regions the change is even more dramatic. There are times when the sun never sets (“midnight sun”) and times when the sun never rises (“polar night”). The seasonal change in sunlight has profound impacts on the environment, animals and plants, and people.
I wrote an earlier post about sunlight changing over the seasons, motivated by my time doing fieldwork in the Canadian High Arctic. In this post, I wanted to look at the same topic more generally and create an interactive plot for people to explore.
Joseph Mendonca and I watch the sun rise late morning on Feb. 25, 2013 in Eureka, Nunavut (photo credit: Paul Loewen)
This interactive figure illustrates the number of sunlight hours there are at a various Canadian cities and locations.
You can select a location by clicking on the entries in the legend. There are tools in the top-left of the figure to let you zoom in and explore the data.
Why does this happen?
This happens because the Earth’s axis tilts the Polar Regions completely away from the Sun, and into complete darkness in winter, and tilts towards the Sun for part of the summer. During summer in the Arctic, the Sun moves in a circle across the sky once per day, never setting.
Over the course of the year in the Polar Regions, the Earth’s axial tilt creates Polar Night during winter and the Midnight Sun during summer. Credit: https://en.wikipedia.org/wiki/Arctic_Circle#Midnight_sun_and_polar_night
Here’s a fun trivia question to ask friends and family: on what day of the year do all places on the planet have the same length of a day? The length of a day is equal everywhere on the planet two days a year.** These days are called the equinoxes. You can see these days by plotting multiple sites and looking where they intersect. I’ve also added an option on the plot to show them as lines on the plot.
Also noticeable on the plot is that the length of the day is maximum mid-summer and minimum in winter. These dates are the solstices, when the tilt of the Earth is either fully towards or away from the Sun.
I hope this puts the changing daylight hours you experience in a new light.
Enjoy!
Sunset over Mississauga, viewed from downtown Toronto
** atmospheric refraction can slightly impact the equality of the daytime/nighttime on the day of the equinoxes.
Acknowledgements:
Thank you to the python community, which has developed and maintained the packages I use to make nice plots, i.e. bokeh, numpy, pandas, ephem, and pytz.
Where to buy the best masks has come up a couple times with friends, who saw me post pictures of myself at work with an N95 mask. This post shares the sources I’ve found.
I’m a physicist, not a physician. This post is not medical advice.
(TL;DR: I like these masks. Also these. These are really good but they’re pricey. They are all Canadian-made N95-equivalent masks.)
I live in Toronto, which isn’t have a good time with COVID. Hopefully the pandemic will be over soon. At the moment, I am not yet vaccinated and still have a few things to do indoors around other people — medical appointments, occasional in-person work stuff — so I wanted to get a high quality mask. I don’t own a car, so going from A to B is either transit or Uber. I also want to be ready with a good source of masks in case the pandemic isn’t quite over but I’m teaching on campus this fall.
In my U of T Scarborough office wearing a Canadian-Made N95 (May 3, 2021). Please excuse the pandemic hair…
I started a year ago with a simple fabric mask. Then I got a box of surgical masks. Those work well (e.g., Bartoszko et al., 2020), are fairly comfortable, and generally come at a reasonable cost. The really cheap ones can be kinda awful. But the cost of good quality ones isn’t too bad (~$0.35/each).
CBC Marketplace visited a U of Toronto lab that did some comparisons of mask types. Surgical masks came out on top (CBC article here). The type of fabric mask U of T provided to all its faculty, staff, and students? It was at the bottom of the rankings. So I’m not trusting my workplace-provided mask. Except maybe on top of a good mask, for the sake of fashion…
Cleaning the window of an atmospheric measurement instrument (Pandora) at UTSC (March 10, 2021). Photo Credit: Don Campbell, U of T Scarborough.
I found an unlikely source of Korean KF-94s, which fit really well because of their different design. It was much easier to wear glasses/sunglasses with them. This prompted me to start looking beyond surgical masks.
What I want:
greatest protection to the user — ideally N95 mask
clear provenance — ideally made in Canada with transparent standards and test results
good fit and comfortable — I had to try a few to figure this out
There are lots of masks online that come from China. Or that aren’t labelled with a clear company/origin. Or the company and product info can’t be found online. For example, most masks from Walmart.ca and Amazon. Also, 72hours.ca has KN95s and “Made-in-Canada” N95s but I can’t seem to find any info about the companies. That might be ok? It’s hard to know. I’d prefer to buy masks from a known manufacturer that meet high standards and post independent lab test results.
Chinese (KN95) and other ‘N95 equivalent’ masks sometimes fall significantly short of N95 standards (e.g., ECRI report, CBC tests). I did buy a few KN95s because that’s what I could initially find. It would be preferable to buy from a Canadian company that is transparent about its standards and testing.
Here are high quality Canadian N95 masks I’ve found:
Eclipse N95 Masks
Eclipse Innovations is a company that manufactures N95 masks in Canada. You can read about them and their mask standards on their website here.
The nose bridge forms a really good fit and has comfortable secure padding. The straps go around your head to keep it snug. They might feel too hardcore for casual use. But if you want to go all-in, I think this is a solid choice.
Eclipse N95 masks. Note the padded mouldable nose part in the third panel.
The name of the distributor company they recommend, HotZone, is a bit “on the nose”. But I had a good order experience and would recommend them:
The box contained 25 masks and each mask was individually sealed. That’s a nice feature.
(Supply + Protect is another Canadian website that carries the Canadian-made Eclipse N95 masks as well as surgical masks. But I haven’t used them.)
The downside is that the Eclipse N95 masks are expensive.
HotZone also sells surgical masks that look good and are much lower cost.
Dent-X & First Nations Procurement Inc. FN95s
This is my current favourite. They have a different shape from the other N95s I’ve had/seen. I find them the most comfortable of all the masks. I sometimes use a clip that came with my KF94s to connect the ear loops behind my head. This makes the mask fit snug.
They’re lower cost than the Eclipse masks. Though they still cost more than surgical masks.
It’s interesting to note that these purchases support the Canadian Cancer Society. In addition, the masks are made by a partnership between Dent-X and First Nations Procurement Inc. (FNPI), which is a Certified Aboriginal Business with manufacturing facilities in Northern Ontario reserves (story). Sounds great all around.
Vitacore CAN95 masks
These have the best branding (“CAN95” with a nice maple leaf logo). The company seems good and were recently featured on CBC (article and video). I find them comfortable, though not as good as the other two above. They sell them in the ear-loop version or the headband style (like the Eclipse model).
N95s get pricey if you wear them everyday. I don’t. I use one or two a week, when I’ll be around people indoors without distancing at times. I consider that cost worth it for the peace of mind that I’m doing everything I can do to stay safe (and because I can afford to). If I’m doing something where there is minimal exposure potential, e.g., a brief trip inside a cafe to pick up a coffee, I’ll wear a surgical mask or the more comfortable Dent-X N95, and I might hang it somewhere in isolation for a week before re-using it. It’s worth noting: don’t wash an N95 with soap and water since this diminishes the charge layer (Juang & Tsai, 2020).
If you have a good source of masks or tips, comment below!
A couple months ago, on Sept. 27, there was a global climate strike.
I didn’t attend.
I had to teach classes, despite many colleagues (including me) signing an open letter to U of T asking classes to be cancelled (Varsity article). It turned out to be a valuable opportunity.
U of T did suggest that instructors avoid penalizing students for attending the climate strike. I announced that there would be no penalty for not attending that day. About half the class didn’t show up, hopefully deciding to contribute their voice to the event.
I guessed that the students who *did* come to class instead of attending the climate strike were more likely to be skeptical about climate science and the significance of the issue. At the start of lecture, I opened the floor to any questions about climate science.
Not being at the event put me in the room with one of the most important audiences: people who are *not* already persuaded that climate science is robust and that action is needed. It was a good opportunity to engage with them.
There were definitely some skeptical of the science and humanity’s contribution to climate change. Students were quiet at first, but after a couple of people asked questions, e.g., the evidence of actual warming, more questions started to flow.
I was told some didn’t feel comfortable asking initially because they expect to be scolded for having the “wrong” opinion. Once it became clear that I wasn’t judging them and having a genuine Q&A, the session became interesting and more students got involved. We used the hour.
I’m mentioning this now at the end of term because this started an ongoing conversation with a few students, who came to me after lectures and at office hours throughout the term asking more questions about climate science.
I didn’t try to persuade them to support a specific policy or accept a specific idea. But I did push them to think critically about the skeptical claims and to talk to people in the field when they have questions. There are many that generously make themselves available.
I was initially disappointed I couldn’t be at the climate strike. But in the end, I’m happy with how not attending turned out because of the engagement it created in some skeptical students.
Several of my photos have been featured in the Blackwood Gallery’s newly-published broadsheet, Society for the Diffusion of Useful Knowledge (SDUK) Volume 4: Grafting. A PDF copy of the full publication is online here.
The vision of the SDUK project is:
“To productively collide with the present crisis, ideas cannot be constrained by disciplines. An ecology of knowledge based on the relationship and antagonism of “useful” ideas will be composed and circulated through THESOCIETY FOR THE DIFFUSION OF USEFUL KNOWLEDGE (SDUK). The name of this innovative platform is borrowed from a non-profit society founded in London in 1826, focused on… spreading important world knowledge to anyone seeking to self-educate…”
There are some interesting pieces in the issue. My favourite is by Skye Moret, who presents the colour pallet of Antarctica in a visually stunning and fascinating way. A version of her piece is also on her website here.
The printed publication has been distributed at libraries, bookstores and communities centres in the GTHA and across Canada.
Assistant Professor (Teaching Stream) at the Department of Physics and Environmental Sciences (DPES), University of Toronto Scarborough.
This job is an amazing fit for me.
Here’s a few reasons why:
Academia
I’ve wanted a job in science. But I don’t only want to do science. I want a job that enables me to teach and do public outreach in a meaningful way. I spent a great deal of time and effort over the last decade working in education through NGOs, companies, and at U of T in a variety of roles. I also have a teaching degree. This position is teaching-focused, which is great, in addition to allowing me to continue to do research.
As an academic, I’ll also be able to continue doing science advocacy. Many of my former colleagues have gone to work for government science departments, such as Environment and Climate Change Canada (ECCC). It’s a nice career path, with stability and important work. But public servants are limited in their ability to criticize government policy, which I’ll be free to do. Given the continuing struggle to keep facilities like PEARL funded, the overall lack of ambition on many science topics, this privilege will be put to good use.
Dan discussing science engagement at U of T’s Rawtalk Live event (May 30, 2018).
Downtown U of T vs. Scarborough
I’ve spent the last 15 years living and working near downtown. The U of T downtown campus (UTSG) location has clear advantages. There’s an appealing energy and convenience to being close to the core of Canada’s largest city.
Royal Ontario Museum
But I wanted a change. I grew up essentially across the street from the Ottawa Greenbelt, and spent the warmer months of the year camping and cottaging in the surrounding rural areas of Ontario. Downtown Toronto doesn’t have enough greenspace. I spent the last several years living next to High Park. It was a great way to find balance. The U of T Scarborough campus has a strong environmental focus and is adjacent to a large forest, which is immensely appealing.
Leaf in High Park on a rainy day
I’ve moved to the east end of Toronto (Upper Beaches), and aim to do part of my commute by bike in the warm months, since there are trails that run from UTSC to GO Transit stations. That’ll be much nicer than biking along College St. to downtown U of T!
UTSC location (from Google Maps). Lake Ontario is at the bottom-right. Red marker shows where I’ll be working.
I have to admit one big downside: public transit in Scarborough is badly inadequate. I’m now enthusiastically cheering for Toronto (& other transit-funding levels of government) to build the Eglinton LRT line out to UTSC.
Interdisciplinary department
I’m not joining a physics department. DPES is a mix of physics, chemistry, astronomy, and environmental sciences. That’s also a quick way to summarize my academic background. I did my B.Sc. in astronomy & astrophysics, my M.Sc. in physics, and my Ph.D. in physics with a collaborative program in environmental studies. I’ve also spent considerable time engaged with environmental policy topics. I’m looking forward to interacting with colleagues across these fields. Ideally, I’d like to build a course or two that crosses disciplinary boundaries.
Experimental physics and environmental issues
My specific areas of focus will be exactly my areas of core interest: experimental physics and environmental connections to physics. One of the first large tasks I’m undertaking is a complete re-building of the undergraduate physics laboratory courses. I’m thrilled – this is exactly the type of project I’m keen to do. I’ll also be creating a course on atmospheric physics. Other ideas are floating around, too, but I should leave something for later blog posts.
Dan adjusting beamsplitter door of the PEARL 125HR spectrometer during the 2015 ACE/OSIRIS validation campaign.
Summary
I expect to be (very!) busy for the next few months (years?) as I get started with this exciting new chapter in life. There are challenges ahead. But I’m proceeding with enthusiasm. I’m joining a great institution and department. I’m still close enough to collaborate with my friends downtown at U of T and at ECCC. And if I need the excitement of downtown Toronto, there’s always the weekends.
It has been a long road, but I have at last reached a significant milestone:
I’ve finished my Ph.D.
Working towards this goal at U of T’s Physics Dept. has been a difficult but rewarding experience. I’m thankful to many people. My supervisor, Prof. Kim Strong, especially, as well as my fieldwork teammates. Graduate school is an opportunity to grow and change. I’ve tried to make the most of it. I thought I’d reflect on a few highlights.
Fieldwork at PEARL
Travelling to the frozen northern edge of Canada each winter to maintain and operate instruments at the end of Polar Night was an incredible experience. (Part one of my articles about the campaigns for U of T News; a Virtual Tour of PEARL slideshow.)
Dan looks through boxes of equipment at the start of a PEARL campaign.
Spending a month at a time in an extremely remote and cold environment isn’t for everyone. But it was a great fit for me. I have developed a great affection for Canada’s Arctic.
Volodya and Dan carry Brewer spectrophotometer to the roof of the PEARL Ridge Lab (photo credit: Pierre Fogal)
In addition to the opportunity to contribute to important research – the measurements we took during campaigns was used to study the Canadian Arctic atmosphere, but also contributed to international networks studying our changing global atmosphere and validate satellite measurements – it was also an opportunity to develop and apply my interest in photography. I am delighted that the photos I took while at PEARL have been used in national newspapers, on the covers of science journals, and more. It was great fun.
Dan Weaver taking photos on Ellesmere Island, in the Canadian Arctic (Photo Credit: Paul Loewen)
During my first trip to PEARL in 2012, funding for the lab was ended as part of systematic cuts to Canadian science. My longstanding interest in politics primed me to take action. I wrote letters to politicians, talked to the media, contributed to science advocacy organizations, and helped to organize science marches in Toronto.
Marching down major streets of Canada’s largest city was an exhilarating experience. Most of all, I met incredible people also advocating for science in Canada.
Dan kicks off the 2017 Toronto March for Science (photo credit: Paul Martin)
Sharing PEARL’s Arctic research with the public
I believe PEARL’s work is important. But until I was on Kim’s research team, I had never heard of it. Nor was I aware of Canada’s incredibly successful science satellite, the Atmospheric Chemistry Experiment (ACE). I tried to raise the profile of these research projects. I can’t claim all Canadians know about PEARL and ACE. But I’d like to think that my school visits in Ontario and Nunavut, dozen public talks, social media channels, and other efforts have broadened recognition of their importance.
Social media can be a fun way to highlight fieldwork. Even if it’s exchanging jokes about how Eureka resembles an ice planet in a galaxy far, far away…
Science is largely funded by the public. I believe scientists should actively seek to connect with the public.
Dan giving a Story Collider talk about PEARL fieldwork (photo credit: Ally Chadwick, @JustMyFreckles)
Travel to conferences
I travelled to two major international conferences during grad school: the 2014 American Geophysical Union (AGU) meeting in San Francisco and the 2018 European Geophysical Union (EGU) meeting in Vienna. It was gratifying to present my research. Connecting with researchers from around the world was eye-opening and inspiring.
A keynote at AGU by former-US astronaut and then-NOAA chief Kathryn Sullivan still occasionally surfaces in my head. She discussed how she saw NOAA as America’s ‘environmental intelligence’ organization, which I thought was an interesting way to frame its work. For some audiences, I imagine it is more effective than focusing on the inherent value of environmental protection and science – even though I find the latter persuasive.
Dan discusses PEARL water vapour measurement research during poster session
In addition to conferences, I attended meetings of an international network PEARL measurements contribute to, giving me the chance to visit Switzerland, Japan, and Korea. I spent two weeks exploring Switzerland and Japan after the meetings with a friend of mine, Nathan. We had a great time on both trips. Both times I was left with the clear realization that Canada has really poor rail system… (I write this while on a train between Toronto and Ottawa that is an hour late…)
Japanese Shinkansen train that travels at 300 km/hr. VIA Rail can’t even dream this ambitious!
Starting an environmental organization on campus
I greatly enjoyed the interdisciplinary conversations I had with people at the U of T School of the Environment, where I took a collaborative program. I created an organization to foster a sense of community amongst the grad students there, the Graduate Environmental Students’ Association. One highlight for me was inviting Jennifer Baichwal to do a Q&A at a U of T screening of Watermark, a documentary she produced that explored society’s connections with water in collaboration renown Canadian photographer Edward Burtynsky. We held a screening of Watermark and had a Q&A with her. The execution of that event happened after I left GESA; it was nice to be able to sit back and enjoy it once the day arrived.
Dan moderating a panel discussion about neonicotinoids for a GESA event at U of T
Teaching
Before grad school and my research internship at the Toronto Atmospheric Observatory (I have an interest in rooftop views), I took a degree in education and became an Ontario-certified physics and civics teacher. When I started grad school, I was keen to dive into duties as a Teaching Assistant. The department recognized my interest and qualifications and gave me opportunities to apply those skills as a Senior TA. I trained new graduate students in teaching and managed a large team of TAs for a first-year physics course.
Dan discussing science engagement at U of T’s Rawtalk Live event
Even more interesting, I co-created a pilot course connecting science students with entrepreneurship on campus. I worked with a Rotman School Prof. to give top U of T science undergrads a chance at applying their analytical skills on the real-world challenges faced by U of T startup companies. It was an good experience for everyone involved and it was a reminder to me that most students don’t go into academia after they graduate. I continue to believe we should do more to connect university undergraduate students with experiences and information related to non-academic career paths.
What’s next?
The journey was fulfilling, frustrating, and fun. I’d love to travel to PEARL one last time, but that’s unlikely. It’s time for something new.
I’m aiming to keep to keep engaged with the themes that defined my life over the last decade: physics and education, science and society, and interdisciplinary environmental issues. I’d like to fit in some music and outdoors time, too.
But where exactly I’m headed will be my next post. Onwards to 2019!
I was in Vienna mid-April to attend a science conference, the European Geophysical Union meeting. I had the chance to explore the city a bit. The fantastic transit system made it easy to visit the sights around town.
Days are getting longer everywhere in the northern hemisphere this time of year.* In the Arctic, the change in sunlight is particularly dramatic.
A few days ago, sunlight returned to Eureka, Nunavut for the first time since October, marking the end of Polar Night.
Joseph Mendonca and I watch the sun rise late morning on Feb. 25, 2013 in Eureka, Nunavut (photo credit: Paul Loewen)
During the transition between Polar Night and the continuous daylight of summer (“Midnight Sun”), a team of Canadian scientists take measurements of the changing atmosphere above Eureka at the Polar Environment Atmospheric Research Laboratory (PEARL) using specialized instruments.
(I was part of that team until recently. Daily updates from the campaign are posted here.)
Installing atmospheric monitoring instruments on the roof of the PEARL Ridge Lab during the 2014 sunrise campaign.
The return of sunlight after a long absence generates significant changes in the atmosphere. Ozone depletion chemistry, for example, is acutely impacted. A former colleague of mine wrote a blog about it here.
I made a few plots to show how big the sunlight shift is in high Arctic, with a few other locations included for comparison. This change in light has profound impacts on the environment, animals and plants, and people.
In Toronto (43°N), the amount of sunlight in a day stretches from 9 hours in mid-winter to over 15 hours in mid-June.
Sunlight hours each day in Toronto
The size of the seasonal change in sunlight depends on latitude. If you go south from Toronto, there’s less change over the course of the year. In the Caribbean, for example, a hypothetical province called Saskatchewarm would have relatively stable sunlight throughout the year:
Sunlight hours each day in the hypothetical “Saskatchewarm” in the Caribbean
Yellowknife, Northwest Territories (63°N) is much farther north than most Canadians venture. I recommend visiting it: there is fantastic art and culture to see. And it’s a good place to see Aurora Borealis. Since it’s 2000 km north of Toronto, it experiences a much larger swing in seasonal sunlight. It’s quite a big change: days in Yellowknife range from 5 hours in mid-winter to 20 hours mid-summer.
Sunlight hours each day in Yellowknife (2000 km north of Toronto)
From the North/South point of view, Yellowknife is roughly equal distances between the southernmost and the northernmost parts of Canada. The Canadian Arctic is a vast region. Let’s head another 2000 km north to look at daylight in the extreme case of Eureka.
Arctic landscape – Ellesmere Island
Eureka is a high Arctic research site at 80°N, on Ellesmere Island. The daylight hours plot is oddly shaped compared to southern sites. For most of the year, daylight doesn’t change day-to-day: it’s either totally dark or light.
Sunlight hours each day in Eureka
The transition between total darkness and never ending day takes only 2 months. This morning, the Eureka sunrise occurred at a rather convenient 10 am. It’ll set mid-afternoon. In a week, sunrise will occur more than an hour earlier, and sunset an hour later.
Rapid change in high Arctic sunlight
Sunrise at Eureka, Nunavut from the road to PEARL
Why does this happen?
This happens because the Earth’s axis tilts the Polar Regions completely away from the Sun, and into complete darkness in winter, and tilts towards the Sun for part of the summer. During summer in the Arctic, the Sun moves in a circle across the sky once per day, never setting.
Over the course of the year in the Polar Regions, the Earth’s axial tilt creates Polar Night during winter and the Midnight Sun during summer. Credit: https://en.wikipedia.org/wiki/Arctic_Circle#Midnight_sun_and_polar_night
If we combine the plots for all three sites, a couple of interesting dates pop out:
Sunlight at Eureka, Yellowknife, and Toronto
Here’s a fun trivia question to ask friends and family: on what day of the year do all places on the planet have the same length of a day?
The length of a day is equal everywhere on the planet two days a year.** These are the intersection points between the sunlight hours at Toronto, Yellowknife, and Eureka. If I added other cities, they would also intersect at those points. These special dates, March 20 and September 23, are when the Earth is facing the sun upright with no relative tilt. Day and night are both 12-hours long. (Another trivia question could be on what day are day and night the same length.) They’re called the equinoxes.
Also noticeable on the plot is that the length of the day is maximum mid-summer (June 21) and minimum in winter (December 21). These dates are the solstices, when the tilt of the Earth is either fully towards or away from the Sun.
I hope this puts the changing daylight hours you experience in a new light.
Enjoy!
Sunset over Mississauga, viewed from downtown Toronto
** atmospheric refraction can slightly impact the equality of the daytime/nighttime on the day of the equinoxes.
Acknowledgements:
Thank you to the python community, which has developed and maintained the packages I use to make nice plots, i.e. matplotlib, numpy, pandas, and calculate the sunrise/sunset, i.e. ephem, pytz.
