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.
Sirius Setting at
Altitude of Sirius at Sunset
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.
Cosmonaut Yuri Gagarin became the first human in space on board Vostok 1 on the morning of April 12, 1961.
The event is celebrated as Yuri’s Night around the world each April. The 2020 celebration is a virtual World Space Party at https://party.yurisnight.net/ 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.
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 space.com has more on how the first human spaceflight worked.
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:
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
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.
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.
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.
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.
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.
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.
Two Canadian women astronomers are featured prominently at the Hogg Memorial Lecture that is part of the RASC 2020 General Assembly in Vancouver. The Hogg Lecture is named in recognition of the lifelong contributions of Dr. Helen Sawyer Hogg towards increasing public awareness and appreciation of the Universe. It is held annually alternating between the RASC General Assembly in even-numbered years and CASCA’s conference in odd-numbered years. Dr. Sara Seager is delivering this year’s Hogg Lecture during the RASC 2020 GA on June 6th, 7:00 pm at Simon Fraser University. The lecture is free and open to the public – register now.
Dr. Helen Sawyer Hogg
Dr. Hogg was a notable woman of science in a time when many universities would not grant scientific degrees to women. As an astronomer, she is recognized for pioneering research into globular clusters and variable stars.
Hogg did graduate work at the Harvard Observatory where she worked with Dr. Harlow Shapley measuring the size and brightness of globular clusters and publishing several papers. Hogg received her master’s and doctoral degrees from Radcliffe College because, at that time, Harvard refused to award graduate degrees in science to women.
In 1931, she and her husband Frank set out in their Model A Ford for Victoria BC and the Dominion Astrophysical Observatory where a position awaited Frank. There was no opening at the DAO for Helen, but the Director gave her the use of the 72-inch telescope to further her research. The couple moved to Toronto’s “new” Dunlop Observatory in 1935 where Hogg continued her study of variable stars in globular clusters.
Her successful professional career was matched by her generous community activities, many of them reflecting her efforts to ensure that
“The Stars Belong to Everyone”
Helen Sawyer Hogg
which is the title of one of her popular books and adopted as the theme of the 2020 GA. She prepared a weekly astronomy column for The Toronto Star for 30 years, starred in an astronomy TV show, and wrote numerous articles for the Journal of the RASC. She was the first woman president of the physical sciences section of the Royal Society of Canada, as well as the first female president of the Royal Canadian Institute, and a national RASC president.
Dr. Hogg was promoted to a Companion of the Order of Canada in 1976 and posthumously inducted into the Canadian Science and Engineering Hall of Fame. RASC included her among 15 eminent astronomers that were named as Honorary RASC Members.
Dr. Sara Seager
The Hogg lecture at the 2020 General Assembly will be given by Dr. Sara Seager. She is a planetary scientist and astrophysicist at the Massachusetts Institute of Technology. Dr. Seager has pioneered research in the field of exoplanet atmospheres and now, like an astronomical Indiana Jones, is on a quest seeking the field’s holy grail, another Earth-like planet, searching for life by way of exoplanet atmospheric biosignature gases.
Seager’s research has introduced many new ideas to the field of exoplanet characterization, including work that led to the first detection of an exoplanet atmosphere. She was part of a team that co-discovered the first detection of light emitted from an exoplanet and the first spectrum of an exoplanet.
Seager’s research now focuses on theoretical models of atmospheres and interiors of all kinds of exoplanets as well as novel space science missions.
Her Hogg lecture on Mapping the Nearest Stars for Habitable Worlds is free and open to the public.
She is the author of two textbooks and has been recognized for her research by Popular Science, Discover Magazine, Nature, and TIME Magazine. Seager was awarded a MacArthur Fellowship in 2013.
Professor Sara Seager was born and grew up in Toronto, Canada. Among her first memories is a trip to a “star party” with her father, to see the moon through a telescope—spectacular! Professor Seager graduated from Jarvis Collegiate Institute, a 200-year old public high school known for its science education. During high school she was astounded to learn that one could be an astrophysicist for a living, only to be deterred by her father, who believed the best career was as a doctor or lawyer.
Seager graduated with a BSc in the Math and Physics Specialist Program at the University of Toronto. Like Hogg, she did graduate work at Harvard where her realization of the surprising diversity of exoplanets has led to Seager’s maxim, “For exoplanets, anything is possible under the laws of physics and chemistry.”
Today, February 29th 2020, is a leap day with an extra 24 hours added to the calendar. The extra day is added to keep our calendar aligned with the seasons. The need for a Leap Day is a result of the physics with the Earth rotating on its axis while simultaneously revolving around the Sun. Physics also explains why the need for leap years will eventually disappear!
Our calendar year is designed to match the seasons, which occur because of the axial tilt of the Earth. At the June solstice, the northern hemisphere is tilted towards the sun but it is tilted away from the Sun at the December solstice. Neither hemisphere is tilted towards or away from the Sun at the equinoxes.
But the Earth is also simultaneously spinning on its own axis, with a period of 24 hours that make up our cycle of days and nights. The 24-hour solar day is the time it takes between successive “noons” – the time when the Sun reaches its highest point in the sky as seen from Earth. The solar day is about 4 minutes longer than the time the Earth to rotate by 360 degrees (called the sidereal day) because the Earth is moving around Sun during each day.
The calendar was originally intended to start at the Spring Equinox with a calendar year measuring the time it takes for the Earth to revolve around the Sun and make it to the next Spring Equinox.
The calendar year is the period of our orbit around the Sun but it does not match up with the whole number of 365 solar days – it takes a bit of an extra day for the Earth to get back to the same position with respect to the Sun.
The calendar year is 365.24219 solar days.
The extra 0.24219 days is close to 0.25 or ¼ of a day so adding an extra day every 4 years keeps the seasons and the calendar synchronized. It is a bit more complicated because the extra 0.24219 is not exactly ¼ and the Gregorian Calendar accounts for this with its leap year rule:
A year is a leap year if it is evenly divisible by four, but years that are divisible by 100 are not leap years, unless they are also divisible by 400.
For example, 2020 is a leap year, the years 1700, 1800, and 1900 are not leap years, but the years 1600 and 2000 are.
In the long term, changes in the Earth’s rotation rate need to be taken into account. The Earth’s rotation rate is slowing down, mostly due to the tidal forces and friction between the Earth and Moon. The day gets about 1.4 milliseconds, or 1.4 thousandths of a second, longer roughly every 100 years. A leap second is occasionally applied to accommodate for this slowdown in the Earth’s rotation and other irregularities. If you can wait around for about another four million years then the day will have lengthen by about 56 seconds. That is enough so that a calendar year will have exactly 365 solar days and we won’t need a leap year!
So enjoy the leap day while you can and a Happy Birthday any leaplings born on Feb 29th.
Betelgeuse is a bright star in the shoulder or armpit of the constellation Orion. It is easily visible in February and March from Vancouver around 10 pm, close to the southern Horizon.
If you follow astronomy news at all you’ll have heard that Betelgeuse has recently been dimming. Betelgeuse is a variable star whose brightness is known to periodically rise and fall, but it’s recent dimming has been quite extraordinary. Especially exciting is speculation that Betelgeuse may explode as a brilliant supernova which would be visible even in daylight. Unfortunately the latest measurements have shown that Betelgeuse may be brightening again,
Less often reported is that Betelgeuse is BIG! – not too surprising given that it is classified as a red supergiant. So how big is it?
It is so big that its diameter is about 1300 times that of our sun.
It is so big that if placed at our Sun’s location, the outer edge of its photosphere would reach out to Jupiter.
It is so big that it was the first star to have its angular diameter measured. Stars are so far away that they appear as pinpoints of light whose angular diameter cannot be determined. But Betelgeuse was big enough that 100 years ago, in 1920, it was the prime candidate to submit to measurement of its angular diameter.
Michelson and Pease used the 2.5 m Hooker telescope at the Mount Wilson Observatory in California – the largest telescope in the world between 1917 and 1949 – but even it was not large enough to resolve the disk of Betelgeuse. Instead Michelson turned the telescope into an interferometer by attaching a framework with 4 six inch mirrors to the front of the telescope.
The mirrors created 4 separate light paths of the star that combined, due to the wave nature of light, into an interference pattern.
Astronomical interferometers can produce higher resolution astronomical images than any other type of telescope – theoretically producing images with the angular resolution of a huge telescope with an aperture equal to the separation between the light paths. The separation between the mirrors of Michelson and Pease’s interferometer at Mount Wilson was about 20 feet (or 6 m) and this proved sufficient for them to measure the angular diameter of Betelgeuse as 0.047 arc-seconds.
Once you know the angular diameter, then if you also know the distance of the star, you can easily get its linear diameter in space. Michelson and Pease used several estimates of the distance to Betelgeuse available in 1920 to come up with a linear diameter of 386,000,000 km, somewhat smaller than more modern estimates. Using their 0.047 arc-seconds angular diameter with current estimates of the distance to Betelgeuse (about 724 light years) gives a linear diameter of 1.83 billion km — a truly colossal diameter, the equivalent of over 1,300 solar diameters!
Michelson and Pease published their results in the May 1921 edition of the Astrophysical Journal but a summary “Betelgeuse: How its Diameter was measured” appeared one month earlier in the April 1921 edition of the RASC Journal.
Betelgeuse is a peculiar star that is subjected to pulsation cycles that not only make is brightness vary but also make its size vary. Long-term monitoring by UC Berkeley’s Infrared Spatial Interferometer (ISI) on the top of Mt. Wilson show that Betelgeuse shrunk in diameter by more than 15% from 1993 to 2009. Recent images show that Betelgeuse has an asymmetric surface and appears to be shedding gas and dust at tremendous rates.
Since Betelgeuse has a radius 1,300 times that of the Sun, it has a volume about 1.3 billion times larger than the Sun. But its mass is only about 8 – 20 times the Sun. This means the density of Betelgeuse is much, much lower than the Sun. The average density of the Sun is about 1.4 grams/cc – somewhat higher than the density of water. In contrast, the average density of Betelgeuse is just 12 billionths of a gram/cc. This is about a million times less dense than Earth’s atmosphere at sea level, or about the same as a vacuum found in an insulating Thermos bottle.