Arcturus in Broad Daylight
What
We observed the star Arcturus with unaided vision, hours before sunset on three occasions in 2020. This site will tell the story of the discovery, and explain a simple theory of what atmospheric conditions seem to allow for this rare observation. Any interested observer can try to duplicate our results. We hope to collect more observations.
When
July 6th, 7th, and 8th, 2020. Approximately 4:45 to 5:30 pm each day.
Where
Tucson, Arizona: The summer of 2020 in Southern Arizona was hotter and drier than normal. The humidity those days was extremely low, which most likely produced the conditions needed to see Arcturus.
Who
Jon Dokter, Jeanette Adrian, and Dr. Erin Galyen, all of Tucson, Arizona.
Jeanette Adrian was the first to notice the daytime star, laying on her back after a swim.
Jon Dokter surmised the object was Arcturus, and on the second day of observations confirmed it. Jon has a Master's degree in astronomy.
Dr. Galyen joined in the third day of observations to bring in another observer well-versed in astronomy. Erin also has a Master's in astronomy from SDSU, as well as a PhD in education from Arizona.
Why
We simply want to publicize the observation, and invite others to attempt verification. We hope follow-up observations will convince others it is indeed possible. Those who are passionate about stargazing will likely find it a tantalizing prospect, and we hope others will strive to see what we saw, perhaps by visiting Southern Arizona during a dry spell. We are asking for reports (email address below), and will post any that seem credible.
How
A few weeks after our observations, Jon researched Tucson humidity levels, and found that the humidity was exceptionally low on the days Arcturus was visible. Jon attempted to see Arcturus every clear day the rest of the summer, but it quickly became apparent that the sighting would not happen again during the relatively humid monsoon season. Jon theorizes that humidity below about 13% is required to make the atmosphere thin enough for a bright star observation in daylight. Extreme heat and a somewhat high elevation are probably also contributing factors (the observation happened in the Tucson foothills, around 2,500 feet above sea level).
* Jon intends to write in more detail on this theory and the observations. For now, see the link (below) to our initial write-up on the observations (August, 2020).
More...
What surprised me (Jon) the most was how easily visible Arcturus was. It reminded me of the appearance of Venus in a daytime sky. Once spotted, it seemed so obvious and "plain as day" (pardon the pun), it seemed impossible that this was not a well-known feature of the daytime sky! Since Venus is in fact much brighter than Arcturus, and I had previous experience seeing Venus in the daytime, this is what set me to thinking that unusual atmospheric conditions must have been at play. Something very strange had to be going on for Arcturus to be as easily spotted as Venus.
Most assume stars are seen at night only. This is true, for the most part. The planets Venus, Jupiter, and sometimes Mars, are actually visible in the daytime, but without dedication and practice, the typical person going about their day isn't going to spot a daytime planet. (Planets seen in the night sky have star-like appearance, and so Mercury, Venus, Mars, Jupiter, and Saturn are referred to as "stars" in the field of naked-eye astronomy.)
For that matter, the visibility of stars at night is itself a complicated issue in the modern world, due to light pollution from urban areas. A large fraction of humanity no longer experiences pristine night skies with thousands of stars visible at any given time on a clear night. In major cities, only a handful of the brightest stars (and planets) might be visible at night. This fact serves to make it perhaps extra hard to believe a star might actually be seen in the bright, blue sky.
Learning about the sky and which celestial objects are visible from a given location on Earth at a given time is truly a lifetime's pursuit. I've been watching the sky regularly since my teenage years, and I'm still in awe of the ever-changing sky, how much there is to see, and how it can still surprise me.
Those not practiced at stargazing and identifying specific stars/planets might not appreciate the rarity of this sighting. On the other hand, those who are very experienced might actually doubt our claim. The amount of writing it would take to explain every aspect of this issue (to people in either camp) would be excessive. Therefore, my goal with this web site is to keep it simple, and encourage interested parties to learn more about naked-eye astronomy from great sources, and to encourage all to try to duplicate our observation with their own eyes.
This is why astronomy is a great field, and why it was such fertile ground for Copernicus, Kepler, Galileo, and Newton to basically get the ball rolling on what would lead the world into the era of modern science. The sky is always there above all of us, waiting to be observed. If you have an idea about it, tell people, and let them see for themselves...
This site was launched April 24, 2021. Please return again soon to see how it evolves! For now, you can read my first attempt at publicizing this observation:
Click here to read the account I wrote in August, 2020.
Days after this site was launched, I was informed that the June, 2021 Sky & Telescope contained something on the daytime visibility of Arcturus. Kind of a coincidence, but there really wasn't much substance to it. It is perhaps an indicator of just how little has ever appeared in astronomy literature regarding Arcturus in the daytime. Click here for my take on it.
Bibliography
To become well-versed in the fundamentals of astronomy and observational basics, I recommend looking at the sky often (day and night), and reading...
Further observations
As the Southern Arizona air becomes hot and dry in the coming months, I will be attempting new observations and updating a blog about the effort.
Contact: Jon Dokter
Send inquiries to:
entropyratings@gmail.com