September 2024 Stargazing Guide

Greetings junior scientists, scientists and citizens is this great big weird wild and wonderful world in which we live. As always I'm your humble science communicator the great Orbax coming to you from the Department of Physics here at the University of Guelph and I'd like to welcome you to our September 2024 Star Gazing Guide!

It's September and that means a return to school for many of you junior scientists out there and while September days are filled with studies September nights are full of wonder. This month Saturn has its brightest night of the year, we scan the skies for an exploding star, witness a partial lunar eclipse and welcome in the first day of Autumn with the Equinox. All this and more if you just take some... time to look up.

The summer triangle has been with us, well... all summer and I want you to take one last look at it. Earlier this summer the triangle would rise in the East but now it appears almost directly overhead at Sunset. Find the upper vertex in the brightest star of the triangle, Vega, in the constellation Lyra the Lyre. Now I want you to look due West and find one of the other brightest stars in the sky, Arcturus appearing in the constellation of Bootes the Herdsman. If we draw a straight line between these two stars you will spot two constellations. Hercules, and the one we're interested in this month, Coronae Borealis the Northern Crown. Coronae Borealis contains a special star T Coronae Borealis or T CrB. T CrB is a binary star system comprised of a red giant and a white dwarf which is about to explode. The white dwarf is a star about the size of Earth with a mass equal to our Sun's. This super dense star is drawing hydrogen from the red giant. The hydrogen accumulates on the white dwarf and the buildup of pressure and heat eventually triggers an explosion called a Nova causing a huge burst of light and energy and eventually returning the star to its original luminance where the whole cycle begins again. This Nova occurs about every 80 years and astronomers believe that we might be able to see it this month. When the Nova occurs the burst of light should be visible in the night sky for at least a week. Good luck junior scientists!

As we enter into the Autumn months our gas giants Jupiter and Saturn return to our night guys with Saturn visible in the Southeast at Sunset and Jupiter rising closer to midnight at the beginning of the month. As a matter of fact Saturn's actually in opposition on September the 8th... which is just a fancy term for when the Earth lies directly between the Sun and Saturn. This means that Saturn will be at its brightest, fully illuminated by the Sun and in the sky all night long. With a telescope and potentially even just binoculars you should be able to see the rings of Saturn. Good luck junior scientists!

The full Moon this month occurs on September 17th and is yet another Super Moon. We've talked about Super Moons in the past. These occur when the Moon is slightly closer to the Earth in its elliptical orbit, a point known as perigee. Here it's 40,000 km closer to us than at its furthest point, apogee, and therefore appears to be 30% brighter and 14% bigger. It's also our second of four consecutive Super Moons this year.

Now during this month's Full Moon we're also going to experience a partial lunar eclipse. A lunar eclipse occurs when the orbits of the Sun, the Moon and the Earth line up in such a way that the Earth's shadow is cast onto the Moon. The Earth casts two shadows in this situation. The darkest one is the Umbra and when the moon Falls entirely into this Shadow we get what's called a total lunar eclipse. The second Shadow is known as a Penumbra and is a lighter shadow that on a full Super Moon like this one might go entirely unnoticed. Now when I say this is a partial lunar eclipse I mean it's REALLY partial. Only 3.5% of the Full Moon will be covered by the Umbra but if you happen to be awake at 10:44 p.m. on the night of the 17th take a look at the Moon and see if you can see a tiny chunk taken out of the side of the Super Moon! Unlike solar eclipses, lunar eclipses are totally safe to observe with the unaided eye.

This month's full moon is the closest one to the Autumnal Equinox and is typically referred to by settlers as the Harvest Moon. The Mi'kmaw refer to the September Moon as the Mate Calling Moon, Wikumkewiku's, as do the Cree Nation of central Canada who refer to it as Nimitahamowipisim, the “Rutting Moon” - when the bull moose scrapes the velvet from his antlers as a sign that mating shall begin.

Now, as I mentioned earlier, September 22nd is the first day of autumn and here's why.

We all remember the Earth is tilted at 23.5° with respect to the line perpendicular to the plane of our orbit around the Sun. One Earth year corresponds to one full solar orbit. In December we talked about the winter solstice and in June we talked about the summer solstice. The solstice occurs on a day when we are either closest to, or furthest away from, the Sun due to that tilt. These are the days when we experience the most daylight hours or the least daylight hours, the two extremes. Now exactly halfway between the solstices we experience a day with equal amounts of daylight and nighttime hours. This is known as The Equinox. The Autumnal Equinox occurs on September 22nd and denotes the first day of Autumn. After this point our daylight hours will decrease until we reach the winter solstice. This phenomena occurs again in 6 months from now once we've passed 180° through our orbit around the sun in the springtime for the Vernal Equinox.

What a month! So many things to see in our sky and consider this, what we're able to observe is only the tiniest fraction of all the things that are actually occurring in this incredible Universe that we find ourselves part of. It's all out there just waiting for you to take some time... and look up.

See you next month junior scientists and don't forget to have a science-tastic day!

Special thanks to Royal City Science's own planetary geochemist Dr Glynis Perrett for her help preparing our Star Gazing Guide.

And the Royal Astronomical Society of Canada.