Winter Solstice this weekend

Sunday, June 21, at 6:25 pm Sydney time

This weekend marks the Winter Solstice in Australia and is also the longest night of the year and the shortest day.

Why do we have longer nights in winter?

The reason for the seasons and the changes in the length of the days and nights is because the Earth orbits the Sun at a slight tilt of about 23 degrees. 

During the southern hemisphere winter months, our parts of the world are pointed away from the Sun. The Sun will appear in the part of the sky north of the "ecliptic" which is the line drawn around the middle of the sky.  The Solstice marks the date when the Sun is as far north as it's going to get. From now on, it will move south until the Summer Solstice in December when (as you might have guessed) it reaches it furthest southern point and starts the journey north again.

The Earth during the southern winter solstice

While we see the Sun move from east to west during the course of the day, the actual part of the sky where it's located changes constantly. 

These longer nights are a delight for astronomers and with the rich central core of our home galaxy during the winter months, "Milky Way Season" is an ideal time for wide field astrophotography. 

If this is the shortest night, is it the coldest day of the year?

No.

The reason is the atmosphere, land and oceans retain a lot of heat from the warmer summer months. It takes them a while to cool down. The coldest month in Australia is usually July.

It's not the start of winter, at least not in Australia

Many parts of the world including much of the north hemisphere, mark their season changes with the solstices and equinoxes. In Australia we start winter on the first of June. The dates of the solstices changes by a couple of days from year and using the calendar method allow better record keeping for farming and graziers. 

What if the Earth didn't have a tilt, would we still have seasons? What about the rest of the Solar System planets?

No. 

The reason why we have seasons are entirely due to our planet's tilt. 

Other planets including Mars, Saturn and Neptune have tilts not too far away from Earth and they all experience seasons as well.  Jupiter and Venus only have a miniscule tilt and don't have seasons. (Some would suggest that Venus has close to a 180 degree "tilt" as it spins backwards compared to other planets and is in fact upside down!)

Neptune's tilt is almost 98 degrees, and it effectively spins on its side, making its seasons decades long.

Nancy Grace Roman Telescope countdown

As large as Hubble, with a field of view 100 times wider, due to launch on the 30th of August 2026 on a SpaceX Falcon Heavy

The latest space telescope from NASA has a unique mission. Over the next five years, it's going to be tasked with surveying and capturing large chunks of the night sky in unprecedented detail. Hubble and more recently the Webb Space Telescope have enchanted us all with close up details of both the deep-sky and Solar System. Roman will continue these types of observations, while covering much larger regions of the sky.  

It's named after NASA's first chief astronomer, Nancy Grace Roman, who's often been called the "mother of the Hubble Space Telescope".

A NASA illustration of the Nancy Grace Roman Space Telescope

It has the roughly the same size optics the famous Hubble Space Telescope but with a vastly wider field of view. Astronomers hope it reveal more about dark matter and dark energy as well as expanding the number known exoplanets and getting a better understanding of the star systems where they've formed. 

Whenever new, large cutting edge telescopes and observatories start exploring the Universe, it's the unexpected discoveries that are often the most exciting. We're all looking forward to what the Roman Space Telescope will reveal. 

What's also amazing about this telescope is that it's being launched under budget and ahead of schedule.  NASA Administrator Jared Isaacman said recently:

"The Nancy Grace Roman Space Telescope is in final preparation for launch, eight months AHEAD of schedule and UNDER budget. 

This milestone is the result of more than a decade of dedication and millions of hours of work by NASA and our industry partners. Their commitment is what’s making this moment possible and helping drive Gold Standard Science. 

Roman will help answer some of the biggest questions in science, investigating dark matter, dark energy, and the structure of the universe. Its images will be so large and detailed, there isn’t a screen in existence big enough to display them."

Hitch a ride with Roman!

Until the 12th of July 2026, if you visit this NASA site you'll be able to add your name to a special SD memory card that will fly with the Nancy Grace Roman Space Telescope and even score your own NASA boarding pass:

You can part be of the mission and be connected with this very special astronomy project. 

Cheers,

Earl White

BINTEL

20th June 2026