It’s almost time to get your coats out, pour yourself a large pumpkin spice latte, and start picking your conkers.
That’s because autumn officially begins tonight!
The autumn equinox takes place at 19:20 BST Monday – marking the point when the sun appears to shine directly over the equator.
This annual astronomical milestone officially heralds the arrival of autumn along with gradually colder temperatures for the Northern Hemisphere.
And it means daytime and nighttime are nearly equal lengths all around the world.
After tonight, as we get further into autumn, daytime will gradually keep getting shorter until the arrival of winter.
‘In the Northern hemisphere, the September equinox marks the start of a period bringing us later sunrises and earlier sunsets,’ NASA explains.
‘We will also feel cooler days with chillier winds, and dry, falling leaves.’
It’s almost time to get your coats out, pour yourself a large pumpkin spice and start picking your conkers . That’s because autumn officially begins tonight
It’s well known that Earth is tilted on its axis, which is why we have seasons.
As our planet orbits the sun, the sun illuminates either the northern or southern hemisphere more, depending on where the Earth is along its orbit.
However, at two points in the year the sun will illuminate the northern and southern hemispheres equally.
These are known as the equinoxes, and in the Northern Hemisphere they happen in March (the official start of spring) and September (the official start of autumn).
Anna Ross, an astronomer at the Royal Observatory Greenwich, explains: ‘Earth takes one year (or 365–and–a–quarter days) to orbit once around the sun and it is tilted over slightly on its axis.
‘So for half of the year, the Northern Hemisphere is tilted slightly towards the sun, meaning we have longer daylight hours and hotter temperatures.
‘For the other half of the year, we are tilted slightly further away from the sun so we have longer nights and colder weather. It’s this tilt that gives us our seasons.
‘There are two points in the year where the Earth’s tilt is at its most extreme relative to the sun.’
NASA graphic explains the difference between the solstice and the equinox. The solstices take place in June and December; the equinoxes take place in March and September
Occurring twice per year, equinox is when the sun crosses the plane of the earth’s equator, and day and night are of equal length. Pictured, spring equinox in 2024
Of course, when the Northern Hemisphere enters autumn, the Southern Hemisphere enters the other equinox (spring).
So in Australia for example, temperatures will now start to get warmer and flowers will start to blossom.
For the Northern Hemisphere, tonight’s equinox kicks of the countdown to the winter solstice – the shortest day of the year and the start of winter – on December 21.
Solstices – which are essentially the opposite of the equinoxes – occur when the planet’s geographical pole in the Northern or Southern Hemisphere is most greatly inclined towards the Sun.
‘There are two points in the year where the Earth’s tilt is at its most extreme relative to the sun,’ said Ross.
‘These days are known as the solstices.
‘On these dates, depending on which hemisphere you live in, you will either experience midsummer with the longest day of the year or midwinter with the longest night.
‘In between both of these extremes, we get our spring and autumn months, with the exact midpoints being the equinoxes.’
If you think that autumn already started on September 1, a meteorologist would agree with you, although an astronomer probably wouldn’t.
The astronomical definition of when seasons start and end are based on the Earth’s tilted orbit in relation to the sun.
But meteorologists use another definition – where the Northern Hemisphere’s spring, summer, autumn and winter always begin on the first day of March, June, September and December, respectively.
This alternative definition, rigidly defined by the months of the year, makes it easier for meteorologists and climatologists to compare seasonal and monthly statistics.
The Met Office explains: ‘These seasons are split to coincide with our Gregorian calendar, making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics.’
The ‘astronomical’ definition is more readily accepted, however, because it has more of a physical, scientific basis.
This article was originally published by a www.dailymail.co.uk . Read the Original article here. .