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Australians are about to move into five different time zones as daylight saving begins in most states and territories across the nation, impacting millions of people. So what exactly is it?

"Australia has five different time zones during daylight saving. Astronomers avoid the issue all together by using Coordinated Universal Time (UTC), which stays the same all year round," said astrophysicist Laura Driessen from the听School of Physics.听 "It鈥檚 also the reason we have equinoxes, days where the sun crosses the equator and daytime and nighttime are almost the exact same length.鈥�

"Whether a state has daylight saving or not was decided based on practical reasons or by popular opinion, not because they get more or less sun than other states. Luckily, daylight-saving time doesn鈥檛 change how the Earth moves through the Universe.

"So, the length of the day is all about the Earth鈥檚 tilt, but how we choose to deal with it is decided by the state we鈥檙e in. Changing the clocks doesn鈥檛 change our orbit, just how we experience it."

"Pushing the clocks forward an hour results in a misalignment in our internal biological clock, otherwise known as our circadian rhythm," said Dr Nicholas Fuller, health and obesity expert from the and author of the new book, .听

鈥淭he one hour less sleep we get often has a flow on effect to our lifestyle choices the next day. Research shows that one night of sleep deprivation (less than seven hours of sleep) results in an increase in our hunger hormone, ghrelin. You wake up feeling hungrier and you鈥檙e more likely to make poor diet choices.鈥�

"Cows like routines and therefore any sudden change like milking an hour earlier or later will be noticeable in the yield of that day鈥檚 milking, but it will hardly affect total daily milk yield," said听Professor Yani Garcia, expert in dairy science and Director of the in the听School of Life and Environmental Sciences.听

鈥淢ilk secretion in the mammary gland is a continuous process, so as far as feed availability remains unchanged, any small effect due to daylight saving should become unnoticeable in just a few days.鈥�

鈥淏ut regardless of how we set the clock, there is a physiological and positive effect of photoperiod (or artificial light) on milk secretion. So, if all other conditions like feed and management remain the same, research has shown that cows exposed to longer daily photoperiod can produce up to 10 percent more milk.鈥�

鈥淭ransitioning to daylight saving means that we lose an hour of sleep on the night that 2am becomes 3am," said听, epidemiologist and research fellow in the听Charles Perkins Centre鈥檚 Sleep Group.

"There is research to show that across a whole population, there are adverse effects of this sleep loss, from more car accidents to more heart attacks and generally more grumpiness which affects those who work the next day and their productivity.

鈥淚nternationally, there have been campaigns by sleep and circadian scientists for governments to get rid of daylight saving and instead adopt a permanent time that is in line with circadian rhythms. However, we have not had that conversation yet in NSW. Is daylight saving perhaps unnecessary given that daylight hours are longer in summer anyway? It鈥檚 also unclear if shifting the use of electricity from the evening to the morning saves on energy 鈥� a key reason that daylight saving was first introduced.鈥�

鈥淗umans were designed to sleep at night when it鈥檚 dark and to be active and alert when the sun is out. With daylight saving, clocks move forward, giving us longer evening light but darker mornings. That shift disrupts circadian rhythms and can lead to misalignment of our body clock with natural light-dark cycles. For example, more light in the evening can delay sleep and morning darkness can affect exercise and alertness," said听Dr Emiliana Tonini, a postdoctoral research associate in sleep and mental health at the听Brain and Mind Centre.

鈥淐ircadian disruption is associated with a lot of different health problems, such as cardiovascular disease, metabolic presentations, and mental health conditions. The potential negative impact of daylight saving must be considered carefully, especially in populations that are already more susceptible to circadian disruption, such as teenagers or shift workers.鈥�

"Companion animals may be impacted by daylight saving, in that they don't receive advanced warning that clocks will be wound forward, nor do they appreciate why their routine (or ours) might change," said听, clinical vet and lecturer in the Sydney School of Veterinary Science.听

"Whether people use more or less energy during daylight saving is still contested,"听said Dr Glenn Platt, Professor of Practice in the听School of Electrical and Computer Engineering听and Director at Emergent Group.

"In 2024, the availability of technologies such as home solar and home batteries, and electricity tariffs where the peak price occurs late in the afternoon to early evening complicates things even further: it is hard to work out how exactly energy consumption has shifted due to the time of day changing, or whether it is due to energy tariff or technology changes."

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