Daylight saving time – love it or hate it

Because of daylight saving time, you'll have to stay up an hour later to see Saturn in the east. Created with Stellarium

Daylight saving time. I don’t whether to love it or hate it. We lose an hour of early morning daylight but gain an hour in the evening. After nearly five months of winter, more light at the dinner hour is most welcome.

On the other hand, a later sunset means a later start to the night. Yesterday, twilight ended and true night began a little before 8 p.m. Tonight that becomes 9.  Saturn rose at 8 p.m. last night and will do so at 9 p.m. tonight. Since we’ll have to wait an additional hour for stars to come up in the east, daylight saving time has the effect of retarding every star’s rising by an hour.

Wait a minute. I was just getting used to seeing Saturn and the stars of early spring up in the east long before the 10 o’clock news. Does that mean we’re stuck with winter stars for a while longer? Yes. That’s the part of daylight time I don’t like. That and the hour of sleep I have to wait 7 months to get back.

As always, patience is necessary in astronomical pursuits. Soon enough, Earth’s journey around the sun will compensate for the later rising time. In only two weeks, Saturn and friends will be up where they used to be at 9 o’clock.

It works like this. Every night, the stars rise four minutes earlier than the night before. Over the days and weeks, the minutes accumulate into hours. When stars rise earlier, that means they also set earlier, causing them to drift westward over time.

View of Earth's orbit around the sun seen from above the northern hemisphere. As our planet moves to the left, the background constellations appear to drift to the right or westward. Credit: Bob King

The spring constellations are now low in the eastern sky, but in two months they’ll all be high in the south. As Earth travels in its orbit around the sun, we peer out into different sectors of the sky at night as the weeks and months pass. Think of sitting on one of those merry-go-round horses and looking out into the carnival crowd. As the merry-go-round turns, we look out at a different part of the fairground during our little spin. Now substitute the Earth for the horse and our orbit for the merry-go-round.

This time exposure shows stars trailing across the sky from east to west (left to right). This nightly motion due to Earth's rotation is different from the slow drift caused by Earth's revolution around the sun. Photo: Bob King

During Earth’s “little spin” around the sun, we see the stars and constellations drift from east to west across the sky as we pass them by.

This isn’t the same as the nightly rising and setting of stars – that’s due to Earth’s rotation. Every star you see makes a complete circle around the sky in 24 hours. The much more leisurely seasonal drift is superimposed on that pattern. It reveals itself to sky watchers who spend time regularly under the stars.

One thought on “Daylight saving time – love it or hate it

  1. As we used to discuss Bob, we (in Australia) are slapped with Daylight Saving for just over 6 months every single year & personally, I hate it. Of our 8 States & 2 Territories, some have DLS, some don’t, some start earlier, others later – a mad house). We are into our 3rd week of Autumn in Australia now and we still have to wait until 2100 local for Astro-Sunset with DLS. The “Dog Star” is our first Cab off the Rank here in Adelaide and near enough, directly overhead & can be seen from around 2020 (approx) on clear nights. I have personally noticed a change in our Weather Patterns in Adelaide over the past 30 plus years. We are getting a HUMID AIRFLOW from the North West of Australia as a matter of course now. Previously, it used to contine directly across the TROPIC OF CAPRICORN in an Easterly Direction, now it sweeps South & East over Australia and so this year (in particular) the number of nights suitable for viewing would be a mere couple of dozen (conservatively). I hate Daylight Saving with an absolute vengeance but obviously, Star Gazers are a minority in the Population, sadly. Clear Skies & regards, Noel.

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