Daylight Saving Time Pros and Cons for Skywatchers

I'm no fan of Daylight Saving Time. In spring it means we all have to stay up an hour later until the sky gets dark. That's OK...

Planets fea

Planets March 12
You can "step" from the crescent moon to one bright planet after another tomorrow morning at dawn the same way you might cross a creek on the biggest, steadiest rocks. The ecliptic is the plane of the solar system seen from Earth, and the path the planets, sun and moon take across the sky. Stellarium

I'm no fan of Daylight Saving Time . In spring it means we all have to stay up an hour later until the sky gets dark. That's OK for now but by summer, when the sun sets at 9 o'clock followed by more than 2 hours of twilight, I've had my fill. Still, that extra hour of darkness we now have in the morning is sweet because it makes dawn sights more accessible.

With the sun now rising around 7:30 a.m., the same time it did without DST in the first week of February, it's easier for 9-5 working stiffs like myself to see celestial happenings at dawn that it was just one day ago. Fortunately, we can illustrate this time bonus with a scenic moon-planet gathering that occurs tomorrow morning March 12.

Instead of setting your alarm for 5:30 a.m. to see the hour-before-sunrise sky tomorrow, you can now sleep in an hour and get up at 6:30 a.m. When you do, face south and find the crescent moon off to the southeast. A fist and a half to its right and above is the planet Saturn. A fist to the right of Saturn, you'll alight on ruddy Mars. Three fists to the right of Mars stands the current brightest morning sky planet, Jupiter.


The map above shows the constellations that currently house these solar system pals. An hour before sunrise you may only notice Antares, a first magnitude star in Scorpius, but if you're out around 6 a.m. (90 minutes before sunrise) at the break of dawn, you'll see the full constellations in a darker sky.

Daylight saving time old 1918 poster
1918 post card that citizens could mail to their congressman to show support for the daylight saving time law, which was enacted on March 19, 1918 in the U.S. Click to read the history of DST. Credit: Library of Congress

The benefits of the extra pre-dawn hour won't last for long. The sun continues to rise earlier and earlier, chipping away at our bonus minutes until the June solstice, when it brightens the curtains around 5:30 a.m. Here again, DST comes to the rescue. Were it not for "spring forward an hour," the sun would rise at the unnatural stroke of 4:30 a.m. on the solstice.

Sirius Daylight saving time panel
Sirius, the brightest star, heads up the constellation Canis Major the Big Dog and is very prominent in the southern sky this month. With the start of daylight saving time, it now appears one hour east (to the left) of where it was last night at the same clock time. Stellarium

Daylight time also retards the departure of the winter constellations from the sky in March (and the spring constellations' appearance in the east) and hastens the winter groups' arrival in the east in November (and the departure of the fall groups), when we "fall back" an hour. Consider. If you looked up last night, twinkly, bright Sirius stood to the west  (right) of south around 8:30 p.m. and set around 12:30 a.m. Tonight, with DST in effect, Sirius stands to the east (left) of south at the exact same clock time and sets around 1:30 a.m. — a delay of one full hour. Likewise, the spring constellations in the east lag by an hour.

The reverse happens in November when DST boots Orion and Sirius into the evening sky an hour earlier. If you like seeing Orion, DST's your friend, but if spring's on your mind, it's not.


Confound it all. The more I write about Daylight Saving Time, the more equivocal I become. We'll call it a draw. When it comes to astronomy, the time change takes the edge off morning observing but makes the evenings sleep-killers. What do you think?

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