How to see stars, satellites and more in the daytime sky
Viewing celestial bodies during the day is possible, but not necessarily easy
It is clear that you cannot see the stars during the day.
But if you said that to me, I would gently take you by the hand, lead you outside, and silently point at the sun like an unrepentant, cocky person.
Jokes aside, our nearest star teeth The reason why you can’t see other stars during the day is part One reason is the atmosphere. Molecules in the air act like pinball bumpers, scattering sunlight photons in all directions. We are surrounded by these molecules, which is why we see sunlight hitting the sky from all directions. Earth’s air preferentially scatters blue photons, which is why the sky appears blue.
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and again brightThe stars are so dim that they’re drowned out by the scattered light — the contrast is so intense it’s like trying to hear a whisper at a heavy metal concert.
But scientifically speaking, being able to observe stars while the sun is up would be a huge boon for astronomers. Some stars undergo rapid changes as they begin to die. For example, in 2019 and 2020, the red supergiant Betelgeuse spewed so much dust that its visibility dropped by more than half, sending astronomers scrambling to figure out the physical processes behind the event. But for months at a time, Betelgeuse was virtually invisible, too close to the sun in the sky for glare to see, costing astronomers a lot of precious observing time. Many other celestial phenomena are similarly time-sensitive, which is why some astronomers have worked hard to find ways around the obstacle of Earth’s bright daytime sky.
Previous attempts to use professional hardware include a 1981 experiment in which an electronic device called a photometer (think of it as a very sophisticated light meter) was attached to a one-meter infrared telescope in Chile for successful daytime observations. Another experiment in 2007 attached a commercially available digital detector to a small refracting telescope and achieved very accurate photometric measurements, even for third magnitude stars (slightly fainter than the stars that make up the Big Dipper). In general, stellar brightness measurements can be made during the day to within about one percent accuracy, but of course this works best for brighter stars.
Recently, astronomers at Macquarie University in Australia were able to make such measurements using a test instrument called the Huntsman Telescope Pathfinder. Pathfinder combines a powerful but relatively inexpensive digital camera with a single off-the-shelf camera lens. It is a testbed for the entire Huntsman Telescope, which consists of 10 lenses working together to perform a deep, wide-angle survey of the sky. Of course, the instrument is typically used at night, but the astronomers wanted to verify its performance during the day.
Testing Pathfinder on 35 stars of different brightness and color during daytime hours when the sun was 30 degrees above the horizon, astronomers were able to achieve brightness measurement accuracy of 1 to 10 percent, a pretty good result considering the inherent difficulty of the observations. Exposure times must be very short so the bright sky doesn’t saturate the detector, and then thousands of images must be taken to gather enough signal from the target star to make it visible. Astronomers were able to detect a faint star of magnitude 4.6. wonderfulFor example, it is not much different from the brightness you can see with the naked eye in a dark place.
They also completed another impressive feat: detecting and tracking the International Space Station (ISS) as it moved through the daytime sky. The ISS is one of the brightest man-made objects in the sky, but it moves quickly and changes brightness dramatically. It is more than 1,000 kilometers from observers on the horizon, but only a few hundred kilometers overhead. Still, Pathfinder was able to resolve some of the ISS’s structural features, including its enormous solar panels and component modules, as it passed overhead.
These observations show that daytime observations of bright satellites and stars are possible with relatively simple instruments; more advanced instruments would undoubtedly produce better results. Such observations could be very useful in tracking the growing number of satellites in Earth orbit, a key aspect of space situational awareness.
But you don’t need a lot of equipment to see celestial objects during the day; you can see them with the naked eye. The Moon is the easiest to see because it’s the brightest object in the sky after the Sun. For example, if you’re close to a waxing quarter moon, you can spot it rising in the east before sunset. If you’re close to a waning quarter moon, you can also see it setting in the west in the morning, long after sunrise.
Venus is the third brightest object in the sky. (The ISS is even brighter, as are other moons, but we’re not counting them here because we made them.) When it’s the western “evening star”, Venus is incredibly bright – so bright that many people don’t believe it’s real and often mistake it for an airplane or UFO (or UAP).
Venus is bright enough to be seen even when the Sun is up. I’ve spotted it many times in broad daylight. The trick is to look for Venus when it’s near a celestial signpost: the much brighter and larger crescent Moon. Our natural satellite is much easier to see, and if you know where Venus is in relation to the crescent Moon, you can recognize the planet against its usually brilliant blue sky background. Planetarium software can help here, and many planetarium apps are available for free for mobile devices.
Comets can also be visible in the daytime. In 2007, Comet C/2006 P1 McNaught became so bright that it could be spotted in broad daylight. This is rare, but quite surprising when it does happen.
And there teeth Another way a star can become visible during the day is when it explodes. Supernovae are incredibly bright phenomena that could become extremely bright if they were to explode within our galaxy. For example, Betelgeuse could one day become as bright as the full moon when it explodes, but because it’s so far away, it would appear as a tear-jerking point of light in the sky that’s easily visible during the day. The only problem is that we’ll probably have to wait hundreds of thousands of years for Big B to explode. Hopefully, other Milky Way stars will go supernova themselves. Too close.
But astronomers are no longer limited to daytime eyes. Being able to observe the stars when the sun is up has a huge advantage. If there’s a downside, it’s that it means having to adjust your sleep schedule.
