How can I do astronomy during the day?
Just because the nights are getting short doesn’t mean you can’t stargaze. We take a look at all the different kinds of astronomy you can do while the Sun is still up in the sky.
Astronomy doesn't need to stop just because the Sun's come up. Here we list out some of our best tips to take advantage of the good weather during do some astronomy during the day.
From observing the Sun, to stargazing during the day, we look at the best ways to double your astro-fun and do some daytime stargazing.
How to observe the Sun
The most obvious candidate is naturally our own star, the Sun. Extreme care has to be taken however, as it can damage your eyes, even naked-eye viewing without any form of filtering is dangerous – looking through optics can cause permanent damage.
One of the most spectacular solar observations is a solar eclipse, where the Moon passes in front of the Sun and block its light out for a short while.
Eclipses can last a few seconds to up to eight minutes, the difference in duration of solar eclipses comes down to the fact the Moon’s orbit is slightly eccentric. Sometimes the Moon is closer to the Earth making totality last longer.
Then when the Moon is at the other extreme at its furthest from us it doesn’t quite cover the solar disc, and so we see a ring of fire, such as will be seen in India and the Middle East this June.
But therein lies the problem – to see an eclipse you usually have to travel, often to far-flung, sometimes quite remote locations.
So, as our world reels from the effects of the coronavirus pandemic, for the time being many of us will have to be content with remote observations streamed from observatories lucky enough to be on the eclipse shadow centre line.
That isn’t to say the Sun isn’t worth looking at (with proper safety precautions) when it’s not being eclipsed.
White light observing allows you to safely view sunspots and surface granulation, along with bright patches known as faculae near the limb of the Sun where the disk is slightly darker.
For more on this, read our guide on how to observe sunspots.
Specialist Hydrogen-Alpha telescopes and eyepieces bring out a view of the red chromosphere, with spectacular prominences and loops on the disc's edge that in the past were only visible during an eclipse.
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It’s also possible to see prominences on the Sun’s main disc, where they are called filaments and stand out as dark curvy lines on the surface of the Sun.
How do I observe the Sun safely?
Looking directly at the solar disc is dangerous and can potentially permanently damage your eyesight. You should never look at the Sun directly through an unfiltered telescope or binoculars. Fortunately, there are many methods to look at the Sun safely.
- Project the view through a telescope or binoculars onto a piece of card. Remember to cap off any optical finder to ensure no one looks through it accidentally.
- Buy a Hershel Wedge Prism which replaces your diagonal in a refractor and transmits a much reduced, safe amount of light to the eyepiece or camera.
- Use a white light solar filter. You can buy the film and make a filter yourself or buy a premade one. Just make sure it fits snuggly so it won’t fall off when you are looking through the telescope.
- Specialist solar telescopes and eyepieces are expensive, but can give some spectacular views of the Sun at different wavelengths.
Observing the Moon during the day
The Sun is the obvious daytime target, but it is surprising to many that the Moon is also viewable during daytime depending on its phase.
As it moves away from the proximity to the Sun it is initially difficult to see but during the few days either side of the First Quarter it becomes easily noticeable in the afternoons well before sunset.
Although somewhat washed out by the blue sky it is nonetheless fascinating to use the naked eye to spot the dark ‘seas’ amidst the bright highland terrain.
If you are an early bird and enjoy the mornings then the days either side of Last Quarter offer a good chance to see the Moon.
Telescopes will bring out some of the features usually viewed at night but again they will be more washed out due to the brightness and blue cast of the daytime sky but detail along the terminator will be viewable.
Looking at the planets
Because it can be reasonably obvious to spot the Moon with the naked eye it can help us find some of the brighter planets too.
Based on what we’ve already noted, in most cases it follows that it is only when the conjunction between the Moon and a planet occurs that it can guide you to spot Venus, Jupiter, Mercury, Mars (at its brightest) and Saturn.
On other occasions we have spotted Venus and Jupiter without the help of the Moon, but when they were highest in the south with the Sun at least 60 degrees away from them.
The sky this far from the Sun is darker giving better contrast for spotting the two brightest planets in daytime.
This is also where apps and planetarium programmes can give a good idea of where to look for them, especially if they have a compass option so you can hold the phone up to the sky then look in that direction or aim your binoculars or telescope.
Telescopically, Venus is the brightest and easiest to locate. Jupiter and Saturn look like pale, imitations of themselves. Mars is best when it is at its biggest and brightest but still appears ghostly.
Mercury should be as far from the Sun as it can get for you to spot it with a telescope.
Use filters to help pull out a little detail, especially with Venus – an ultraviolet filter will tease out subtle markings while a red filter darkens the background sky.
Seeing stars during the day
The same applies to stars. Wait, what, stars? Yes you can see them, although you will need a telescope. Using the same techniques as for the planets it is possible to view a few of the brightest stars during daytime, making for a fun and unusual project.
The key is to have them in the south with the Sun over in the western sky, which for our viewing was a couple of hours before sunset.
We used our 80mm ED refractor to view the primary stars of Orion including Betelgeuse, Rigel, Bellatrix and Alnitak along with Iota Orionis, although its binary companion was not viewable. We also tracked down Capella, Procyon and Aldebaran.
For stars lower down in the sky, there’s more haze to spoil the view, but we did spot Sirius with 10x50 binoculars over in the south, half hour before sunset.
With our telescope we estimated that the cut-off limit was mag 3 but it does depend upon sky conditions and how high they are in the sky.
What atmospherical space effects can I see during the day?
Another great thing to see is a mixture of astronomical and atmospheric effects. When there is a fine, high-level haze or cirrus cloud in the sky, they can cause a variety of interesting effects around the Sun. One of these are sundogs, or parhelia.
These are most often spotted 22º either side of the Sun, and can be bright spots or patches resembling a rainbow. Associated with them are the Solar Halos, where there is a complete hazy circle around the Sun, again at about 22 degrees from it.
As the sun gets low in the sky you can also look-out for the Sun Pillar, a column of light extending upwards by around 5 to 10 degrees. If you’re really lucky, you might even get to see the ‘green flash’ – are rare phenomenon seen just as the sunrises and sets, where a flash of green light appears just above it on the horizon.
Sometimes the clouds themselves – bane of every astronomer’s life – can appear beautiful, such as iridescent or the rare nacreous clouds, sometimes called mother-of-pearl clouds.
These can be seen a couple of hours before sunset and into twilight and are clouds which are higher up meaning when the sun is low they are illuminated from the bottom creating vivid colours.
Other clouds can also give rise to rays of light known as crepuscular rays, when the Sun is hidden behind a dark cloud.
It’s also possible to see the International Space Station during some of its daytime passes, particularly when it transits across the Moon and Sun. It’s even possible to see some meteors during the daytime, if you happen to be lucky enough to catch them – though you can always set up a radio meteor detector to detect them 24/7.
Whatever your passion, there is still plenty to look out for in the daytime sky so go on, check some of them out and let us know how you get on.
Paul Money is an experienced astronomer, BBC Sky at Night Magazine's Reviews Editor and author of the annual stargazing guide Nightscenes.