Jupiter in Broad Daylight

Moon and Jupiter before sunset, 14 April 2013April 14, 2013 Update: Last month the Moon passed Jupiter at a time that allowed (relative) easy sighting of Jupiter in broad daylight…. with the unaided eye. In fact it was the best opportunity for several years to come.

(The image here represents the relative position of the Moon and Jupiter about a half hour before sunset today as seen from Denver. Specifically, the view is facing West at 7:07 p.m. MDT, about 47 degrees above the horizon.)

But if you missed the chance then, try again today. The conditions are not quite as good, but throughout North America the Moon will be to the left (or slightly above and to the left) of Jupiter in the last half hour or so before sunset. The two will be separated by 3 to 4 degrees (6 to 8 lunar diameters), depending on the observers geographic location and time of observation.

Of course, the observation may be made earlier in the day, but the last half hour before sunset will generally provide the best chances, dependent on local weather conditions. I suggest setting the observation up in a good graphical planetarium program ("Starry Night" for example) beforehand. There are more observing suggestions in the original article below. (However, remember that the specifics listed below, including the graphics, are for the now past opportunity in March.)

April 15 Update: I tried several times yesterday evening, starting about 45 minutes before sunset, with no luck. Then I did indeed catch Jupiter, with the unaided eye, at 7:31 p.m., just 6 minutes before local sunset. Due to strong winds and probable dust in the air (or perhaps high thin clouds from an approaching storm system) the sky was less contrasty than it could have been. Aside from that, I suspect I would have caught it even earlier.


Not many know it and fewer have actually done it, but theDenver630pm planet Jupiter can be observed in the daylight sky under good conditions… with the unaided eye. Most everyone knows that the Moon can sometimes be seen in full daylight, and most amateur astronomers have glimpsed Venus once or twice with the Sun still in the sky.

Some have even reported observing the bright star Sirius in the daytime sky, although I have to say that if this is true, if must have been as a result of exceptional eyesight under remarkable atmospheric circumstances. In fact the academic studies I have read relating to the daytime observation of stars strongly suggested that no star is bright enough to be seen in the daylight without optical aid. Based on my experience I think this is true.

Three planets, however, can be seen if the conditions are right. They are Venus, Mars and Jupiter. Venus is not much of a challenge, and in fact is pretty easy if you know when and where to look. However, even at their brightest, Mars and Jupiter are only about one sixth as bright as Venus and present significantly greater difficulty. Seeing  Mars with the unaided eye in the daytime is not going to be reasonably possible for some time, so let’s just consider Jupiter.

If you have reasonably good eyesight, and know when and where to look, you can join a very small group of observers who have caught the giant planet in broad daylight, without a telescope. Although I have yet to observe Mars in the daytime (haven’t actually tried), I have clearly and distinctly observed Jupiter 3 times in daylight over the same number of decades.

So how do you do it? As with many things, it’s all about timing. First and foremost, you must find a time when Jupiter is as high in the sky as possible just before sunset. In general the sky is not as bright in late afternoon as it is at midday, so Jupiter will stand out better in contrast. Being as high in the sky as possible ensures that Jupiter’s light passes through the smallest column of air before it reaches your eyes, minimizing absorption of its light. Essentially, what this means is that what you want to do is choose a time of year when the Ecliptic is highest in the sky at sunset (which is in the Spring) and when the Sun and Jupiter are in "quadrature," which is just a fancy way of saying that the two are separated by 90 degrees (or 270 degrees) in the sky. These conditions are met best during one spring every 12 years. (The years before and after are possible, too, those not as easy.)

As it turns out, March 2013 offers the best chance for the next 12 years. (Again, not the only chance, mind you, but the best.)

Now, to make it even easier, it would be nice to have a "landmark" in the sky to help you locate Jupiter. Enter the Moon, stage right. As it turns out, the Moon’s trajectory in the sky is very similar to Jupiter’s, so we need to pick a time when the Moon passes near Jupiter shortly before sunset.

All these factors come together this weekend, when the nearly First Quarter Moon passes near Jupiter, high in the southern sky shortly before sunset. Of course the Moon will be near Jupiter all night until they set around midnight, but you want to view in, say, the last half hour before sunset. Saturday, Sunday and Monday will do, but Sunday (3/17/2013) is by far the best day this time around.

Before observing, get a star chart showing the position of the Moon and Jupiter at the time you want to observe. You can get these in many software products, including a number that are free. (The graphic near the top of this page shows the Moon with Jupiter as a tiny speck above it, facing roughly South at about 6:30 p.m. Sunday as viewed from Denver. Click on it for a bigger view. Several other cities are listed below.)

Stand somewhere with a clear view of the southern sky, but out of direct sunlight or strong reflections.  It may help to “cup” your eyes or use some other method to reduce the excess light. Then locate the Crescent Moon in the southern sky at around 6:30 pm local time and scan the area with binoculars. Once you find Jupiter in the binocs, try it with just your eyes.

The previously mentioned image near the top of this page is a screen save from “Starry Night” software showing the Moon and Jupiter (small dot above the Moon) set for Sunday afternoon at about 6:30 p.m. as seen from Denver.

Here are screen saves for several US cities (use list view):

We have considered only late afternoon observations here, but similar reasoning holds for early morning observations. In fact, early morning observations are even easier in a sense because you can observe Jupiter or Mars before sunrise, then track it into the daytime sky. But for this time around, it is afternoon observations only.

Of course, if you have a "go to" telescope you can just find Jupiter that way, and then attempt an unaided eye observation. But frankly, I think that this is kind of copping out. Still, use a crutch if you must.

For more, see my article on EarthSky.org:

10 surprising space objects to see in the daytime sky

Postscript:

The exact appearance and orientation of Jupiter and the Moon in the sky may not be precisely as shown in the graphics, depending on the observer’s exact geographic location, time and direction facing. If you use a clock-face analogy, a straight up-down line defining the 6 and 12 positions may indicate Jupiter at, say, an 11 o’clock bearing from the Moon. However, a more accurate way of using these graphics is to imagine the 6-12 hour line on the clock face as running from the bottom cusp of the Moon’s crescent to the top cusp, and then orient the position of Jupiter based on that.

Also, scanning with binoculars is very helpful, but be sure you are accurately focused on the Moon first (to establish a clear focus). Even being slightly out of focus will blur the image of Jupiter and make it harder to see.

You might think that the best time to view Jupiter or Mars would be when the planet is at its greatest magnitude (brightness). Actually the magnitude of Jupiter doesn’t vary all that much, but Mars does. The problem with viewing at actual greatest magnitude is that for superior planets (those farther from the Sun than the Earth) this occurs near the time of opposition, meaning that the Sun and the planet are on opposite sides of the sky (like the situation with the Full Moon). Thus the planet will be rising as the Sun is setting, and at best the planet will be positioned very low in the sky in the late afternoon. The Earth’s atmosphere filters out a lot of the light coming from objects near the horizon, not just dimming them but also changing color and making stars twinkle. (Have you ever seen an orange or red Moon rising?) In addition, the effects of haze or pollution are increased near the horizon, dimming objects further. For these reasons, trying to observe Mars or Jupiter in the daytime sky at the time of a planet’s greatest magnitude may not be a good idea.

Some advocate using polarized glasses because they tend to darken the sky about 90 degrees away from the Sun, which in theory should increase the contrast between the sky and Jupiter. I have not really tried this method, but I note that using polarized glasses or a polarizing filter not only will darken the sky, it also will darken the image of Jupiter, making it even harder to see.

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About Starman

Cosmic Awareness Facilitator. Astronomy, space, physics, science, planets, cosmology, reason, logic, clouds, sky phenomena, the environment, dogs and other animals, and other interesting stuff.
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