April 17, 2014

Astro-Challenge: Daytime Planet Spotting!

A daytime Venus post-occultation in 2007!

(Photo by Author).

Here’s a fine neighborhood experiment to try. Next time the Moon is around 1st or Last Quarter, show your neighbors or passers-by its pale silver disk hanging in the cool blue sky. Did they know that the Moon can be seen in broad daylight? Perhaps not, but did you know that with a little practice you can see many of the naked eye planets in the daytime as well? Starting this week, spring of 2012 offers several opportunities to perform these feats of “astro-athletics…” using that handy visible Moon as a guide… the only equipment required are a good pair of eyes, perhaps a decent set of binoculars, and patience.


To stack the odds in your favor, a sharp, deep blue sky offers your best chances of success. Higher elevation, if available, will also help. To check the sky transparency and seeing, block the Sun out with a building or a flag pole. Does the sky look a “washed out” white or solid blue, almost right down to a few degrees from the solar disk? If so, you’ve got good transparent skies for daytime planet spotting. Use of a variable polarizing filter, polarized sunglasses, and binocs can also help.

Tools of the daytime planet-spotting trade… note the high-tech “1x TP finder”!

(Photo by Author).

First up in brilliant +4th magnitude Venus. Currently setting three hours after the Sun for middle northern latitudes, Venus is racing rapidly northward reaching its most brilliant during late April at -4.7 magnitude and its most northerly declination for the remainder of the 21st century at 27° 49’ 01” on May 5th. (It may also be just possible to spot a daytime Venus 32° degrees east of the Sun during the annular eclipse this spring on May 20th!) This means that Venus will be transiting the local meridian for mid-northern latitudes several hours after the Sun and present a fine daylight target. The 4-day old Waxing Crescent Moon will be 2.8° north of Venus on the evening of February 25th, and will provide a fine introductory guidepost into daytime planet spotting. The Moon also provides a good focusing point for your eyes against the featureless blue sky. Blocking the Sun (A MUST if you are sweeping the sky with binocs!) with a building to the West also helps. Once you get a glimpse of Venus in the daytime, you’ll be amazed at how simple this feat is-a great thing to amaze your friends with. I’ve watched the Moon occult Venus in the daytime from our camp on Saint Froid Lake on northern Maine in 2007, and managed to catch Venus pass through inferior conjunction from Alaska in 1998! This is possible because the orbit of Venus is tilted 3.4° degrees in relation to the ecliptic. Thus, when said maximal tilt occurs during inferior conjunction, the razor thin crescent of Venus is just visible over 5° degrees above the horizon at sunrise for high latitudes, as will occur again on January 11th 2014. Venus reaches 50% illumination at magnitude -4.2 on March 29th, 2012 and will begin to show a crescent phase of its own as it slides towards a fine transit of the Sun on June 5th-6th, the last until 2117. Other fine dates that will see Venus near the Moon this spring are March 26th (with Venus 1.8° degrees North) April 25th (5.6° North) and May 22nd (4.6° North). A fine occultation of Venus by the Moon 4 days prior to New also occurs for North American viewers on August 13th. Such daytime conjunctions of the Moon and Venus may well have been the source of medieval pre-telescopic sightings of “apparitions near the Moon” as occurred on January 13th, 1589, for the town of Saint-Denis, France.

Jupiter, Venus, & the crescent Moon form a 10 degree “ring” on March 25th.

(Graphics created in Starry Night by Author).

Next up in order of difficulty is the giant planet Jupiter. Currently at magnitude -2.0, this world isn’t difficult to nab in the daytime with binoculars if you know exactly where to look for it, such as 4 degrees south of the five day old crescent Moon on the 26th of February. For contrast, the apparent diameter of the Moon is about 0.5 deg across, thus Jupiter will be 10 Moon diameters (about half an open palm’s width at arm’s length) away. Once you’ve located a ghostly daytime Jupiter with binocs, try finding it with the unaided eye. Cupping your hands around your eyes or using a “1x finder” such as an empty toilet paper tube (!) can help create that “Looking up from a well effect” first noted by Aristotle in the curious endeavor of daytime planet hunting. In 1998 I once managed to catch Jupiter near opposition from the Arm-End-of-Runway at Al Jaber, Kuwait noting its position in relation to a flag pole after sunset and then scanning the horizon for it the next evening 10 minutes prior to sunset. Another good attempt comes this year on March 14th with Jupiter just 3° degrees south of brilliant Venus, with both joined by the Moon on the evenings of March 25th & 26th. Interestingly, a series of 8 lunar occultations of Jupiter for 2012 begins on June 17th. Jupiter reaches superior conjunction on the far side of the Sun on May 13th, and opposition for 2012 occurs on December 3rd, providing another fine attempt to spot the planet in the morning daylight when the waning gibbous Moon slides by it just days prior on November 29th.

The near-Full Moon & Mars on March 7th.

Climbing down the magnitude scale, it is just possible to nab a daytime Mars under the right conditions. I successfully accomplished this during the outstanding 2003 opposition from Vail, Arizona when the waxing gibbous Moon lay near the Red Planet which shined at magnitude -2.7 just 10 minutes before local sunset. The local circumstances for the 2012 opposition aren’t quite as favorable as Mars shines at -1.2 about 9° degrees to the north of the waxing gibbous Moon a day before Full on March 7th, only four days after opposition. A similar situation occurs one lunation later slightly higher in the eastern sky at dusk on April 3rd.

Mercury reaches its best elongation for 2012, pictured here with the Moon on April 18th.

And finally, the ultimate challenge; sighting the planet Mercury in daytime skies. Mercury, you say? Isn’t that tough enough to see at dusk or dawn? Writer Stephen O’Meara notes in his June  & December 2005 Sky & Telescope column that this feat may just be possible near greatest elongation of the planet. With a maximum possible separation of 28° degrees from the Sun, one should try to sweep the daytime sky for the innermost world during local solar transit of the meridian at a time when the planet lies to the east or west of the Sun. Apparitions of Mercury vary greatly because of its elliptical orbit, which is the most eccentric of the planets in our solar system. An 18.2° degree eastern elongation of a -0.1 magnitude Mercury occurs on March 5th to practice on, but the best attempt this year will be the April 18th morning apparition 27.5° degrees west of the Sun, with the crescent Moon within 10° degrees away… can you follow +0.6 magnitude Mercury into the daylight? Again, physically blocking out the Sun for such a feat of astro-athletics is paramount; you don’t want to catch a blinding glimpse of the Sun in your optics, not even for a second. Positioning a building or hill between yourself and the Sun is your best bet; just remember that the rising Sun will also eventually clear those structures! A runner-up rain date for daytime Mercury-spotting occurs on July 1st with an evening elongation of 25.7 degrees east at magnitude +0.7 in evening skies.

…and this makes one wonder; would sighting Saturn, the final of the classical planets, ever be possible in the daylight? Well, the ringed planet does reach opposition on April 15th at +0.7 magnitude, just a bit fainter than difficult Mercury… any takers?

Why bother with these feats of faintness? Well, first this shows the limits of what the human eye is capable of. I’ve even shown planets to folks during star-parties hours before the Sun has set, allowing the telescope to track them into dusk. Also, these types of sightings demonstrate just what some of those curiosities and unexplained aerial phenomena seen in the daytime skies by peoples of yore might have been… now, if you see a flaming cross with an inscribed banner emblazoned across it hovering in the sky, that’s another matter all together…

Let us hear of your tales of daytime planet sightings this coming spring; such feats represent the cutting edge of visual athletics!


  1. [...] -      30th: Venus reaches greatest illuminated extent at -4.5 magnitude, bright enough to be visible in broad daylight. [...]

  2. [...] show a tiny dot of a disk. A fun project to try near opposition would be to spot the planet in the daytime with the Moon nearby as occurs on March 7th. I once accomplished this feat during the opposition of [...]

  3. [...] First up is an occultation of Jupiter on September 8th at ~11:00UTC. This will occur just past sunrise for viewers in South America from Ecuador southward; the rest of us will see a less than one degree pass of the pair. The Moon will be 51% illuminated during the event and reaches Last Quarter phase on the same day at 13:15 UTC. What’s interesting is that Jupiter should be bright enough at magnitude -2.4 to spy just above the Moon with binocs or perhaps even the naked eye in the broad daylight. [...]

  4. [...] east for the pair at sunset. In fact, this is also a great time to try and pick out Jupiter in the daytime, a feat that is made simpler by the nearby and easy to spot Moon. Use binoculars to guide your eyes [...]

  5. [...] fret not; you may still be able to spot Jupiter near the Moon on the 18th… in the daytime. Daytime planet-spotting is a fun feat of visual athletics, and the daytime Moon always serves as a [...]

  6. [...] of -4th magnitude, about 16 times brighter than Sirius, the brightest star. Venus can also be visible in the broad daylight if you know exactly where to look for it. A simulation of the view at sunset along the China-India [...]

  7. [...] will also present a good chance to see Venus during the daytime, using the nearby crescent Moon as a guide. This is a fun thing to try, and no gear is required! [...]

  8. [...] Moon will thus make an excellent guide to spot Venus in the broad daylight. It’s even possible to nab the pair with a camera, if you can gauge the sky conditions and tweak [...]

  9. [...] six degrees from the planet Jupiter. This presents a fine time to try and spot the planet in the daytime to the Moon’s upper left, just a few hours prior to [...]

  10. [...] 24- The waning crescent Moon passes within a degree of Venus, a great time for spotting the planet in the daytime. [...]

  11. [...] 24- The waning crescent Moon passes within a degree of Venus, a great time for spotting the planet in the daytime. [...]

  12. [...] second and third brightest objects in the night sky. This will also be a fine time to attempt to spot Venus in the daytime, using the nearby crescent Moon as a guide. It’s easier than you might think!  In [...]

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