Ultra Venus

Perhaps no other object has such a wide gulf between its naked eye impression compared to its appearance in a telescope than Venus. In our twilight sky Venus demands attention, shining like a brilliant diamond. Whenever the crescent Moon stops by for a visit, I am always up for grabbing a few shots (even though I already have many prior encounters documented). And when our sister planet pairs with another planet (as it did earlier this year with Jupiter) or the Pleiades, amateur astronomers turn into paparazzi and flood the online galleries with their glamor shots.

Venus & Jupiter Feb 28, 2023

But few of those amateur astronomers will tarry very long with Venus in the eyepiece. The view is that of a dazzling, featureless cue ball emulating one of the Moon’s phases. Nothing stands out so it’s a quick check-in and on to something of greater interest.

With patience and some filtering there is more to see. A deep violet Wratten #47 filter not only knocks down the glare but provides subtle boost to the very low contrast features in the Venusian clouds. While at times one might make out a dusky region on the planet, the most common feature that appears is a brighter region at one (or both) of the poles. Know as a “cusp cap” it is an actual feature and not just an artifact manufactured by our brain. Large Hadley cells rise high into the atmosphere from the hot equatorial regions and then sink back down in the high temperate latitudes, forming a slightly darker “cusp collar” bordering the cooler cusp cap.

Planetary imagers also find themselves stymied by Venus’ reluctance to share features. Like most others, my prior attempts to record details on the 2^nd rock from the Sun using “lucky imaging” techniques produced crisp but bland captures of the globe.

Our professional brethren have also struggled with Venus until about a century ago when astronomer Frank Elmore Ross targeted it using Mount Wilson's 60- & 100-inch reflectors. His gig before that was a decade at Eastman Kodak studying photographic emulsions and filters, which led him to make photographs in IR and the newly released UV filter. While the IR failed to penetrate the cloud layer to show details as he had hoped, the UV unexpectedly did. Curiously, there was not much follow up to his discovery until images acquired by French amateur Charles Boyer nailed down a rotation period of about 4 days. His results were published in 1960 in Icarus (and rejected by none other than Carl Sagan). While radar data eventually established a retrograde rotation of 243 days for the planet, Boyer’s observations of a 4-day “super-rotation” of the Venusian atmosphere were eventually confirmed by Mariner 10. Thus we end up having two longitudinal “systems” for tracking central meridian on Venus: CM I for the surface, and CM II for the upper atmosphere clouds.

Over the last ten years amateur planetary imagers have gradually been targeting Venus using a UV filter and getting some nice results. UV filters are pricey (north of $200) and sometimes backordered for months. I finally budgeted for the Atrodon UVenus filter which was heralded as having some of the best UV transmission. Renowned imager Damien Peach put together a video on his patreon channel that provided further tips on obtaining a successful UV image such as combining it with an infrared blocking filter since many UV filters leak IR which can smear the image.

Sample transmission for UV filters

With Venus approaching its greatest eastern elongation (distance in our sky) from the Sun, it was time to try again to capture cloud details on our neighboring planet. Starting at sundown I worked on centering the planet with good focus to begin acquiring my UV videos. Reasonably calm seeing is really important for achieving that focus and often not present when dealing with an object like Venus that is never more than about 40° high, but I finally got that on my May 15^th session. I confess that I was pretty ecstatic being able to make out what seemed to be a southern cusp cap on the image shown on the laptop during acquisition, implying I would have something worthwhile to work with. And the next day when putting the video through my processing workflow I ended up with a nice result, clearly showing north and south cusp caps with some of the darker collar. The center of the planet shows segments of lighter and darker clouds.

Venus May 15, 2023 in UV

In my researching about capturing Venus in ultraviolet I came across a few sources that argued that introducing any sort of lens element in the imaging train (e.g., a Barlow lens, an SCT corrector plate) was to be avoided if possible since these can cut down on the amount of UV light considerably. The ideal situation is a mirror telescope such as my 10” Newtonian. For the heck of it I did a capture at the end of the session using the Barlow. While the seeing may have deteriorated by that point, my results certainly seemed to confirm that the benefit of a larger image was far offset by the decline in sharpness of the low contrast cloud features.

So, what do the darker regions represent? In classic Venus fashion the planet will not give up that information yet. Some scientists believe that it is a photochemical reaction in the atmosphere that results in UV absorbing material. However, there are even some who argue it could be cloud based microbial life generating these regions and liken it to algae blooms that we see here on Earth. With a bevy of spacecraft heading Venus' way later this decade we may eventually get an answer to this question.

As usual I submitted the final results to ALPO. A few hours later I heard back from Julius Benton, the Venus section coordinator. “Thanks. Your UV image looks very good!” was great feedback to receive, and confirmation that the multi-year journey to acquire the equipment and knowledge on how to make Venus finally give up some details was satisfying indeed.

Something to Crow About

There is real joy when the pleasant spring weather sets in, providing evenings of cool temperatures that I can tolerate with only a light jacket but the bugs cannot. Our garden spotlight softly illuminates the beautiful azalea newly flush with coral colored blossoms and the nearby deep purple irises. The distinctive clink of an aluminum bat connecting with a pitch let's me know that nearby Towson University is having a game this evening. Well, that and their stadium lights lighting up the tippy top of the trees in the field behind my house is also a dead giveaway. 

After setting up the scope I minimize what light pollution that I can by turning off the yard lights. This evening I'm hunting Crow - some celestial highlights of Corvus as he wings his way towards a midnight rendezvous with the meridian. As my night vision slowly improves I struggle a bit to discern the outline, a geometric pattern of half a dozen 2nd-4th magnitude stars. 

The first stop is an eye-catching asterism known as the Stargate. Lying roughly a degree southwest of M104, there is a good chance you may have already stumbled upon it when looking for the Sombrero galaxy. One could probably sweep it up in a star hop by extending a line from k Virginis and Spica westward about 12°, but I take the easy way out and key in the coordinates. At times with a computerized mount you feel like Picard on the Enterprise, barking out the location and issuing a "make it so!" pronouncement. 

At low power in the 10" Newtonian it is delightful - a triangle of stars within a triangle, each having one of the triad much fainter than the other two. Not really seeing any color here but the arrangement is very cool. A little higher power makes it easier to see the fainter members of each of the dual triangles. So what the heck is a "stargate"? Well, near as I can tell, this is a reference to the spaceship portal used in the 80's sci-fi series Buck Rogers in the 25th Century. Hey - if the Greeks can fashion a crow from a trapezoid on a stilt then a "stargate" ain't half bad!

From an easy asterism I go in search of my next objective - planetary nebula NGC 4361, an entry in the Herschel 400 list. If you can see the top of Corvus' trapezoid it would likely be fairly easy to target this with a Telrad. However, the scope is well-aligned so I succumb to the GoTo siren and ask it to do the work for me. I inspect the field at 25mm without any filter, but there's no sign of anything unusual in the eyepiece. Adding the Lumicon UHC and studying the area once more leads me to believe that there is a faint dab of light when using averted vision. Taking the magnification up to 95x with the 16mm + UHC filter darkens the background a bit more and makes me far more certain that I’ve got this 11th magnitude planetary. I use my makeshift drape/balaclava to block out extraneous light in hopes of getting a better look and maybe even catch the central star which is an incredibly hot Wolf-Rayet star, checking in at 270,000° Kelvin (compared to our Sun at about 5,700° K). While I can see the glowing orb a little better it fails to tease out the nebula's progenitor. The nebula appears circular and fairly evenly illuminated, perhaps twice the size of Jupiter. While given the moniker of "The Water Sprinkler" based on images of it that show internal detail, in my scope I discern a faint, glowing orb best seen with averted vision and lacking any structure. The field it is set in is very sparse, made more so due to the use of the UHC filter.

Next in my Corvian exploration is S1604 (Struve catalog entry #1604), one of the targets listed in the AL's Double Star program. This double is not in a very friendly star-hopping  location with multiple other similar stars near it and no solid anchor point to start from. It isn't listed among the keypad’s roster of double stars, so I do a quick lookup of the RA and Dec and key the coordinates. Having expended the effort at the outset of the session to get a good alignment pays dividends as the scope dutifully moves to the spot. Looking over the field at 25mm there are a couple of candidate suns that may be the target, and I think I see one of them as a double. Bringing the magnification up to 156x and revisiting each one I quickly confirm the right one. S1604 reveals itself as a splendid triple system that closely replicates a right angle. The two comes are very close in magnitude with the brighter one making a N-S alignment (PA ~0°) and the other E-W (PA ~90°) with the primary. This is curious, as Burnham's Celestial Handbook lists the position angles as 91° and 73°, clearly at odds with what I am seeing (and what is listed in the AL Double Star program list). Why the difference - is it an errata in Burnham's? I find it hard to accept that the stars changed position that much (especially given one of them is believed to be an optical alignment rather than a true common pair). Not sure that I am picking up any color here, although the faintest of the trio might have a ruddier glow to it.

Saving the most challenging for last, I set off for the Antennae galaxies - NGC 4038 and 4039. This duo of roughly 10th magnitude interacting galaxies should be doable in a 10" telescope, but the challenge becomes plucking them out from the bad light pollution. While the GoTo had been doing very well, for this item I decided to use my star hopping skills to have certainty that I was over the target. Locating TY Crv lying west and midway between g and e Corvi, I nudge the scope northeast until I encounter the 8½ and 9½ magnitude pair of SAO 157047 157046. From there it’s almost due north to HD 104496 and SAO 157048 where the galaxies should be found more or less midway between these two stars. I navigate the route with a high degree of confidence, reaching the endpoint and earnestly scanning the eyepiece field. Alas, there is nothing there to greet me. I check carefully with the 16mm and then the 9.7mm eyepiece, and then repeat the process using the Baader Moon & Skyglow filter. I even grab the balaclava once more to shield my eyes from extraneous light, but there is simply nothing to be had. Perhaps another, clearer evening, or waiting to try in early morning hours next winter, would bear fruit. Sadly the light pollution wins this round.

Star hopping to the Antennae

It's been a very satisfying evening under the stars with my feathered friend. While I'm tempted to continue looking for other spring objects in the area I decide to pack things up since I'll need to be at work in the morning. And that is part of the beauty of our hobby, the heavens (usually) will offer you another opportunity to explore its wonders, even amid suburban skies.

Under the Influence

The Howard Astronomical League lost one of their luminaries last month with the passing of Bob Prokop. The club never had a more ardent supporter than Bob, serving in the leadership role as a club president and supporting many of the club's outreach activities. He loved our hobby and it showed in many ways.

While I never had the opportunity to develop a personal relationship with Bob, I was certainly under his influence. He had the ability to advocate for the spectacular above us as well as the sublime. Was Mercury having a favorable apparition? Bob would be posting about it in the email group. Was the Moon's libration tilting a far-flung crater into a better position for us to grab a look at it? Our lunar expert knew the when, where, and how of the circumstances. On more than one occasion his exhortations found their mark and nudged me outside to hunt down what Bob was showcasing.

Bob was indefatigably upbeat about any clear night. Do NOT complain to him that the full Moon was ruining the evening lest you be embarrassed by Bob's retort as to the lunar features, asterisms, or other bright destinations that would not be suppressed by a glorious full Moon. And everyone in the club knew that he wasn't Googling that information, it simply flowed effortlessly from his years gazing up at the heavens. I still recall a passing comment that I made - something along the lines of "only a mediocre double star" - to which I was called to account in a most affable manner.

One thing that Bob and I were resolutely in lock step on was the value of star-hopping. We both cut our astronomical teeth by using instruments that required you locate your object rather than simply dialing it in. To quote Bob, "Of course, I am also the nut who has my telescope on an unmotorized alt/az mount with no finder scope... and can still find that 9th magnitude star faster than anyone with their fancy go-to software!" No brag, just fact.

I understood his lament that "today's kids" miss the anticipation and preparation involved when stalking a faint object, not to mention the thrill and sense of accomplishment when it finally appears in your eyepiece. Plus, who knows what stary vistas and uncharted beauty you may encounter along the path to your objective? While I have succumbed to the GoTo siren with my latest mount, I still do put the keypad down at times and drive myself to my destination. 

While my interactions with Bob were virtual, they were valued nonetheless. He was a welcome inspiration and source of knowledge for me and many of my club peers. He was one of those special people I've had the good fortune to come across who's love of the night sky was palpable and contagious. 

Getting Started

It's a question that I (and most amateur astronomers) get from friends from time to time: "I want to look at stuff in the sky - what sort of telescope should I get?" It is a tough question to answer because there are a multitude of variables (like how dark your sky is), a wide variety of celestial objects for which each has a "best" instrument, and the prospective user's existing familiarity with the night sky. 

It is understandable why folks get the urge to grab a scope and go out into the night. The images sent back from our spacecraft are stunning to say the least. And while most people grasp that their telescope is going to fall short of a billion dollar scientific instrument, they likely also have acquaintances posting to Facebook or Instagram with some pretty cool stuff. That's part of the problem with social media - it makes stuff look easy since we only display our victories, not the flubs we made getting there.

OK, so rather than totally dodging the question with a "it depends..." answer, let's consider the following scenario. We have a newbie who really knows very little about finding things in the night sky and who lives in suburbia (where their sky is not going to be bleached out by a ton of lights). They'd love to see a galaxy, some beautiful star clusters, and maybe a nebula (gas cloud) or two. They'd like to see Saturn's rings and Jupiter's Great Red Spot.

Those two sets of objectives (Deep Space Objects [DSO] and Solar System Objects) are somewhat mutually exclusive for our beginner. DSO present the challenge of being faint and potentially very difficult to find for a new telescope user. Of course you can buy a scope with computer assisted GoTo that will point the telescope to the object if you can align it properly (not to mention that you'll be jumping into the hobby for a much bigger financial bang). 

Planets, being brighter, are much easier to find with your telescope. However, features like the polar ice caps of Mars and the belts of Jupiter are more subtle than you might imagine to pick out with your eye. It's almost like playing an instrument with planetary observing - you need practice before you can detect some of the cool things your telescope can show you.
So - how can you break into this hobby without breaking the bank? The answer lies in a nice set of binoculars. Most people don't even consider them because they believe they are not powerful enough. The truth is that their wide field and additional light gathering power will indeed open up a lot of celestial DSO for you. They have the added benefit of being user friendly - no need to align anything, just pick them up and step outside to begin exploring. And - they pack easily for that trip to the beach or the mountains where the skies are much darker than at home.

There are a lot of sites with binocular recommendations. One thing to know up front is that the first number in the binocular description is the magnification (or power), the second is the diameter of the front lens (larger diameter = ability to see fainter objects). I personally own two pairs: a 7x50 by Celestron and a 15x70 by Oberwerk. The former are reasonably light and easy to use, the latter are a bit heavier but give wonderful views. I'd recommend a 7x50 or 8x56 for someone starting off - something you should be able to do for under $150 easily.

Binoculars - ready to go & user friendly!

"Sky Safari" App

Equipment is only half the battle. The really important thing is to begin to learn your way around the sky so that you can find things to look at. You don't need the binoculars to start this, your eyes and a star chart (or, even better, an app on your smart phone that can simulate the sky where you point the phone) are all you need. Start learning to identify the bright stars, then trace out the other stars in the constellation that has the bright star. From there see if you can locate stars in some of the dimmer constellations between the bright stars. As you do this you'll also become familiar with how astronomers quantify the brightness of an object (its "magnitude"). Once you've made friends with the stars overhead you can use them as markers to find the more interesting stuff.

Like what? Well, on a crisp February night you could swing by the Orion Nebula, a hydrogen gas cloud birthing new stars. Or high up in the sky catch the Seven Sisters (Pleaides), a beautiful collection of diamonds in the sky. For something more subtle you can track down the oval smudge of light that is the Andromeda galaxy lying some 2 million light-years from Earth. And since Jupiter is out in the evening sky take a moment to check it out - you may not see the Great Red Spot but you'll likely get to see some of its moons very close by as little stars. For other ideas I'd suggest picking up a book such as Touring the Universe Through Binoculars and let it guide you to a lot of fascinating destinations.

The tiny cloud represents the Orion Nebula
(It looks much better from dark skies)

An important lesson that you'll quickly learn is that when it come to the night sky a camera is much better equipped to show color and detail than our eyes. The camera opens its lens and collects light for many seconds, our eyes take an instantaneous reading of the photons. As such you'll not see the pinkish tinge in the Orion Nebula nor the spiral arms of Andromeda. But, you still do get to see them first hand, and that can be rewarding and exciting as well.

Orion Nebula - 2 sec Exposure

If you are still at it with your binoculars some 6 months later and you want to take the next step, then I'd say invest in a telescope. A great idea would be to go to a local club's star party and look through a variety of telescopes. But even if you can't, you cannot really go wrong getting an uncomplicated Dobsonian telescope in the 6-10" mirror size range. The additional light gathering power and magnification will open up a much larger range of DSO that you can hunt down from your yard.

Of course if it turns out that the thrill of seeing faint fuzzies in the sky does not give you the satisfaction you were hoping for the binoculars can always be used for checking the wildlife in your backyard - or getting an up close look at the horse you're betting on in the fourth race at Pimlico. 😏

C/2022 E3 (ZTF)

Last March the folks at the Zwicky Transient Facility picked up an object using their wide field survey. It was soon determined that this was a comet heading inbound for a rendezvous with the Sun after a 50,000 year absence. The orbital calculations along with the comet's brightness led astronomers to predict that C/2022 E3 (ZTF) might become a naked-eye object soon after its perihelion on January 12th, peaking as it makes its closest approach to Earth on February 1st. Given it's the brightest comet to grace our skies since Neowise in the summer of 2020 I thought it was worth trying to observe it and possibly get an image or two last Friday.

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Jan 27, 2023 21:45 ET from Towson, MD
Clear skies, 35°F with light wind
Seeing 3/10 Transparency 9/10

First up is a quick scan of the area just a little NW of β Ursae Minoris (Kochab) using the 15x70 Oberwerk binoculars. At 2nd magnitude and a deep orange color it is easy to pick out Kochab from even my Bortle 8 skies to start the brief star hop. A little pan to the right and up and I can quickly see what appears to be a tiny, weak nebulosity. Working to hold the binoculars steady enough to get a good look I confirm that we have a comet that should be an easy target.

Rolling the 10" Cyrus Newtonian out I ditch getting 2-star alignment in favor of just using the finder scope to target the fuzzy visitor. It's readily visible in the spotting scope so it doesn't take long to sweep it up in the 40mm eyepiece. It's set in a nice star field and there is a star-like nucleus along with a diffuse, weak haze representing its coma. No real color can be discerned. Bumping up to the 25mm Plossl to darken the background a bit the coma is a little easier to see but in all honesty I cannot make out any shape to it that would let me guess as to the presence of a tail and its direction. It certainly seems to be at about 5th magnitude as predicted.

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To round out my ZTF session I grab my Canon camera and put the kit 70-300mm lens on. This time I try to avoid focus issues by targeting the almost 1st quarter moon and dialing it in to be as sharp as possible. At 200mm focal length I should get a reasonable size for the comet, and the rule of 500 suggests an exposure of 2½ seconds. But a quick test exposure shows unacceptable trailing at 2 seconds, so I drop it back to 1 second and begin firing off pictures, accumulating about 100 of them. From there I drop the focal length down to 70mm and run a series of 6 second exposures before calling it a night.

A few months ago Sky & Telescope ran a nice spread on nightscape photography. Among the tools that they mentioned was Sequator, a free program that I had not heard of before that stacks your images and can "freeze" the foreground. Sounded like a perfect tool to use for my ZTF images, so I downloaded and did a quick YouTube video to get me oriented to its use. I have to say it was much easier and faster than my standard go-to in this scenario (Deep Sky Stacker), although it could not keep my foreground tree from blurring, likely because of the breeze shifting its branches. But the resulting TIF yielded a very nice result after having some tweaking in Photoshop, especially given the minimal effort I put into the capture.

While the comet is outbound to the Kuiper belt deep freeze, we do have a couple of opportunities to get some interesting shots of it as it photo-bombs a few celestial luminaries as it leaves the stage:

Feb 6: The comet swings close by Capella

Feb 11: ZTF buzzes Mars

Feb 15: The green ghost will contrast nicely with nearby Aldebaran

While comet C/2022 E3 ZTF is likely to fall short of the media hype, it still is an interesting and readily accessible example of what most comets look like - star-like nucleus encased by a puffy, tenuous cloud. 

The Pixel Sweet Spot

Earlier this week the forecast was for an evening of average to perhaps better than average seeing with cold (but not biting) temps. I rolled out the scope a little before sunset to begin cooling and got things ready - with Jupiter just past quadrature it is always going to be highest in the sky as soon as it becomes visible. 

I did the routine alignment, collimation check, and finder alignment before finally popping in the ZWO camera. Activating the camera I was greeted by a strange sight - an emerald green Jupiter. At first I thought maybe a Debayer setting was off in the capture interface but soon noticed that the histogram was not registering in blue or red, only green. I rebooted the laptop hoping maybe that would restore things, but no luck. I brought up a different capture application, but it, too, sported a green globe.

Rather than admit defeat I located my retired Imaging Source camera and popped it into the Barlow. The view and histogram confirmed that we were back to getting a color image, but I immediately was struck by how much smaller the image appeared to be. Hmm - what was that about?

It turns out that my older camera, a DFK21AU042, has a pixel size of 5.6µ whereas my ASI178MC has a size of less than half that, checking in at 2.4µ. The formula for calculating how much sky each pixel registers for your setup is as follows:

  (Pixel Size/Telescope Focal Length) * 206.265  

For my setup using a 2.5x Barlow that becomes:

DFK21AU042 = 0.31"

ASI178MC = 0.13"

The theoretical ideal for planetary imaging for under average seeing conditions is around 0.15" per pixel (Note that this is different than DSO imaging, where the average is about 1-2" per pixel). Clearly, my ZWO camera is a lot closer to the mark, and the better thing to have done would have been to stop and swap out my 2.5x Barlow for my 4x one to get a little lower arc-second/pixel value. But the window of calm seeing that we often get shortly after sundown wouldn't allow that, so I forged ahead.

Below are comparative images taken about a week apart of roughly the same Jovian longitude. It is pretty obvious from it that we lose resolution in the image acquired using the DFK21AU042 camera.

Is the image from the older camera terrible? No, hardly. We can still make out details like Oval BA and anti-cyclone storm A1 - something that was unheard of using film a few decades ago. But in astronomy, and in planetary imaging in particular, it is all about getting all the parameters as ideal as possible so that you can capture all the details available given the seeing conditions. Hopefully I get my ZWO camera fixed, but in the meantime I know from experience now to at least break out the 4x Barlow to try to get closer to that desired arc-second/pixel value.

Frost Moon Eclipse

For the second November in a row, the Moon was scheduled to take a plunge into the Earth's shadow (only this November it'd be a total eclipse rather than a very near total eclipse). With the forecast for the early morning of November 8th being a bit questionable (and not taking the workday off), my plan was to set an early 5am alarm to check the western sky for clouds. The weather gods ended up being kind as I could see the eclipsed Moon hanging low in the sky with minimal clouds. I threw on street clothes, grabbed the camera waiting on the tripod in the kitchen, and headed out to locate a spot along the street with an unobstructed view of the event.

It was chilly but not frigid (50°) with some scattered clouds amid a pretty transparent sky overall (7/10). There was a sporadic breeze out of the north. I took some time to just visually enjoy the sight of the deep orange lunar disk hanging about 10° above the western horizon between a gap in the trees. It seemed to be a little on the dark side as lunar eclipses go, probably a Danjon 2 by my estimate. I thought about how these events are beautiful occurrences to us but that centuries ago they would likely strike fear and dread to the average person. Iconic Taurus and Orion looked on nearby along with brilliant Mars, but the spot occupied by Luna was devoid of visible stars given my Bortle 8 suburban skyglow. 

 

 

I racked the telephoto out to 300mm and worked on getting a focus. I then started firing off a set of shots, altering the exposure time to hopefully get one close to approximating the visual appearance. I then dropped the focal length down for some wide-angle shots before calling it a successful event as the Moon slid further to its approaching western horizon rendezvous.

Downloading the shots to the computer showed that, yet again, I had managed to just miss the desired razor-sharp focus. To me this is the Achilles Heel of DSLR cameras – they excel at allowing multiple photos without worry of film expense and even a digital darkroom, but gone are the days where you could reliably slide the focus ring all the way over to infinity and know that you were indeed focused at infinity. Some of it might have been that northerly wind buffeting the tripod a little, but probably 90% of the issue was my not being attentive enough to the focus.

 

I wonder how many lunar eclipses I’ve now taken in over the years. It would be hard for me to go back and tally them as earlier on I certainly didn’t keep records, at least nothing that survived till now. Whether it’s 10 or 20 I can certainly say that they are one of the most pleasant spectacles that Mother Nature provides.