Can We See Martian Craters From Earth? By: Jeff Beish (Revised 01/15/2019)
INTRODUCTION
Can we identify topographic features on the planet Mars using Earth-based telescopes? This argument has gone on for years and probably will continue even after counter proposals are offered here. It centers on claims by a small number of observers who have seen and identified craters, mountain ranges, canyons, volcanoes, and other Earth-like feature on the Red Planet Mars. An excellent illustration of how to identify an impact crater on a celestial object can be found here and here.
Most assuredly, if we are to compare the appearance of an impact crater on the Moon to one on Mars then the following criteria should apply: A crater should have a raised rim, walls, a floor, possible central uplift, ejecta and rays.
One should not forget that we are dealing with personal opinions and are often predicated on some loose and untried theories. To render an opinion on what someone else sees or does not see is difficult at best; however, we must follow conventional wisdom and what is known about the nature of telescopic observations. Theories vary from those that become "laws of physics" to completely wrong ones that defy replication. In any event, the discussions should not stray far from known and accepted facts. Of course, in the subjective minds of humans, who can define what a fact really is?
Prior to the Mariner-4 Spacecraft passing by Mars during 14-15 July 1965 speculation about the existence of craters on this Red Planet was confined to a small group of astronomers. Well known observers, E.E. Barnard and John Mellish, are credited with the supposition that Mars had craters even before space age technology took us out there for a closer look. The problem with their claim is; Mellish’s drawings and observing notes were destroyed when his house burned, or as the story goes.
Recently, Barnard's drawings and observation logs were recovered and from the preliminary reports no such evidence of Barnard’s crater sightings have been uncovered [Sheehan, 1995]. Without hard evidence, such as photographs, observational notes, or drawings with specific locations of these features, we cannot even begin to accept such claims.
Other notables have speculated that Mars was a cratered planet. In 1944 science writer D.L. Cyr, in the book Life on Mars, suggested craters on Mars. In the late 1940's and early 1950's R.B. Baldwin, C.L. Tombaugh, and E.J. Opik independently predicted the possibility of Martian craters because of its close proximity to the asteroid belt. However, NASA and other space scientists questioned this. If being clos e to the asteroid belt was a major factor in the number of craters on Solar System objects then the crater density should have be significantly greater on Mars, more so than on the Moon -- something they did not find. [Glasstone, 1968].
NOTE: Spacecraft images revealed new impact craters on Mars: see Malin Space Science Systems .
LIMITATIONS OF THE HUMAN EYE
Since the human eye is capable of resolving objects no smaller than about 62 seconds of arc we cannot identify objects such as craters on the Moon, the disks of planets or their satellites with the unaided eye [Sidgwick, 1980]. We can see gross albedo features on the Moon, such as the dark maria or bright areas; however, Lunar relief is just too shallow to be resolved with the human eye without an optical system to magnify them.
Planetary observers fantasize about being able to resolve Jupiter, Venus, or even Mars with their "naked" eyes, but it just isn't possible. Mars only reaches an apparent diameter of 25.1 seconds of arc during closest approach -- Jupiter and Venus only about 50 seconds of arc, we must use some instrument to magnify these objects. This is only common sense if we accept the conventional definition of resolution of the human eye [Sidgwick, 1980].
One interesting question should be asked; how do we identify a crater on another celestial body? The Moon has both craters and domes, so, how do we know which is a crater and which is a dome? When the Moon has a phase both features will have a bright side and a dark side. The obvious answer is to know the relative direction of Sunlight on the Moon or planet -- or find a mountain and remember which side is bright and which is dark. Then follow that convention to define craters and domes.
Adding to the difficulty of recognizing Martian craters is its atmospheric activity. Ground -based telescopic observers regularly report clouds and hazes in heavily cratered areas on Mars. Spacecraft data indicates the planet's surface is nearly always covered by a dusty veil, further lowering contrast and at times renders the surface completely featureless [Martin, 1994]. Unlike our Moon with its sharp crater boundaries, Mars has been subjected to billions of years of wind erosion, leaving its crater walls rounded and floors filled with dust.
Figure 1. Cut away drawing of typical Martian crater. Drawing shows an average large Martian crater, such as Huygens (304ºW, 14ºS), with a depth of 3-km and diameter of 500-km. Maximum shadow for 47º phase defect = 3-km x sin 47º = 2.2- km.
Another important aspect must be considered -- contrast. Even if we could resolve such topography on Mars as described above, would there be enough contrast between the shadowed or sunlit walls and the crater floor to be recognized by telescopic observers? Limb darkening, the ever present dusty haze, and clouds also reduce the contrast of these features considerably. The extension of the atmospheric mass near the limb of the planet will also decrease the contrast of a surface feature. Numerous Martian craters have dark floors, so, how could a shadow of a crater wall be separated from the albedo of its floor? Telescope Resolution Theory Discussed
Initially, we use the Dawes criterion (4.56"/aperture) to define the resolving power of optical telescopes. However, planetary observers often use a higher resolving power than allowed by the Dawes limit for the threshold for planetary details. Dawes criterion only applies to resolving or "splitting" equally bright double stars and would not take into account the color, intensity, and contrast of the features on extended objects, or the effect of irradiation of bright objects that reduces the acuity of the eye.
Irradiation of bright objects, especially planets in the eyepiece, is evidently a physiological effect, originating in the eye itself and occurs between adjoining areas of unequal brightness. The extent to which the bright area appears to encroach upon the fainter one is approximately proportional to their intensity difference. Equally important is whether the targeted feature is darker or brighter than its background [Sidgwick, 1980].
Experiments by well known planetary observers conclude that they can see planetary details in excess of the Dawes criteria and this limit may be as much as 5 to 14 times too low. Some observers have claimed they can detect black lines on a light background in moderately bright lighting conditions well below the limit of resolution for their instrument; however, they do not say that they actually resolve the line [Buchroeder, 1984]. Pickering and Steavenson found by empirical means that they could see black dots on a white background from 2.3 to 3 times smaller than the Dawes limit [Dobbins et al, 1987].
Did John Mellish See Martian Craters From Earth?
Accounts from various sources, mainly from the Journal of the British Astronomical Association (Sheehan, 1994) and others, claim to have letters to and from John Mellish alleging that he had observed craters on Mars in November 1915 using the 40-inch Clark refractor at Yerkes Observatory in Williams Bay, WI (long. 88ºW 33.4’, 42ºN34.2’) during Central Standard Times (CST – UT = -6).
Complying with the Dawes limit a 40-inch telescope, such as that used by John Mellish in 1915 [Gordon, 1975], can resolve 0.114 seconds of arc. This yields only 31-km resolution of Mars' surface area when it is at 25.13 arcsec (largest apparent diameter). We can easily calculate this value by multiplying the diameter of Mars (6,792-km) by the image scale of the telescope: 6792 x 0.114 /25.13 = 30.8-Km. However, when Mars is only 7.7 seconds of arc, as it was during Mellish's observations in 1915, the resolution of the giant Yerkes refractor would be reduced to only 100-km of surface area. Even believing we can resolve 14 times better than Dawes criterion with this giant telescope, that leaves us limited to 7 kilometers resolution.
From various publications it is believed that John Mellish was observing Mars from 20 minutes to one hour before sunrise on November 13, 1915 and could have seen the crater Newton (154.5° – 161° W, 38.5° - 43.5° S) [Harris, 1995]. Let’s analyze this: The Sun rose at 1243UT (06:43CST) that day and Mars rose at 0444 UT (22:44 CST on 1915 Nov 12). That means that in order for Mellish to see and recognize the 6.5- degree wide crater Newton he would have to wait until the western wall of Crater Newton (161°W and 41°S) would appear on the southwest limb of Mars. Since the wall is at longitude ( ) = 161°W and latitude ( = 41°S, we find that the required Central Meridian (CM) to have to be 123.3°; mathematical proof: CM = / Cos - 90° = 161° / 0.75471 - 90° = 123.3°.
Running the program WinJUPOS we find the western extent of Crater Newton (161°W and 41°S) would not appear on the limb until 1504 UT (09:04 CST) when the CM was 123.3° and the Ds = 6.7 and Phase Angle ( i ) = 38.3°. So, the solar angle = CM + i = 123.3° + 38.3° = 161.6°. The shadow length ( S ) using the equation: h tan , where h = height of the object and , = shadow angle between the latitude
(1) and longitude (1) of the solar angle and the latitude (2) and longitude (2) of the object. To find , we will use the Spherical Law of Cosines, where 1 = 161.6°, 1 = 6.7°, 2 = 161°, 2 = -41°:
Cos ( ) = Cos(90° - 1 ) Cos(90° - 2 ) + sin(90° - 1 ) sin(90° - 2 ) Cos( 1 - 2 ) = Cos(90°- 6.7°) Cos(90° - (-41°)) + sin(90°- 6.7°) sin(90° - (-41°)) Cos(109.3° - 158°) = 0.116671 * -0.656059 + 0.993171 * 0.754710 * 0.999945 = 0.672972 = 47.7°
Hence: shadow length (S) = 2 tan 47.7° = 2.2 Km or 3 tan 47.7° = 3.3 Km
Therefore, a 2-km or 3-km high wall would produce a shadow of 2.2-km and 3.3-km respectively, only when the wall was positioned at the terminator and would decrease, as the wall is seen further away from the terminator. NOTE: A neat method to determine shadow length on Mars: "The Height of Lunar Mountains," at: http://www3.gettysburg.edu/~marschal/clea/clea_products/manuals/Lnmt_sm.pdf NOTE: The following images were produced by the “Save Image” function of WinJUPOS 9.0.0. and HST image STScI-PRC2007-45c.
The following table represents the longitudes of the evening terminator, the central meridians, and the morning limb for the times indicated:
Table II. A table showing the Universal Times (UT), altitude of Mars above the horizon, longitudes of the evening terminator on Mars, the central meridian , longitude of the morning limb of Mars and where the Sun points to at local Noon Mars time.
UT (CST) ALTº Sunrise ETº CMº MLº NOONº 0943(0343) 53 -3 344.0 35.7 125.7 74.0 1043(0443) 61 -2 358.6 50.3 140.3 88.6 1143(0543) 65 -1 13.2 64.9 154.9 103.2 1243(0643) 62 0 27.8 79.5 169.5 117.8 1343(0743) 55 +1 42.4 94.1 184.1 132.4 1443(0843) 46 +2 57.0 108.7 198.7 147.0 1543(0943) 35 +3 71.6 123.3 213.3 161.6
NOTE: ALT = altitude of Mars, CM = central meridian, i = phase angle, ET = evening terminator longitude before opposition: (CM – 90) + i, after opposition, morning terminator: (CM + 90) – i, ML = morning limb = CM + 90, EL = evening limb = CM- 90, NOON = Longitude of local Mars Noon hour before opposition: (CM + i), after opposition (CM - i). Observing +/- 3 hours of Sunrise, 1915-Nov-13.
Figure 3. LEFT: Mars on November 13, 1915 at 0943UT, RIGHT: November 13, 1915 at 1543UT [WinJUPOS 9.0.0 and HST STScI-PRC2007-45c]
Also, if we believe the same source, Mellish observed until 1526 UT (09:26 CST) [Harris, 1995]. Given a phase angle for Mars on that morning of 38.3 degrees and the CM for 1526 UT was 119.1°, we find that the longitude of the sub-Solar longitude (High Martian Noon) would be 118.7° + 38.3° or 157.0°. So, the crater Newton was on the same meridian as the Martian noonday sun -- very close to the south limb of Mars and the shadows would not have been seen extending out from its east-west rims. The only shadow would have been from the inside northern rim wall or possibly the outer south wall of the crater (see figure 3). Even if the center of Newton (158.3°W, 41°S) appeared on the limb at 1531 UT (CM 120.4°) only half of the crater would be visible and seeing such a feature that close to the southwesten limb is highly doubtful. Further evidence for these assertions can be found in the article, “Contra Gordon,” by Thomas A. Dobbins & William Sheehan.
Figure 4. Sequence of Mars Globes from 0943 UT until 1343 UT on November 13, 1915 [WinJUPOS 9.0.0 and HST STScI- PRC2007-45c]
Figure 5. Mars Globe from 1243 UT on November 13, 1915 [WinJUPOS 9.0.0 and HST STScI-PRC2007-45c]
Figure 6 Sequence of Mars Globes from 1343 UT until 1543 UT on November 13, 1915 [WinJUPOS 9.0.0 and HST STScI- PRC2007-45c]
NOTE: Two cataloged dust storms occurred in 1915 January 24-25 (206° Ls) in Phaethontis-Icaria and 1915 December 28-29 (037° Ls) in Aeolis-Elysium (Observatories Jarry-Desloges, Observationa des Surface Planetaires, Vol. 1-10 (1907-1941), Gauthier-Villars et Cie., Paris (1908-1946)).
Some even suggest Mellish identified Argyre Planitia (27° – 62° W, 45° - 61° S) as an impact crater; however, given the latitude of the feature and the De was 20° it is a stretch to even see this 5.8-Km (3.2-mile) deep feature clearly so far south on the southern limb of Mars. If Mellish began observing Mars at 1019UT (0419 CST) then the center of Argyre would be on the central meridian then and would have disappeared into the evening terminator 3.4 hours later at 1343UT (0743 CST). This author doubts anyone could have seen this shallow impression on Mars’ southern limb during early spring when the limbs are usually shrouded in a dense haze.
Figure 6. Argyre Crater on 1915-11-13-1020, CM 44.5°
One must also consider how “astronomical seeing” can decrease as the atmosphere begins to heat as the sun climbs into the morning sky. Often the best telescopic views of Mars can be seen well after sunrise; however, it is a stretch to say one has perfect seeing two or three hours after sunrise.
In a recent article in S&T the authors [Gordon and Sheehan, 2005] suggested that Mellish observed the crater Argyre around the time when the CM was at 79 degrees. That turns out to be at about 0641 a.m. local time, or at 1241 UT, on November 13, 1915 and at that time most of Argyre would be very close to or within the evening terminator. Given the southeast limb of Mars during southern autumn is typically hazy it is unlikely a shallow crater such as Argyre could have been seen that close to the limb of Mars.
Figure 6. LEFT: A shallow, low contrast topographic feature in the southern hemisphere of Mars; Argyre Planitia (27° – 62° W, 45° - 61° S) View of Argyre Basin, WinJUPOS V.11.0.0 13 November 1915 1241 UT. RIGHT: Animated image of Mars using WinJUPOS and mars-map.jpg [The Celestia Motherlode (CM): http://celestiamotherlode.net/creators/praesepe/MarsV3-Shaded-2k.jpgwithout atmospheric limb darkening, haze or clouds]
Furthermore, the source indicated that at least two more craters would have been on the illuminated disk of Mars during Mellish’s observing sessions; Copernicus (169° W, 49° S) and Kepler (219° W, 47° S). Copernicus is further southwest and closer to the south limb of Mars from Newton and would rise on the morning limb of Mars at 1223 UT (CM = 74.6°). The crater Kepler would not rise until 1605 UT or 3 hours and 22 minutes after Sun rise (CM = 128.6°).
An observer would most likely have great difficulty seeing topographic features on Mars that was so close to the south limb of the planet. Adding to the difficulty would be the clouds and hazes that are plentiful during the seasonal period (Northern Spring and Southern Autumn), therefore, surface features near the limbs would be more difficult to see through the typical morning hazes [Sheehan, 1992] [Sheehan, 1992].
The On-Line Atlas of Mars (http://ralphaeschliman.com/id30.htm) shows detailed locations for the following craters:
113-mile (182-Km) Green (8.5°W, 52.3°S) in the Noachis Quadrangle 497-mile (800-Km) Argyre Planitia (44°W, 50°S) in the Argyre Quadrangle 126-mile (182-Km) Lowell (81°W, 52°S) in the Argyre Quadrangle 185-mile (298-Km) Newton Crater (158°W, 41°S) in the Cimmeria Quadrangle 183-mile (294-Km) Copernicus Crater (169°W, 49°S) in the Cimmeria Quadrangle 145-mile (233-Km) Kepler Crater (219°W, 47°S) in the Prometheus Quadrangle
Figure 8 Globes comparing the 7.7 arcsec Mars on November 13, 1915 to the 13.9 ” Mars at closest approach on February 09, 1916 and the 25.13” Mars at closest approach on August 27, 2003.
A good time to test for those wishing to see craters on Mars from this planet may want to read this for details comparing 1915 apparition with the 2014 apparition.
Hubble Space Telescope (HST) Images
The one and only image of Mars available from the Hubble Space Telescope during the 2001 apparition reveals what may be considered identifiable craters. HST took the image around the time of opposition and it will be hard to deny the apparent resemblance between those crater-like appearances on this image of Mars and images of lunar craters. One caveat, however, is pointed out by Cornell's Jim Bell who wrote to Roger Sinnott in 2003:
"While I acknowledge that there can be moments of incredible clarity (some would even say clairvoyance) at the telescope, I have never seen any convincing evidence for the observation of craters on Mars based on their topography. It's not hard to be skeptical: the elevation differences are quite small and the phase angles are not ever really that large. However, I find it easy to believe that observers have seen craters on Mars in the past, not based on their topography but instead on their albedo variations.
A good example can be seen in the June 26, 2001 Hubble Space Telescope image, which is among the highest resolution images of Mars ever obtained from Earth. One can easily see a number of large and even smallish craters in the Meridiani and Arabia regions, but they are resolved because they are just shallow holes in the ground filled with dark sand scattered amidst a "sea" of bright dust. The craters in this area (and many others) are natural sinks for coarser-grained and thus darker particles, leading to these large albedo contrasts. Even the keenest observer could mistake the dark inter-crater deposits for shadows, especially for cases where the deposits fortuitously appear biased towards the direction that one might expect for shadows." [Bell, 2003].
Since the resolving power of a telescope can be degraded by poor optics and Earth's unsteady air we can eliminate these problems with the Hubble Space Telescope (HST) now that its optics have been corrected. Because the Hubble Space Telescope (HST) is located outside the Earth's atmosphere it might be considered the best instrument available for resolving planetary details. The aperture of the HST is 2.4- meters (94 inches), so, using the above theoretical limit for angular resolution the Wide-Field and Planetary Camera (f/30) would give 0.043 seconds of arc resolution [Beatty, 1985]. In August 2003 when Mars appeared to be 25.13 seconds of arc a telescope capable of resolving 0.043 arcsec would reveal a surface feature no smaller than 11.6-km.
Using the best known estimates of the average height of a Martian crater to be 3-Km [Strom, et al, 1992], and the stated resolution of HST as 0.043 arcsec arc [Beatty, 1985], then the largest surface feature on Mars to be resolved by HST would be 6,792.4 x 0.043 /20.49 = 14.25-Km. However, it is apparent that several craters can be identified on the June 13, 2001 image so we can then establish a new resolving power for the HST as: (20.49 * 3) / 6,792.4 or 0.0091 seconds of arc. If we then applied the resolving power to HST as 0.0091 seconds of arc to sloping wall of a Martian crater then we very well identify it as a crater at 4.73 times the Dawes limit of resolution.
The similarities between Lunar craters and the crater-like appearances are striking on the image below and several can be readily identified by comparing spacecraft derived maps and close up photographs to the HST image shown in Figure 9 (LEFT). Especially apparent is the crater Schiaparelli; a classical feature called "Edom," that displays telltale circular appearance with bright Sunlit and dark shadowed sloping walls. However, in another HST images taken during opposition in 2007 shown in Figure 9 (RIGHT) shows the same crater when Mars was 15.9 arcsec and the resolution is remarkably lower. The crater-like features shown on this image is not unlike those seen on CCD images of the Moon taken with a ground- based telescope.
Figure 9. The one and only CCD image of Mars taken with the Hubble Space Telescope for the 2001 apparition. LEFT: The apparent crater Schiaparelli may be seen and is labeled on the above HST image. RIGHT: Another HST image taken during the 2007 apparition shows the crater Schiaparelli with less resolution.
Summary
We will never know what John Mellish really saw on November 13th of 1915. No drawings, descriptions, or locations of craters he claimed to have seen have ever been presented by the proponents of his so-called observations have been made [Goodman, 1992] [ Dobbins, 2003]. In my opinion, John Mellish saw only what he imagined as craters on Mars. According to observing records of E.E. Barnard, seeing at the Yerkes Observatory during 13 - 15 November 1915 was less than good and it is doubtful Mellish found a few mystical periods of time when seeing was perfect. This article will not introduce any startling news and will not resolve all the debates that have gone on for years over the issue of what observers can see or not see. It will continue for years to come. However, it does point out some mildly interesting points that may help those who wish to evaluate images of Mars and to help those who tend to over process images to back off a little. We are again going through a period when observers feel they have little to contribute to the study of Mars and this is just not the case. The value of visual observing and drawing at the telescope is good training observers so that if they do engage in high-tech telescoping they will at least have a feel for what their images actually are supposed to represent.
From the time when man invaded Mars with spacecraft loaded with instruments we started hearing this complaint from observers that we were obsolete. During the 1978 apparition of Mars observers really began to lose interest in observing the Red Planet and the ALPO Mars Section only collected a few hundred observations from a few astronomers. With the encouragement and careful guidance of our mentor, Chick Capen, we began a long but steady recovery that peaked out during 1988 when we received from 320 astronomers over 7,200 observations by the end of that apparition. Drawings and other visual observations accounted for 41% of the total then and the reason we got more photographs and CCD images is quiet simple: it takes a lot more time to produce a drawing that it does to snap a photo. The ratio of visual observers to image takers was about fifty to one, with visual observers in the majority. Participation is also part of our game plan.
Some of the difficulties of observing topographic features on Mars are the limits in angular resolution of both the telescope and human eye. Also, the irradiation of this bright planet makes observing very difficult, especially without using proper filter techniques. Even using filters will not eliminate completely irradiation in the eye or reduce the effects of atmospheric diffusion enough to allow the surface of Mars to be seen as crisp and sharp as lunar details.
Mars has very little topographic relief and surface structures near the nighttime terminator are poorly lit. Transient albedo features also obscure shadows in red light, as hazes and clouds will do so in blue light. The contrast of surface albedo features would make it very difficult if not impossible to separate from shadows crossing onto dark surface material. From the first images sent back from Mariner 4 (15 July 1965), Mariner 9 (1971), and Viking 1 & 2 (1976-82), Mars has been shown to be a relatively low contrast planet and required extensive computer enhancement and processing to bring out surface details.
Mars' atmospheric diffusion, hazes, clouds, and dust obscures its surface to a great degree. Dusty veils will leave large regions of Martian topography obscured. Observers regularly report clouds and hazes over and around the Tharsis volcanoes as confirmed by spacecraft orbiters. Wind and possibly water erosion rendered Mars’ crater walls smooth and less contrasty as those on the Moon.
Also, we know from more recent observations that the giant volcanoes are seen as dark spots protruding from the dust vials that remain aloft after a dust event. It should be noted that at least one dust event occurred during early 1894 and one during 1915. Both events most likely occurred too far in advance of the observations made by Barnard or Mellish and would not have resulted in the same darkening of the volcanoes; however, if we assume that both observers did in fact see dark spots at or near the positions of the great volcanoes on Mars, we may also assume dust activity had occurred prior to the sightings. These assumptions have yet to be authenticated.
Optical quality and ambient conditions to produce sharp and crisp images are very important. Very few optical instruments are capable of resolving even to their theoretical limits. Rarely do we encounter conditions good enough to see much of anything on Mars even if we are lucky to be using a high quality telescope at that exact moment a particular mountain or crater is positioned where we want it to be. Often we make mistakes in measuring images and waste time trying to prove something that is not real.
After a youthful, weird sidebar college study of psychology I embarked upon another a study in human sensory -- while engaged in a totally different hobby from astronomy; however, surprisingly it came to apply to my understanding of telescopic observing. The study of Psychomotor Domain Taxonomy allowed me to adjust my habits while at the telescope enjoying Mars while avoiding illusionary visions of topographic relief that was already imprinted within my mind from books.
I found a most interesting web site: http://honolulu.hawaii.edu/intranet/committees/FacDevCom/guidebk/teachtip/domains.htm that defines Taxonomy much better than I could, so here it is:
“Cognitive Domain
The cognitive domain is knowledge or mind based. It has three practical instructional levels including fact, understanding, and application. The fact level is a single concept and uses verbs like define, identify, and list. The understanding level puts two or more concepts together. Typical verbs for this level include describe, compare and contrast. The application level puts two or more concepts together to form something new. Typical verbs at this level include explain, apply, and analyze. Delivery in this domain is typically a lecture/presentation and the evaluation will be subjective and objective test items.
Psychomotor Domain
The psychomotor domain is skill based. The student will produce a product. The three practical instructional levels include imitation, practice, and habit. The psychomotor domain is steeped in a demonstration delivery and the first level, imitation, will simply be a return of the demonstration under the watchful eye of the instructor. The practice level will be a proficiency building experience that may be conducted by the student without direct oversight of the instructor. The habit level is reached when the student can perform the skill in twice the time that it takes the instructor or an expert to perform. The delivery is demonstration and proficiency building in nature. The evaluation will be a performance or skill test. The content that is needed to be known to do the skill is cognitive and should be treated accordingly. If you are unable to choose between cognitive and psychomotor, ask yourself the following:
Is speed a factor?
Is equipment other than four walls of a classroom and an overhead projector necessary? Are you going to grade the activity in some way other than a paper/pencil test? If you answer "yes" to any one of these three questions, the learning domain should be psychomotor.
If you are still undecided and this is an occupational area, select psychomotor because that is the predominant occupational program domain.
Affective Domain
The affective domain is based upon behavioral aspects and may be labeled as beliefs. The three levels in the domain are awareness, distinction, and integration. The verbs for this domain are generally limited to words like display, exhibit, and accept and these apply at all levels. The first two levels are really cognitive; integration is behavioral and requires the learner to evaluate and synthesize. The content in this domain will usually involve discussions. The testing in the first two levels will be cognitive, whereas the third level will require an affective checklist.” Enjoy!
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