Observation Planetary Basics

Hints, Tips

Planets

Hints, Tips

Observations of solar system main bodies is one field of amateurs' activity. It's a very pleasant and rewarding observational activity

Planetary observation is always best done first naked-eye and pencil-drawing as drawing trains to perceive finer details. Most planetary observers associations make available observations forms which will train you about scientific observation. Planetary photography was deeply modified by digital tools. Some observers will prefer working on their own as some others will be happy to know that most observers' associations welcome observation submissions. Even observing for pleasure is very rewarding. Sky & Telescope/SkyTonight.com, the A.L.P.O. site, French S.A.F. site, are providing useful advices about planetary observing. Advices below -in the section 'Planets'- concerning the power and the instruments to be used as far as each planet is concerned, are given for advanced planetary observers and for visual observation only. Observing the planets with lesser instruments -or beginners' instruments- remains interesting in any case and some hints may also be given at each notice. The use of aperture reduction, which is available with some instruments like a reduced apeture in the cap at the telescope's top is a factor into reducing the too strong luminosity of main planets and allowing a better observation

Check How Planets are Rendered in An Instrument Function of the Best Power for A Given Apeture!
Check that useful diagram. It's showing how planets are seen into an astronomical instrument, function of the best power applied to a given aperture. The power is derived from the rule of thumb as described at the item 'Maximum Magnification Possible for an Instrument,' in the tutorial 'Some Usual Formulae for Instruments', as we multiplied, there, the aperture by a value number of 14. Planets, further, are seen as they are at they best, at the greatest elongation for an inferior planet, or at the opposition for a superior planet. note: that estimation of the rendering is based on a personal point of view, as any decision -like, for example, buying an instrument- should be based on using further sources of comparison (you may check, for example, at http://www.stelvision.com/ as they provide on their site a useful tool to represent astronomical objects rendering function of your instrument aperture in mm). click on the thumbnail!

Whatever the planet observed, some basics are useful like assessing the seeing or the transparency or having some fundamentals about celestial mechanics. The seeing is the turbulences due to the atmosphere and which may hinder the observation. The A.L.P.O. scale or the Antoniadi scale are used as assessment tools for the seeing. Transparency is what the lesser magnitude is seen at the time of the observation. With a fair weather and a anticyclon close to the observer's location, seeing conditions are good. Predictions are now available to amateur astronomers in terms of observations conditions generally as you will always get a advantage with cumulatively gathering data for you observing location function of winds, anticyclones and sky conditions. In terms of planetary observations, generally, the observer will have interest to observe any planet when passing your meridian -South that is- because a planet at that point, is at its highest in the sky and its light thus will cross less atmosphere and less prone to turbulence! Various methods allow that. Any observation has to make clear what part of the planet was observed. This is done through the "central meridian" that is the line from pole to pole which is seen at planet's center at the time of the observation. The value of such a data is given for Jupiter or Mars e.g. in magazines and at dedicated planetary amateur observation sites. On the other hand some basics about planets' apparent motion are useful, as are some additional data about planets visibility

Planets

Mercury Venus Mars Jupiter

Saturn Uranus, Neptune, and Pluto

Mercury

Power, instrument: 200x to 250x power are minimum; 100 mm instruments are a minimum as some phases may be reached through a 60 mm refractor. Physical data of importance: being an inferior planet, and nearest to Sun, Mercury appears only as a morning or an evening star. It is often low on horizon. This means poor atmosphere conditons. As Mercury is small and far, it displays a small apparent diameter. Features are subtle but may be seen however. Advanced observers may use filters. These are useful too against background sky glare. Miscellaneous: due to its slow rotation Mercury is the least mapped planet by space probes, and due to its proximity to Sun Hubble is never pointed to Mercury. Mercury appears in evening sky 12 days after its superior conjunction and in morning sky 5 days after its inferior conjunction. see a list of relief features names' meaning. see additional data about planets visibility

Venus

Venus is a quite difficult object for a small telescope. It is seen here with a 60-millimeter refractor picture site 'Amateur Astronomy'

Power, instrument: 6' (150 mm) for reflectors, 3' (75 mm) for refractors is a minimum. Venus is seen under a quarter shape when at greatest elongations as like a crescent some days before and after a inferior conjuntion. Venus endures high magnification. Physical data of importance: Venus features are elusive as they need a aperture of 150 mm like a minimum with a violet filter. Venus features observation is hindered by planet's strong brilliance. Planet is best observed against a clear sky (contrast with sky is not so important and does not hamper low contrast Venus features). Some observers track Venus too well into daylight in the evening or morning, and 20° above horizon seems a limit to avoid bad seeing. Observing Venus is always a trade-off between poor seeing (due to planet being too low), observation in too much daylight, and too much contrast between planet's brightness and dark sky. The largest crescent-shaped form of Venus is attained either by the beginning of a period when the planet is a morning star, or by the end when it is a evening one. The crescent is even accessible to 7x50 binoculars. Miscellaneous: Venus appears in evening sky 35 days after its superior conjunction and in morning sky 6 days after its inferior conjunction. A interesting fact about Venus is that it can be spotted in the afternoon daylight, should you know exactly where to look, and if you can focus your eyes on it. The sight is helped, for example, when a Moon crescent is hinting to where Venus lies, and giving your eyes something to focus on. Blocking the light of the Sun through some obstacle is also helping. Modern astronomical software are helpful to tell you where Venus is. Venus then is seen like a tiny brilliant pinpoint of light. It is remarkable that such a sight occurred at the occasion of the inauguration of Abraham Lincoln for his second term as U.S. president, about possibly near 1 p.m. with a peculiarly clear condition of the atmosphere. During such a observation, ALWAYS CAREFULLY WATCH not to gaze at the Sun naked-eye or with binoculars, a telescope or a whatever photographic device! see a list of relief features names' meaning. see additional data about planets visibility

Mars

Mars keeps a distant object in a beginner's telescope! Mars is seen here at the 2013-2014 opposition with a 60-millimeter refractor picture site 'Amateur Astronomy'

Power, instrument: a 200x magnification is a minimum, 100 mm of aperture for refractors, 150 for reflectors are minimum. Some source however state that even a small, 60-mm refractor with a 70-100 magnification, is enough to show the polar caps and some dark surface features at the time of a opposition! Filters are of use in Mars' observation. A yellow (W-15) filter is of use with smaller telescopes from 3 to 6 inches as CCD cameras are usefully equiped with filters designed to the camera's spectral response. Physical data of importance: seasons are about twice Earth's seasons and day is slightly longer. Mars except near opposition always shows a gibbous phase. Features drift significantly in one hour or two. Each pole is capped by a polar cap which retreats in the hemisphere's spring and winter. Each cap, until local spring is overheaded by a thick cloud (termed the "North (or South) Polar Hood". Albedo features (the dark terrain regions) endure seasonal and secular changes. Miscellaneous: many observers use color filters. Mars is a fine object to observe. The difference of albedo in the martian terrains are due to that some are reflecting less light and look darker, and some are reflecting more light, looking brigther. The southern hemisphere at Mars is mostly ancient cratered highlands and dark terrains, as the northern hemisphere features younger and brighter plains. Observing Mars is largely spotting the Martian regions and to study their possible changes along the cycle of the seasons. More accurate centers of interest may be dust storms, or clouds. Syrtis Major Planitia was one of the first features identified on the surface of the Red Planet by seventeenth-century observers as Christiaan Huygens used this feature to measure the rotation rate of Mars. Astronomers eventually determined that Syrtis Major is a ancient, inactive shield volcano. Hellas Planitia basin is about 1,100 miles across and nearly five miles deep, and formed about 3.5 billion years ago by a asteroid impact. Arabia Terra, a vast upland region in northern Mars that covers about 2,800 miles, is densely cratered and heavily eroded, indicating that it could be among the oldest terrains on the planet. Dried river canyons (too small to be seen) wind through the region and empty into the large northern lowlands. Sinus Sabaeus and Sinus Meridiani are darker regions covered by dark bedrock and fine-grained sand deposits ground down from ancient lava flows and other volcanic features. Such sand grains are coarser and less reflective than the fine dust that gives the brighter regions of Mars their ruddy appearance. Early Mars watchers first mapped these regions. East of Syrtis Major you will find the large dark lane of Mare Tyrrhenum and Mare Cimmerium. The opposite hemisphere of Mars is vast and light, with Tharsis, Amazonis or Memnonia, and, full South, Mare Sirenum. An interesting intermediate region is about Chryse Planitia with, South, the vast dark zone of Solis Lacus. Mars' both moons are Phobos (with the 11th magnitude) and Deimos (with the 12th) as they are orbiting close to their planet. see a list of relief features names' meaning. see additional data about planets visibility

click to a map of Mars. ckeck the same map in black-and-white. map site 'Amateur Astronomy' based on material courtesy NASA/JPL/Malin Space Science Systems

Jupiter

Jupiter is a easy object to amateur astronomers! Jupiter is seen here imaged through a astro webcam with a small refractor! picture site 'Amateur Astronomy'

Power, instrument: Jupiter typically is a easy planet, already accessible beginning with a power of 45x and the ballet of Jupiter's moons too. The ideal is with a 200-300 mm telescope at a 200-300x magnification. The main trouble in terms of observing Jupiter is the planet's swift rotation. Some source state that the GRS is available beginning with a 100-mm reflector only because it does not feature contrast enough and the same for a satellite's shadow but, in that case, for cause of not enough resolution. Moons are accessed already with binoculars, at least to the most luminous of those. Physical data of importance: Jupiter, is characterized by a series of bands, zones and belts, parallel to the equator, nomenclature of which is to be used in observation reports. "Great Red Spot" (GRS) is a cyclone twice Earth's size. It exists since at least one century and is located South of Jupiter' equator

click to a chart of Jupiter nomenclature (belts, zones) (left), to a chart of Jupiter nomenclature, smaller format (right) see a detailed list of belts and zones. South is up. pictures © site 'Amateur Astronomy' with a picture Cassini-Huygens mission

Jupiter's storms are dynamic. Confirmed observations of the Great Red Spot date back in 1831 as a continuous record of at least one observation a year dates back to 1878 a date when the Great Red Spot began to shrink with some growth along the way. The Great Red Spot recently started to drift westward faster than before as jet streams to the North and South hold it at the same latitude. The Great Red Spot’s color has been deepening, too, becoming intensely orange since 2014. Jupiter's Great Red Spot clouds race counterclockwise around the oval's perimeter with wind speeds greater than any storm on Earth. The Great Red Spot's core, which typically has a more intense color, is less distinct than it used to be as aunusual wispy filament is seen, spanning almost the entire width of the vortex (the question whether it is accessible to amateurs is pending). A large, transient storm called the 'South Equatorial Disturbance,' (SED) is also blowing in the southern hemisphere of Jupiter as it is seen like a dent into the band into which the GRS is to be found. Massive counterclockwise rotating storms, in a number which varied from 6 to 9, exist as white ovals in the southern hemisphere since 1986. Satellites are also part of the show: they may transit in front of planet disk, be eclipsed by Jupiter's shadow or themselves cast shadows (like Moon is doing at Earth during a solar eclipse) on Jupiter. Double eclipses are relatively frequent and may occur in a row. Triple eclipses occur each decade, as quadruple eclipses never occur. As far as mutual phenomenons of Jupiter's Galileans are concerned, check with additional data about planets visibility. Miscellaneous: Jupiter possesses three longitude systems (I, for visible equatorial features, II for visible mid-latitude to polar features, III for radio and professionals). Satellites magnitudes range for 5.1 for Ganymede to 6.2 for Callisto (Io is 5.5 and Europa 6.1). Due to an important apparent diameter, Jupiter is an easy target for amateurs. Recently a 'Red Spot Jr. has appeared as the Great Red Spot is bumping against that other storm. Since early 2010, Jupiter too lost his southern equatorial band, a occurrence which might be cyclical as the SEB belt reappeared 10 months later. see additional data about planets visibility

Saturn

Power, instrument: ideal are a 6' (152mm) refractor or a 10' reflector as the absence of turbulence is the main factor with small telescopes. The Cassini division is accessible through a 100mm telescope only. Physical data of importance: Saturn, which shines sedate yellowish glow, is characterized like Jupiter by a series of zones and belts parallel to equator; features are less impressive than Jupiter's. Rings are an object of observation too, as may be Saturn's satellites. During most of Saturn's lengthy year, the projection of the planet's shadow extends well beyond the edge of the A ring, as at the time of the summer solstice, the Sun is higher in Saturn's sky, freeing most of the A ring from the shadow. Miscellaneous: two system of longitude are used (I -equatorial regions, II -north or south of previous). Zones and belts are given a specific nomenclature like for Jupiter. Saturn's ring is included in the nomenclature too. Satellites magnitudes are ranging like: Titan 8.4; Rhea 9.7; Tethys 10.3; Dione 10.4; Enceladus 11.8; Iapetus 10.1-11.9; Mimas 12.9. see additional data about planets visibility

click to a chart of Saturn nomenclature (belts, zones) (left), to ring features (center), to nomenclature-ring smaller format (right). South is up. see a detailed list of belts and zones. pictures © site 'Amateur Astronomy'

Uranus, Neptune, and Pluto

Power, instrument: -na-. Physical data of importance: Uranus, Neptune and Pluto are faraway worlds and all nead important apertures to be observed. Miscellaneous: Uranus axis is tilted on orbit beyond orbit's plane (97.8°) as it presents us either its northern or southern hemisphere. After one of its equinoxes which occurred in 2007, Uranus is now amidst its northern hemisphere summer and a bright, large stormy cloud cap settled at the pole. Last solstice (we were seeing southern part of the planet) took place in 1985, next one (we will see planet's northern part of the planet) will be in 2030. The faraway world is seen like a disk as soon as with a 60-mm refractor. Titania and Oberon, Uranus' moons may be glimpsed with apertures as small as 8" as Umbriel and Ariel are much more difficult to observe. Atmospheric methane at Uranus and Neptune absorbs red light but allows blue-green light to be scattered back into space, giving each planet a cyan hue. Neptune: it is seen like a disk at 100x in a 100-mm telescope. Immense dark storms on Neptune were first discovered in the late 1980s by NASA’s Voyager 2 spacecraft but such elusive features are playing a game of peek-a-boo over the years. Hubble found two dark storms that appeared in the mid-1990s and then vanished. A latest storm was first seen in 2015, but is now shrinking. Neptune’s dark vortices only last a few years. Neptune is about midway its aphelion (which was in July 1959) and its perihelion. It will reach the latter on Oct 9 2042 only. Pluto: it is seen like a pale star of the 14th magnitude in a telescope with a 250-300mm aperture; due to its orbit, Pluto is orbiting inside Neptune's orbit during 20 years; this last happened between 1979 and 1999. Next time Pluto will come back inside Neptune's orbit will be on April, 5th, 2231 only. The faraway world never exceed the 14.3th magnitude, which necessitate a telescope with a 12-inch aperture. see additional data about planets visibility