🙎🏾 🆚 🃏 How to observe the moon and planets 🐝 😌 🤰🏿

Observing the moon and planets is very interesting. Observation of the planets is not prevented by light exposure and they can be observed directly from the city. To observe the planets, eyepieces with a large field of view are not required. Even inexpensive Plessla eyepieces can provide a productive visual observation result.

Jupiter, Saturn and Mars are perhaps the most accessible planets for astronomical observations. I still remember the thrill and surprise of the first glance at Saturn, which I saw more than 20 years ago, in the 80mm Big School Refractor. However, there are often reports from beginner amateurs about the first observations, in particular of Jupiter and Mars, in which there is some disappointment. "I just see a ball of light without details," or "I see a small disk that I can’t fully focus on." “Is my telescope defective?” It is the day of novice astronomy lovers that this article may be useful. It describes in detail the subtleties and features of visual observations of the planets of the solar system.

Planets are points of light in the sky, but the moon is large and very bright. However, the Moon has many smallest details, so for their consideration it is necessary to use the same techniques that are used to observe the planets. There are several important factors to consider in order to get the best image with your telescope:

Increase
Resolution
Shine
Light scattering
Contrast
Sharpness

Increase

The most controversial factor. The planets are small, so the larger the increase, the better !? Not really. You need to use the optimal magnification for your telescope. The easiest way to find it is to calculate the optimal exit pupil of the telescope. The exit pupil is the size of the focused image that you see through the eyepiece in your telescope.

The exit pupil is calculated as follows: the diameter of the lens in the telescope in mm, divide by the magnification given with one or another eyepiece. Let me remind you that the magnification of the telescope is calculated by dividing the focal length of the lens in mm by the focal length of the eyepiece used, also in mm.

The focal ratio (F / D) of the telescope lens is calculated as follows: divide the focal length of the lens by its diameter (aperture)

It turns out that for the human eye, a 1 mm exit pupil provides the best resolution for well-lit objects. Let's say you have a 90 mm refractor with a focal length of 900 mm and a focal ratio of F / D-10. In this case, to get the best views of the moon or planets, you must use a 10 mm eyepiece. For F / D-5, use a 5 mm eyepiece, for F / D-8, an 8 mm eyepiece, and so on. Using this increase, most of the nights you can enjoy a beautiful view of the planets.

There are two exceptions:

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Resolution depends on two factors: the diameter of the telescope lens (the larger the better) and visibility. Visibility (sing) is a measure of atmospheric stability. If it is stable, you will see more details; if there is a lot of turbulence in the atmosphere, then small details will be “washed out”. If visibility is poor, a 10-inch telescope will not show you more than 4-inch. In fact, small tools do a little better with a bad atmosphere. Also, making observations as high as possible from the surface of the earth and away from heat sources (for example, roofs) will help reduce the negative effect of “image streaming”. In Soviet literature, it is recommended to climb at least 300m. from sea level, to the tops of hills, piedmont plateaus, etc., to exclude a negative effect on the image of the surface thermal layer. But you need to knowthat the peaks of freestanding hills would be poor choices due to air turbulence.

The moon and most planets are very bright. Often the smallest details are lost under intense illumination of the eyepiece, a bright spot that builds the lens in its focal plane. How to control it? The easiest way is to create light pollution. Night adaptation of the eyes is counterproductive when it comes to observing the moon and planets. Turn on the lights on the porch, balcony or any other place where you are observing. Better yet, watch when the sky is still blue. The best views of Jupiter I had right before sunset. If this is not enough, you can either use the aperture in front of the lens (especially recommended on the Moon, in the absence of a specialized filter), or use filters. The aperture setting is quite effective for fast telescopes, with a focal ratio F / D-4 ... F / D-6.For less aperture instruments with a smaller aperture, such as: F / D-8 ... F / D-15, I do not recommend this, as this reduces the resolution. Filters will be more effective (more on choosing a filter later).

Light scattering

Light scattering occurs when the bright light of the moon, planets or stars hits the glass surface of your telescope. Scattering effects are similar to glare, loss of contrast and resolution. Unfortunately, you cannot control the scattering of light with filters. The only way to deal with this is to choose a diagonal, Barlow, eyepieces and filters with good control of the level of light scattering. Simply put, of good quality, I recommend choosing a diagonal with a dielectric coating on the mirror surface.

Contrast

The purpose of observing planets and the moon is to provide high contrast. This is achieved by controlling glare and light scattering, as well as selecting eyepieces with good contrast. You can also improve the contrast of some of the details of the surface of the moon and planets using the appropriate filters (more on this below). Also, when applying large magnifications, you can notice a decrease in contrast.

Sharpness

Some optical telescopes are capable of building a sharper image than others. Suppose you probably already have a telescope, in which case it’s better to focus on a conscious choice of Barlow’s eyepieces and lenses. Many eyepiece models produce a “blurred” picture at high magnifications. Unfortunately, some of them are sold as planetary eyepieces. Orthoscopic eyepieces - are the best eyepieces for observing planets. Budget eyepieces can also degrade image sharpness.

Recommendations for choosing a telescope and accessories for it:

Telescope

In the vein of planetary observations, you can use any telescope, regardless of size and optical design. However, if you make a purchase specifically for observing the Moon / planets, telephoto instruments with an F / D-8 ... F / D-15 ratio will give better results. A design without chromatic aberration is preferred since XA reduces resolution, especially when applying large magnifications.

In terms of performance, we can recommend:

80-120mm long-focus achromatic refractors and small 80-100mm APO / ED refractors.

Catadioptric telescopes (Maksutov, Schmidt-Cassegrain) with a diameter of 5-11 inches can also be recommended. But to use their potential, unfortunately, will not succeed often, due to the instability of the atmosphere.

Larger APO refractors are capable of producing high-quality, large increases, but they are expensive. Newton's large telescopes and catadioptrics can potentially provide the best views of the planets. However, in order to take advantage of a larger aperture (lens diameter), in order to obtain a higher resolution, it is necessary to choose nights with exceptional atmospheric stability. This does not happen very often, and on an average night using a smaller lens diameter will be more practical.

Filters

Filters should be your next priority after a telescope, and they should be of good quality. Stay away from modern planetary plastic filters sold by many manufacturers. They degrade resolution and increase light scattering. For purchase, I recommend Baader, Lumicon or Refinery glass filters. You can search for used on ebay, astro flea markets, etc., the main thing is that the filters are not scratched.

Neutral density and polarizing filters are often recommended for the moon and planets. I used them at the beginning, but I realized that color filters give better results.

Color filters not only reduce glare, but also improve the contrast of surface details. Orange No. 21 is the best filter for the crescent moon and for Saturn, it also works well on Mars. The best filters for Mars are red No. 23A and for large apertures - red No. 25. Blue No. 80A is suitable for Venus and Mercury, and green No. 58 is suitable for the full moon. Jupiter was the most difficult in terms of selecting the best filter. Over the years I have tried many filters. Among the color filters, only blue No. 80A came to my aid.

There are a couple of special filters from Baader that I highly recommend for Jupiter, Saturn, and Mars (although they are too weak for the Moon, Venus, and Mercury). Baader Moon and Sky Glow is the best filter for Jupiter, much better than blue No. 80A. For Saturn and Mars, you can get the best results with the Baader Contrast Booster contrast filter. When the planets are very bright (near the confrontation), you can use two filters: Baader Moon and Sky Glow and Baader Contrast Booster together and use them for all three planets. What I especially like about these filters is that they reduce glare and enhance contrast, but do not significantly alter the natural colors of the surface of the planets.

Eyepieces

Orthoscopes! No matter what your increase is the most working, I strongly recommend that you purchase at least one of them for the planets. Orthoscopic eyepieces combine sharpness, high contrast and excellent reduction in light scattering. Used orthoscopes can easily be found in the $ 40-60 range. Most of them are produced at one or two plants in Japan, so quality control is usually good. If you prefer to buy new ones, then the best value for money is Baader Classic Orthos (BCO). BCOs also have a 50-degree field of view, which is much larger than conventional orthoscopic eyepieces, as well as Plessla eyepieces.

Two limitations of the orthoscopic scheme are a narrow field of view (40-50 degrees) and a short pupil extension at small focal lengths. For example, an 18-mm orthoscopic eyepiece has a convenient pupil projection of ~ 14 mm. When used with 2x Barlow, the effective focal length becomes 9 mm (used in telescopes with focal ratios F / D-8 ... F / D-10. When using 3x Barlow, the effective focal length becomes 6 mm (used in telescopes with focal ratios F / D-5 ... F / D-7).

Over the years I have tried many eyepieces, in the price range from the initial to the middle level. Some of them have a blurry image at high magnifications, low contrast and terrible scattering of light. Orthoscopes are the best solution for planets. However, if you prefer a wider field of view (especially relevant for owners of the Newton telescope, on a Dobson mount, without the ability to guide the object with micrometer screws) or a large pupil extension, you can recommend Vixen SLV, TeleVue Radians and Delites, Explore Scientific 68 and 82 series and Meade 5000 UWAs as high-quality Moon / planetary eyepieces. With a very limited budget, you can get by with Plessla eyepieces, but you just need to take quality ones.

Someone would say: “My eyepieces work fine on the moon,” so it is. The moon is a very easy object to observe. If your eyepiece builds a slightly blurry image, you will still see a lot of detail. Nevertheless, testing sharp, top-end and very budgetary eyepieces next to each other will be a revelation. Like switching from good analogue television to HD broadcasting, the difference is very expressive

Barlow Lenses

You do not need Barlow if you have eyepieces in the right range of focal lengths. In addition, Barlow budget lenses can degrade contrast and increase light scattering. However, good, quality Barlows may be helpful. To get 1 mm or less of the exit pupil in a short-focus telescope, you need to use an eyepiece with a short focal length. In this case, the removal of the pupil may be uncomfortable. The best option, in this case, may be to use a 2x or 3x Barlow, together with a longer telephoto eyepiece. In addition, Barlow increases the effective focal length of the telescope, as a result of which it is possible to obtain better planetary images with a combination of the Barlow lens + eyepiece, compared with a short-focus eyepiece. Baader Q barlow 2 can be highly recommended.25x barlow, and in the premium segment TeleVue 2x and 3x barlow.

Diagonal

The often overlooked part in the optical path is the diagonal. It can be the cause of less “stellar views in the telescope’s eyepiece." One of the main priorities should be to increase the diameter of the diagonal. If the telescope has a 2-inch focuser, it is advisable to switch to a 2-inch dielectric diagonal, which will improve the image for both DSO (Deep-Sky objects) and planets. I have had good experience with the mid-priced, dielectric diagonal from GSO. You can also recommend manufacturers: Celestron, Orion, Explore Scientific.

If you are looking for the best diagonal for the moon and planets, I would choose a prism of good quality. Prisms scatter less light than dielectric mirror diagonals and are more preferred for the moon and planets. In terms of performance to price ratio, I would recommend the Baader T2 prism.

Observation

Moon

On the moon, most of the details are visible on the border of the illuminated and unlit surface of our companion. Since the terminator (the line along the border of day and night) changes its location every day along with the moon phase, you can enjoy new views every night. Even with the smallest telescopes and binoculars, you can see many craters on the surface of the moon. A larger aperture allows for finer details. With my 8-inch Schmidt-Cassegrain telescope, on average per night, I can figure out the details up to ~ 1 km and spend the entire observation session in one crater, studying the complex shapes of walls, a central slide, microcraters and other minute details.

Mercury and Venus

These planets are not visible for months. For only a short period of time, they are observed as a “morning or evening star”. Mercury is more difficult to detect, since even at periods of distance from the Sun, it is still located pretty close to our star. The search for Mercury with the naked eye is already an achievement. On rare days, coinciding with the elongation of Mercury (maximum distance from the Sun), with a calm, clear atmosphere, the planet can be seen near the horizon. The phase of Mercury can be seen even in small instruments.

Venus is easier to see. The elongations of the planet last for weeks. Even the most modest binoculars (such as 10x50) can show the phases of Venus. In large telescopes, using filters, it is sometimes possible to resolve darker clouds in the atmosphere of Venus.

Mars

During the year, Mars moves rather quickly through the zodiac constellations. If it is in the sky, most of the time you can see only a small orange disk of the planet, without any details. However, once every two years, Mars comes into opposition (confrontation with the Sun), when its apparent dimensions increase significantly. The next opposition will take place on October 13, 2020, so get ready! :) You can start observing the planet from July!

Mars is the most difficult planet to observe due to the low contrast of surface details. Filters and eyepieces must be good. But even with an 80 mm telescope and patience, during the confrontation, you can understand many details on its surface. The focus of the observation is that you do not have to rush, keep the planet in the field of view of the telescope and wait for the moment when the details of the surface "draw out" more clearly, at the moments of calming the atmosphere. This, by the way, is a general strategy for observing such planets as: Jupiter, Mars and Saturn.

Jupiter

Jupiter is usually visible for 4-5 months, every year. Thanks to the dynamic quartet of its satellites and its rich details, Jupiter is one of the most interesting objects in astronomy. Even binoculars with a 10x50 optical design allow the disk of the planet and its 4 satellites. Using large magnifications and the diameter of binocular lenses (for example 15x70, 20x80), you can easily see a couple of main bands on its disk. When observing using high-quality filters and eyepieces, even with an 80 mm telescope, it becomes possible to see the complex system of Jupiter's bands. You can also observe the transits of the Great Red Spot and the shadows of the moons of Jupiter, across the disk of the planet. Increasing the diameter of the telescope to 8 inches or more, will increase the color saturation of Jupiter,show more small details in the belts and polar regions of the gas giant (including small storms and festoons). It will also allow satellites on small disks. Watching Jupiter is a great skill, with practice you will learn to see more.

Saturn

Like Jupiter, Saturn is visible for 4-5 months every year. But unlike Jupiter, its apparent size is smaller. With binoculars 10x50 looks like an egg, with some practice and sharp optics, with binoculars 15x70, tiny rings can be resolved around the disc. Rings are easily detectable even in modest telescopes. A relatively small increase in aperture will show the “Cassini gap” in its rings (no filters are required). Saturn's cloud system has a much lower contrast compared to Jupiter. To resolve the details on the planet disk and in its rings, filters and an increase in the diameter of the telescope objective are necessary. The largest satellite of Saturn - Titan, is clearly visible even at low magnifications. With a large telescope, several more satellites can be resolved.

Uranus and Neptune

They tend to remain in the same constellation for many years. Autumn is the best time to observe them, for the past few years. Both planets can be seen in the form of "blue stars" with binoculars or in a small telescope. Using an 8 inch or larger instrument, one can see very small, greenish planet disks, with no surface details. Also, using large telescopes (from 8 inches and above), you can see Triton, the satellite of Neptune, and at least three satellites of Uranus.

Pluto

Still a planet in my perception! :) He is in Sagittarius, the last few years. In a very stable atmosphere, it can only be seen as a very faint star, using a telescope with a diameter of 8 inches or more.

"Parade of planets"

Every two or three years the planets line up, and they are visible all at once, in one night. I have observed this phenomenon in the past - very impressive! :) Next time I will report this phenomenon in advance.

Unfortunately, I could not describe all the nuances of observing the moon and planets in one short article. I hope I have provided enough information to interest you in planetary observations. I hope this article will be useful to someone.

Ask if you have questions, feel free!

All clear skies and exciting observations!

The group’s editor-in-chief at Open Astronomy VK, Konstantin Radchenko.
Our group: vk.com/openastronomy

How to observe the moon and planets