The Art of Observing Part 1- bright objects [Mars updated 8/24/03]
Jul 19 '03 (Updated Aug 26 '03)
The Bottom Line Astronomy is one of the few adventures you can have from your back yard.
I first wrote a review on choosing a telescope based on my own lifetime experience and the small forest of tubes sharing my home. Since then, I have known quite a few other people moving into the hobby, and our collective experience has revealed a lot of issues to me which weren't so obvious previously. I am writing this to address the common experiences a beginner faces. This review will include basic descriptions of some objects as they appear to the naked eye.
First, I have learned people really love telescopes and getting to see things for themselves. A telescope in the driveway at dusk is a neighborhood magnet. However, observing is a bit of an art. Knowing a few tricks will help, and also knowing what it is you are seeing helps a great deal as well.
Everyone who can see the moon wonders what can be seen or not. And, of course, everyone is bombarded with Hubble telescope photos showing amazing views of galaxies, planets and nebulas with incredible colors.
Actual images are at the same time more and less than what people often expect, and this results in some confusion for many new observers.
Here is a list of several objects and some information on what different kinds of views will look like.
The Moon
The moon is the one night sky object everyone can find, and the only one you can see in daylight as well. NASA completely surveyed the moon during the Apollo program back in the early 1960s, but it has since dropped out of popular print, and many moon maps are strangely unrevealing. There is an undiscovered country in the moon for us all.
The area of the moon's disk is approximately the area of the continental United States. As a result, the features you see are often the size of entire states. It is covered with mountains, valleys, craters, lava fields, and other features visible from earth. the best time to view the moon is as it is changing phases. As the moon goes from being a thin crescent to a full moon, each night a new area has sunlight shining across to put the features in sharp relief with fantastic contrast. Because of this, the moon is a real crowd pleaser.
Now, what you will discover is no matter what telescope you are using, there is an urge to zoom in further and further as more details are hinted at, and finer and finer details will become visible in larger telescopes. The main problem is atmospheric conditions will ultimately win out. This is an unfortunate fact of life. On the other hand, you do get to see a new area of the moon in relief each night, and the variety of features is amazing. Even low power views where the whole disk of the moon is visible are impressive in a telescope as the magnification brings craters and mountains into visibility, and the dark areas of the moon become visible against the night as they are lit by light-blue light reflected from earth (called "Earthshine").
The other unusual feature of the moon is photographs never seem to really do it justice. The huge amount of contrast from bright light to pitch black available to your eye is much more potent than what print on paper or an image on a computer or television display can achieve.
Now, the other item people always ask about is being able to see the Apollo landing sites. You won't be able to see them. No telescope on earth ever has. Hubble doesn't have enough resolution to pick them out. The reason is even at high magnification you are looking for an object the size of a car on a field of view encompasing an area the size of Texas. The only time an Apollo landing site was sucessfully photographed remotely was by one of the Apollo command modules in orbit around the moon, where the range was far less.
Planets
Planets are, hands down, my favorite objects in the sky. I look forward to when Jupiter and Saturn are in the night sky each year and will make a point of visiting them both any night they are in the sky. I am dividing this section up into what the different planets look like and what they do over time.
Mercury: This planet is closest to the Sun, so it is never very far from the horizon at sunrise or sunset. Unlike Venus, Mercury is almost never easily visible for most people. This planet is a rocky ball, and many observers only seriously look for it when it is coming between the earth and the sun, so its disk is seen as a sillouette when viewed by a telescope with a special filter over its front end. It is sometimes possible to see phases on Mercury, where it is a small crescent, but since it is low to the horizon, you will need to be somewhere with clear calm air for this to be visible.
Venus: After the moon, Venus is the brightest natural object in the night sky. It has a year shorter than earth's, and is only slightly smaller than earth. Since it is also inside of earth's orbit, it is also only visible before dawn and at dusk. This planet is therefore known as both the morning star and the evening star. At times, this planet will be seen close to the moon and other objects and produce beautiful scenes in the sky. It appears pure white thanks to a cloud cover of sulfuric acid droplets. Its surface is hot enough to melt lead and instead of venting heat like the earth does via plate tectonics and volcanoes, Venus periodically splits its entire crust which then sinks into molten rock which cools to form a new surface. With this happening every few hudred million years, we can be reasonably sure this planet was never a home for life.
That said, Venus is beautiful in the sky. If you zoom in with a telescope, you will see it go through phases like the moon as it goes around the sun. No other features are visible, and Venus has no moons, so I generally don't spend a lot of time on it. Venus is otherwise noteworthy because it is so bright it is frequently confused for aircraft or UFOs.
Mars: First of all, Mars gets a lot of misleading press. It is a little different than what you would expect. Unlike Venus, Mars isn't a life-size simulation of hell, but is instead a frozen ball with a thin atmosphere. Mars has a 25 hour day, so it will slowly show you new features as you look at it. This planet has very little atmosphere- one half of 1% of what we feel at sea level- exposure to pressure this low would kill you in seconds. The atmosphere it does have is 98% C02, so even if you could withstand the pressure, the 20% oxygen 80% nitrogen atmosphere we breath on earth is missing. To top that off, the temperatures are cold enough to turn that C02 into dry-ice snow every winter. And yet, there is a concept this is a "Haven" for life, even though it is more like Antarctica with a near vacuum of poisonous gas.
Even so, people love Mars, and I, with millions of other people, will be watching as it makes its closest pass to earth in 60,000 years on August 27, 2003. What you should know is Mars is an extremely difficult observing object. The planet is smaller than earth, so even at its close approach, it will only appear to be half the size of Jupiter. Looking for features on Mars is a little like looking for features inside a small-sized crater on the moon.
The color isn't all that red, and the contrast is very different from photos. The color is more of a "Peach" color than anything. If you are familar with clay soils in the southeastern US or the red rocks in the Southwest, both of these are more red than Mars. Mars rises around 11:00 now and will rise a little earlier each night. The color is quite obvious without a telescope, so please feel free to draw your own interpretation. The 1997 Pathfinder probe photos were a fairly accurate color depiction. In the 1970s, it seems someone at NASA said "Mars should be red! Make the photos Red!" and so the saturation was pushed on the released images (people who worked on the 1997 mission have commented on this).
The planet itself has very different contrast than you may expect. The disk will be obvious, but the colors are much closer to each other than you may expect. Even when in perfect focus, you will find yourself working very hard to make out the polar cap for the first time, when it looks white on ochre in photographs. Getting a view from a really large telescope helps get oriented for the first time. After the features become apparent, it gets easier. As of August 8, the polar cap is very easy to make out and the dark areas on the planet show up fairly easily. The color is nice and clear, but it will take a new observer a little bit to get used to the contrast. I will see about posting some of my photos so you can get an idea. I haven't had a night with seeing clear enough to make out fine detail, so I will have my fingers crossed for rest of this approach. As it is, the planet is already larger than in 2001, so go ahead and start looking.
As of August 17, Mars has started to get very interesting. In viewing on the early morning of Saturday, the 16th, Mars has obviously become larger and its appearance is changing. The South polar cap has very clearly receeded in the past week. It looks like it doesn't take long for the frost to evaporate. The dark areas are more apparent than ever, but the main problem is the seeing still hasn't been very clear. To say the least, this is a bit frustrating- but then again, I wasn't tying to be funny when I said Mars is hard. The local astronomy club, the Ponchartrain Astronomy Society, is sponsoring an event at the Kenner Science Center, just west of New Orleans, and several of us are planning on bringing all the observing gear we can muster if it isn't actually raining.
As of August 24, Mars has a slightly smaller polar cap than before. The most noticable difference is other details on the planet are becoming visible. The planet is extremely bright to the naked eye, now, and a mid-sized telescope will show the disk and polar cap as being completely obvious now that the planet is so unusually close. The subtle shading of other features is much more apparent along with the texture of the planet's terrain. It is very beautiful, but like looking at a full moon with your naked eye, you get the feeling you can almost make out something more, but not quite. I really need to get a space photo server set up, though- I have photos from different scopes which are very informative.
Mars has weather, seasonal color changes, volcanoes, and canyons to look for. Try sketching what you are seeing and then go to a photo of that view. The times and dates for when different areas are pointed at earth are published, so you can compare. There are even Mars globes available if you really get into Mars.
Jupiter: This is my favorite planet. Jupiter has it all. It is big, it is bright, it is beautiful, it has moons, and it is constantly changing. Even a newbie observer will be able to see this huge gas giant has large cloud bands and four brilliantly lit moons moving around it. It is by far the largest planet in the solar system and presents the largest face to observers, and has a day of 10 hours so you can see all of it in about 5 hours.
The planet has a huge variety of colors from white to tan to blue to red. The largest bands on it constantly change, with its overall appeearance having practically reversed since Pioneer 10 photographed it in the mid 1970s. Month to month huge storms form and new features appear and vanish. For example, last year, the northern band started forming deep red spots along one edge. The southern band disappears and re-forms periodically, while the great red spot changes color (it has been a sort of beige the last 25 years) and size over time. The stripes are full of swirls and other cloud formations in various colors.
The moons are constantly in motion, and their colors are visible. Io, the closest to the planet, is sulfur yellow from its volcanoes. The moons also pass in front of the planet and produce easily visible shadows on the surface. You can make 3D pictures of Jupiter by snapping one frame, waiting ten minutes, and snapping another. The rotation of the planet is fast enough to get a stereoscopic effect between the two images. This can give very strong depth effects when one of the moons is in front of the planet since the moons move in the direction the planet is rotating so you get a very real perception of the moon above the surfaces with the shadow on the planet below. Although the planet has a host of tiny moons in addition to the big four, I don't know of anyone who has positively found the smaller ones with a small telescope. It is far more likely you will have found a background star the planet is lined up with by accident. Jupiter is a good place to gain experience finding details. The fact you won't have an up-to date photograph to look at makes it much more challenging and interesting.
Saturn: This is easily the most photogenic planet in the solar system. Saturn is substantively smaller than Jupiter and is smaller away, so the entire width of the planet and its rings is approximately equal to Jupiter. The main draw for this planet is, of course, its beautiful and magnificent rings, which even small telescopes will show. The real treat starts at 80mm and larger diameter scopes where it becomes possible to see the Cassini division in the rings and pick up on the the gradient detail in the rings themselves. However, unlike Jupiter, Saturn doesn't to have the trick of always changing. This world is a gas giant in shades of tan with a white cummerbund. When the seeing is incredibly clear, the planet does have texture to ids cloud bands, and the rings show up as having some color and texture as well. Over an 8 year period, Saturn wobbles up and down from our point of view as it moves in its orbit. The rings will appear to be edge on every 4 years and are at their maximum tilt to us this year.
Unlike Jupiter, Saturn has a selection of moons in different sizes different telescopes can see. A 80 mm scope will show the largest moon, Titan. The moons are in the same plane as the rings, so they appear to move around the planet in an oval when seen from earth. Several smaller moons are visible when the seeing is good, and they are never in the same spot night to night. Saturn, like Jupiter, is a perfect training ground for observing, and like Jupiter, has great stuff to see even when you are starting out.
Uranus: Uranus has that dopey joke, and it's really not fair since it is a neat object to look at. This is a gas giant planet smaller than Jupiter and Saturn. It is unusual since its axis is on its side, possibly indicating the planet was hit by something enormous early on. The planet slowly moves in the sky and is currently in the general neighborhood of Neptune in the sky, so I suggest looking for them on the same night.
This planet is very far from the sun, so there is much less light. There is also a big difference in distance between how far Saturn is from earth and how far Uranus is. As a result, even though it is a huge planet, all you will see in the telescope is a little green ball. Two nice things about this planet are how obviously spherical it looks and how green it is. There are very few objects in the sky with actual green in their color, so this pistachio ice-cream colored world is a nice change. There isn't any surface detail to see, but it is obviously a planet.
Neptune: This is the farthest out of the gas giants, and has the distinction of being found entirely by its influence on another planet's orbit- Uranus. This world is a little smaller than Uranus and is again further out, so there is little light, and it is really far away. It alternates with Pluto for being the most distant object in the solar system. This planet looked to me sort of like the period on a sentence. You can tell it is round and not a star, and it is obviously a turquois blue color. I didn't feel complete as an observer until I had found it, but I have to admit it is a little like "Once you've been there, you may or may not care about going back." I think I need to see it in a really big scope since I found it in a 5" scope, so I will take a crack at that and update this later.
Pluto: I don't have a very good story for this one. I've looked for Pluto, and I'm pretty sure I've looked at the right spot in the sky, but going from the map to the view, I can't decide if I have found dim stars not plotted on that particular map or if I have seen Pluto. All I can say is Clyde Tombaugh (the discoverer) must have been one bad man to find it back when he did.
Stars
Stars other than the sun are all at extreme range. As a result, they are so small seen from earth that they appear to be perfect point sources of light. Only extremely large telescopes such as Hubble and Keck have succeeded in resolving other stars as disks. When viewing a star, you will get an image based on the minimum resolving capability of the telescope you are using. At high magnification, the star will turn into a tiny disk with some dim diffraction rings around it (it will look a little like a Target store logo). What you are seeing is an image of the telescope's optics. The disk is what is called the Airy disk, after Charles Airy who first recognized its significance. If you are using a telescope with a central obstruction (a secondary mirror, such as a Newtonian, Schmidt Cassegrain, or a Maksutov), the first diffraction ring around the Airy disk will be brighter than the others. The larger the diameter of the central obstruction compared to the diameter of the telescope, the brighter this first ring will be. This image is sensitive enough to be able to collimate the telescope using it, and some manufacturers, such as Celestron, actually instruct people to do just that so the telescope is in perfect alignment.
Now, there is a temptation to expect stars to be boring because of this. However, the stars have some tricks up their sleeves.
First, stars come in colors. Most people who have never become familiar with the night sky think of the stars as being white points of light in the sky. However, they actually are all colored, and once you have learned to see this, you can recognize them immediately. For example, Betelgeuse in Orion is a deep orange color. Rigel, at the other end, is bluish white. Sirius, following Orion across the sky is pure white and bright. North of Orion, Capella is yellow like the Sun.
When seen through a telescope, the colors are much more evident. There are even some dim red dwarf stars which are as pure a red as an LED when you happen across them. New stars are brilliant blue-white, like the brand new stars making up the Plieades. After a little practice, you will be able to pick up on star color with and without a telescope and the night sky will never look the same again.
The second phenomenon with stars is double, triple, and quadruple stars populate the sky. Practically every constellation has several interesting double stars. Most of these really are in orbit around each other, so they are exactly what they sound like, rather than being an optical illusion caused by a star near to us accidently being lined up with something further away. Current estimates are about half of all stars are doubles. Polaris, the north star, is a double with a dim companion nearby. In the Big Dipper, there is an intersting double in the middle of the handle called Alcor and Mizar. These stars are an obvious double in low power binoculars. However, zooming in with a telescope will show there are, in fact, three stars as one the stars visible at low power is actually two stars close to each other. There are also doubles with radical color differences between the stars. For example, Albiero is just dimly visible in most suburban skies, but in a telescope it turns out to be a bright yellow star with a dimmer blue companion.
Double stars also change with time. Periodically magazines such as Sky and Telescope and Astronomy will put in articles with star movements shown in them, and there are some web sites which show this. If you wanted, you could look through these lists for a pair which orbit each other in a reasonable period of time, and take a few photos of them each year. You would have a movie of the star's movement a while later (as far as I know, no one has done this yet- it may take many years to complete one depending on how long the orbit takes). However, no one had photographed the sun's periodic movement in earth's sky until the 1970s (the sun tracks a figure 8 in the sky if you photograph it at the same time of day every couple days for a year).
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Member: Rich W.
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