So we are either a) setting up and cursing our solar projection system, b) cursing at the clouds, c) wondering how we can live to the year 2117, d) wondering why we didn’t make such a fuss for the 2004 Venus transit.
With the just passed annular eclipse out in the Western part of the USA a couple of weekends ago and the upcoming transition of Venus you might be inclined to buy a fancy solar filter for that telescope.
Well there might be a problem with that. See everyone else had the same idea as you, and that means the manufacturers of such filters are pretty much out of stock! It can even be hard to find just the filter material! What to do?
Well, there is another way of viewing the sun without the use of a filter. It can be tricky and it can be dangerous if proper care is not taken. That method is called projection astronomy. This is where you use the telescope & eyepiece to actually project the image you would normally see with your eye onto a board or other bright surface.
What do you need? You need a telescope with an eyepiece (preferably lower-medium powered), a sunny day, and something to project the image onto.
We came up with this kind of last minute, so we just used a flat box on a clipboard. It had problems with the box seams, but the surface was very bright (brighter than the average piece of printer paper) and so would give a decent image.
Next up, we need a telescope. We used an Orion StarBlast 6 , mostly because that is what we had around the store.
Note that the picture above shows the telescope in action. When setting it up and aiming it you should LEAVE THE DUST COVER ON. This is the best thing for your safety.
Aiming your telescope at the sun is pretty easy, just try to get your tube to make the smallest shadow possible. When you think you are on target, remove the dust cover and see if there is any light coming through the eyepiece. DO NOT look into the eyepiece, ALSO DO NOT LOOK DOWN THE AT THE EYEPIECE. View it from the side. We are not responsible for your losing your eyesight!!!
Now a further safety warning: Try to avoid getting any body parts in the path of the light coming out of the eyepiece. Hold the board on the edge, work around the telescope, not over it, etc.
So now that you are lined up with the sun, you can see what kind of image you have. Place the projection board about a foot or so away from the eyepiece. Move it closer or further away to try and get it into focus. DO NOT bring it closer than 6 inches from the eyepiece, the light is a little too concentrated there and some types of paper might burn.
Some adjusting will be needed. It is best to move the screen rather than the telescope. If you must adjust the focuser, put the dust cover over the front of the telescope.
So what kind of view so you get? Well, here is a shot of the screen that is a little closer than the last photo:
This didn’t show up too well in the photo, but if you look closely, you can see some sunspots projected on to the board to the right and right/down of the center.
How well will projection astronomy work on the transit of Venus? We don’t know for certain. The sun will be very low in the sky and there may be more distortion or discoloration as a result. But if you have the time and the telescope, this isn’t exactly an expensive experiment! Just remember to be careful! Pointing a telescope at the sun always has risks – just use common sense and keep out of the path of the projected sunlight and you should be fine!
So, yesterday the Western part of the USA got to enjoy an annular eclipse…NO WE ARE NOT BITTER!
In any case, this is not the only solar event for us this year, because on June 5-6th there is the Transit of Venus!.
A transit is when one of the inner planets (which is pretty much just Mercury and Venus) moves between the Earth and the Sun. A small shadow of that planet can then be seen through a filtered telescope. The last transit of Venus was only just in 2004, but the next will be in 2117! So don’t miss it.
Remember that looking at the unfiltered sun is very dangerous. Always use a filtered telescope or a projection system to view the sun!
The transit will be visible through the entire United States (and Canada & much of Central America) during the evening/sunset on June 5th. The transit will be in progress when the sun sets. Most of Europe will be able to see the transit on the morning of June 6th. Parts of Asia, Australia and Alaska will be able to see the whole transit.
Don’t miss it!
Its a bit hard to write about a solar eclipse when the rain is falling, and doubly so when the viewing area is not where you live. But this is a rather important astronomical event and many readers might be in a position to actually see it. We are talking about the Sunday, May 20th annular solar eclipse.
Annular eclipses are when the Moon is positioned in front of the sun, but unlike total eclipses the sun is not completely blocked due to the Moon being further away than in a total eclipse. This means a reduced apparent diameter and results in the “ring of fire’ appearance.
The majority of this eclipse will take place over the Pacific Ocean, and only portions of the Western part of the USA will be able to see it take place close to sundown. Here is a rough map of the areas that can view a portion of this eclipse:
Folks in Alberquerque have all the luck!
Remember that special care should be taken to view an eclipse – view either via a projection method or with a properly made solar filter or eclipse glasses. Do NOT try to view using sunglasses. Even at sundown the sun can be excessively bright and harmful to your eyes.
Enjoy the eclipse if you can!
One of the more wide-range things to use in astronomy are filters. There are a large number of them and their purpose varies greatly. They can reduce light, help with light pollution, bing out details, or help with astrophotography. Most filters thread on easily to telescope’s eyepieces and can change your viewing experience.
But when choosing filters one must remember this: They are filters, they are designed to remove something, even if it is unwanted. Some folks get the idea, especially with light-pollution filters, that filters make objects being viewed much brighter. But that is not the case. Think of it this way: if you have a kitchen odds are ou might have a water filter in your faucet or some kind of pitcher. When you use this filter you do not make more water by using it, you are merely removing the stuff in the water you do not want. Water filters are actually pretty good because if you put 1 liter of water over a water filter odds are you will end up with very close to 1 liter of clean water. But you won’t end up with 1.1 liters. Sounds obvious, but some folks get the idea that that is what astronomy filters can do. But it is not so. In fact using an astronomy filter on the light from the stars means you are going to lose some of the good light along with the stuff you do not want. If we go back to out water filter you can think of our 1 liter of unfiltered water becoming .9 or even .8 of a liter.
But let us discuss the various types of filters:
Moon filters are simple neutral density filters (which means they evenly cut down on light across the visible spectrum) that thread onto your eyepiece. They are used because the Moon is actually very, very bright and viewing it in even small telescopes at it can hurt your eyes after a short time (not permanently, mind you). A Moon Filter can make viewing more comfortable. Typically filters allow in 25% of the light, or 12% (for larger telescopes) or in a variable model you adjust yourself .
Solar filters are the only filters that do not thread onto the eyepiece. The go over front of the telescope. If you find a ‘solar filter’ that is meant to thread onto an eyepiece, destroy it immediately. Those are very dangerous as they can crack letting through sunlight that can damage your eyes. Don’t use them, Don’t keep them – someone else might be tempted. Destroy them.
Most solar filters are simple screens of Mylar that cuts down on 99.999% of the light so that you can safely view the sun. Mostly what you will see is a white disc with some sunspots. It makes for some nice viewing during the high points of the sunspot cycles, during the lows the sun can seem a bit featureless, however.
Another type of Solar Filter is the Hydrogen-Alpha Filter. These allow you to view reddish colored prominences and solar flares. They are very expensive, however (in the thousands of dollars) and they need a certain amount of ‘tweaking’. But they can give very impressive views of solar activity.
Color Filters are used on the planets or the Moon – they cut off too much light to use on deep sky objects. Color filters are used to try and bring out more details on the planets that might get washed out in regular filtering. Details brought out might include the bands on Jupiter, polar caps on Mars, more lunar crater detail, and so on. Color filters can be hit-or-miss among astronomers. Some think they are great, others find them less useful. The field seems rather subjective but if you plan on viewing the Moon & Planets more than anything else you might wish to invest in a set.
Light Pollution Filters
Light Pollution Filters are designed to help astronomers who live in light-polluted suburbs or cities. They are not a substitute for dark skies, but they can certainly help out when options are limited. Light pollution filters help by cutting down on frequencies of light that streetlights, parking lot lights, and other human-made light sources produce, while letting through most of the light that stars, nebulea, and other deep sky objects emit.
This set of quickie photos can give you and idea of the effect of the filters. Here is a shot of a city streetlamp that is on during the daytime:
And then with an Orion Ultrablock Filer held over the lens:
You will notice that the filter helps, but does not completely eliminate the streetlight light, and it does have some effect on the natural background light as well. This is why they are helpful but not a complete solution to dark skies.
Light Pollution filters also are of little use on the Moon (which is bright enough to not be bothered by light pollution) or the major planets (which are similarly unaffected by light pollution). They are of limited effect on the outer planets as those planets emit light over much of the spectrum and get filtered as much as the background light.Some light pollution filters may be referred to as Nebula filters, which are very focused and are even designed to cut down on some of the light from nearby stars.
There are a huge number of these and their uses could fill a book – a book about astrophotography that is. These filters do things like cut off the IR portion of the spectrum (which messes up CCD chips in digital cameras) or filters out only the all but the Red or Green or Blue part of the spectrum for monochromatic cameras. The number of these filters has expanded vastly in the past few years. Covering these would take a very large entry so we will leave them for now as it is beyond the scope of Astronomy Hints.
Refractor Violet Filters
These filters are for one type of telescope – refractors. The large lenses in these telescope sometimes act as prisms and break up the light into component colors. This is especially noticeable on bright objects like Jupiter or the star Sirius. The effect is that the object being viewed will have a violet colored halo that is affectionately known as ‘purple haze’. Violet-Minus filters cut out this portion of the spectrum without affecting overall viewing much. If you have a larger refractor that sometimes shows the ourple haze you might consider getting one of these filters.
…oh right! We were telling folks how to get a paper sundial printed out. Well we got ours all printed out and happy. We cut it out and folded it up.
…and realized it would not last through the first drizzle. This would be a problem as summer rains happen almost daily at this point. So what to do?
Well, in our case we printed out another sundial and put it through the lamination machine! Now it was covered in plastic and protect from the elements, at least for a while. If you don’t have a lamination machine (most people don’t) then clear packing tape can help protect your sundial. Its up to you if it is easier to apply the tape before or after you cut it out. We certainly had to put the paper through the laminator before cutting it out (jammed lamination machines tend to burn).
Once we cut out the laminated sundial and taped it together we put it on the wall. Then we discovered there was a problem. Our store’s outdoor walls don’t have a lot of places where there are not other objects that case shadows on the sundial’s space. Take a look:
OK. so the big shadow you see is from the canopy of the store next to ours. During much of the day it completely covers the sundial’s shadow. But for a few hours the thing does a nice job of giving you the time. Take note that it does show time in a 24 hour clock pattern.
Hopefully you will have better luck than we did and have a non-shadowed space.