How to Safely See a Partial Solar Eclipse

Partial solar eclipse
This view of the partially eclipsed Sun was made through a metal-coated glass filter, which produces a yellow or orange image of the Sun; most aluminized Mylar filters give a blue image.
S&T: Edwin Aguirre

Looking at the Sun is harmful to your eyes at any time, partial eclipse or no. The danger that a partial solar eclipse poses is simply that it may prompt people to gaze at the Sun, something they wouldn't normally do. The result can be "eclipse blindness," a serious eye injury that can leave temporary or permanent blurred vision or blind spots at the center of your view. Fortunately, there are many easy ways to watch the show safely.

Pinhole Projection

The simplest safe way to view a partial solar eclipse is to watch the Sun's image projected onto a piece of paper. Poke a small hole in an index card with a pencil point, face it toward the Sun, and hold a second card three or four feet behind it in its shadow. The hole will project a small image of the Sun's disk onto the lower card. This image will go through all the phases of the eclipse, just as the real Sun does. Experiment with different size holes. A large hole makes the image bright but fuzzy; a small hole makes it dim but sharp.

Pinhole projection
Sky & Telescope illustration
For a better view, you can reduce the amount of daylight shining on the viewing card by enclosing it in a long box (left). This lets you use a small pinhole giving a sharp image.

A much better way to do pinhole projection can be arranged at a window indoors. Find a room with a Sun-facing window, turn out any lights, and pull the shades. Arrange for sunlight to enter through a small hole punched in a card near the top of the window. Set up a white piece of paper across the room to catch the Sun's image. Again, experiment with different size holes to get the best, sharpest view. (Of course, don't look through the hole directly at the Sun! Look only at the spot of light that falls on the paper.)

If the Sun is too high in the sky for this, you can direct its image horizontally into the room by setting up a small, high-quality mirror on the sill of an open window. Hold the mirror in place with modeling clay. Tape your card with the hole right onto the mirror.

Even at its best, pinhole projection gives only a small image. The throw distance in feet, divided by 9, gives the image diameter in inches. Pretty small!

Project a Partial Solar Eclipse with Binoculars or a Telescope

Solar projection
Sky & Telescope illustration

You can form a much sharper and bigger Sun image by projection through a small telescope or binoculars (right). This is best done outdoors to avoid the distorting effect of a windowpane. To aim the instrument safely, look at its shadow on a white card as you swing the tube around. (Don't use your finderscope — make sure it's capped at the front end or removed completely.) When the scope's shadow nears its minimum size, a brilliant beam of sunlight will burst out of the eyepiece and fall onto the card. Turn the focus knob and experiment with the card's distance behind the eyepiece until the Sun's disk is sharp and as big as you want. Look for sunspots!

How to Directly View a Partial Solar Eclipse

Viewing the Sun with special eclipse glasses
Johnny Horne

If you prefer to look directly at the Sun, you can use a square or rectangular arc-welder's glass of shade #13 or #14, available for a few dollars from local welding-supply stores. (Don't get a lower-numbered shade; the Sun will be too bright to look at safely.) Alternatively, special, cheap "eclipse glasses" (left) are widely made from safe solar filter materials.

A solar filter that's designed to be used with a telescope is also safe for viewing with the otherwise unaided eye.

Filters that are not necessarily safe, though sometimes recommended in old books, include smoked glass, stacked sunglasses, crossed polarizing shades, photographic neutral-density filters, or a filter intended to block visible light for infrared photography. While these may greatly dim the Sun's glare, thus appearing to do the job, invisible ultraviolet or infrared radiation may be getting through to damage your eyes. (See "Solar Filter Safety" for more details.)

Solar filter on a telescope
Richard Tresch Fienberg

Telescopic viewing. The clearest and best views of the Sun are had through a properly filtered telescope. Sky & Telescope reviewed commercial solar filters designed for telescopes in the July 1999 issue ("Solar Filters: Which is Best?") and September 2000 ("Baader AstroSolar Safety Film: A New Standard in Solar Filters").

The filter must be secured over the telescope's front to keep most of the Sun's light and heat out of the instrument. Never use a Sun filter at the eye end, where it could crack or melt in the concentrated heat.

Direct viewing with a telescope and proper solar filter gives the best views of sunspots and the complex details within them, as well as the progress of the Moon's jagged, mountainous edge making its way across the solar disk.

Remember, safety is paramount. Never look directly at the Sun without using a safe solar filter. If you don't have one, see our list of suppliers.

3 thoughts on “How to Safely See a Partial Solar Eclipse

  1. GaryWall

    One meter image of eclipse: Use a Newtonian or Dobsonian telescope to project suns image: Refractor scope needs a mirror.
    1. Make a mask for the front of your scope. Otherwise 100 power sun image will melt inside of scope.
    I melted the edge of the eyepiece holder first lens on my scope. Also the eyepiece lens is cracked.
    I found a black plastic bowl from a restaurant that fits scope. I cut out the bottom so if fits snug over the barrel and taped it on. The bowl lid snaps over the bottom to make an easily removable sun mask.
    The fast food bowl lid is typically clear. It must be blacked out some way Cut a hole in the SIDE of the lid. [ the center of scope has a mirror] Actually any cardboard etc cover will work.

    WEAR GOOD SUNGLASSES always. Being around any concentrated sun image will dazzle your eyes
    Wear a long sleeved shirt. Then you will smell the burning fabric if you get in the way of a sunbeam.

    2. make a “rifle sight” scope aimer. Use wire coat hanger etc to wrap around front of scope. Twist the wire so it sticks up a couple inches. At back of scope attach a large card. The shadow of the wire is where scope is aimed. You can adjust this and mark center point of shadow. Look at the eyepiece from the side to see the sun image. NEVER LOOK IN THE EYEPIECE!! When the “hot spot’ is centered scope is aimed right.

    3. Hold a card near the eyepiece to focus small sun image.

    4. Projection “room” In the morning or afternoon you can aim scope out an open window to East or West. Project sun image on a white wall. This won’t work with this eclipse as it is near noon. the telescope must be outside then shoot the image into a darkened area.
    I set scope up behind my SUV Tahoe open back doors. Set up movie projector screen or white cardboard or foam board. I got a nice one meter image. Could see sun spots in an eclipse 10 years ago. Any darkened space works well. You can use a tent or a trailer or an appliance cardboard box. Cover the tent or SUV side and front windows with tarp to make it darker.
    BE VERY CAREFUL! You will be blinded just looking at an eclipse. A telescope magnified image will “burn a hole thru your head” I will send photos [not of hole in my head !! ]

  2. GaryWall

    { Alan: I Sent photos of telescope projector emailed to Editors at S&T ] If you want to do a better set up and take photos, you could get national publicity and increase magazine subscriptions. A million people have telescopes in their basement. This may get them in use. Try a local TV station with a live Sun projection. demo. Weather segment on news would work. Work out the bugs, then go National and International coverage. I looked all over the Internet and nobody is doing this “Giant Eclipse image” Even NASA! Works great
    I will contact KSL TV in Salt Lake. Been on there 5 times on earthquakes . Last time, we had a quake they felt the next morning!! ] Post follows:
    About photos.
    EYE SAFETY: PAINLESS PERMANANT EYE DAMAGE. FROM JUST LOOKING AT ECLIPSE 100X SUNBEAM FROM TELESCOPE WILL BURN A HOLE IN YOUR BRAIN ! !
    1. Don’t use a really good telescope for Eclipse projector. You are “playing with fire” 2″ scope is plenty big. Scope in photos is a old Celestron 4.5 inch Newtonian with a wide angle eyepiece.
    2. Note twisted copper wire at front of scope. Note “card” 8 inch approx square at back of scope. The shadow of wire aims scope. Note eyepiece with bright sun image in center when zeroed in. Sun mask at front of scope is not installed.
    My trailer door swung open and knocked over telescope. Landed on eyepiece, bent the heck out of sheet metal 4 1/2 main tube. I pounded out worst of dents over a log. {we are really high tech] Now will drill new eyepiece hole with 1 3/4 inch hole saw in an undamaged area. Good news is at the inside of the eyepiece, i found the concentrated Sun beam slightlty melted the inner lens ring. So now will only use wtih 80% mask on front of scope. I might remove mask for a few seconds during eclipse totality.
    There are currently no sunspots. Check SpaceWeather sites for daily Sun image reports. When I set this up some years ago Sunspots were really cool. . . or Hot!
    BE CAREFUL and enjoy !

    1. GaryWall

      Telescope used is old Celestron 4.5 inch Newtonian reflector. Eyepiece is 25 mm Wide Angle, 8 foot distance from eyepiece to wall in photos. Sun image is maybe 38 inches. Photo at 9 AM. but Eclipse at 11AM. So this “out the East window” set up shown won’t work. Use a North facing windo or door, or porch. Put scope outside.
      There are web sites with tables and calculations for Sun image size calculations with dirrerent lens and scopes.
      For really simple Sun Eclipse projector I will try a ladies magnifying make up mirror. Make that into a reflector telescope. Focus to a mirror then lens. The $10 mirror will give a decent eclipse image, but not as good as a real accurate telescope mirror. BE CAREFUL. Burned holes in my shirt with said mirror in Morse Code Heliograph tests!!

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