Find Objects by Star Hopping

It's not hard to find the Orion Nebula or the Pleiades with your binoculars because they are bright enough to see without magnification.  Look straight at them without help, then put your binoculars in front of your eyes.  With just a little practice, the object will appear in the binocular view the same as naked-eye, only bigger.

On the other hand, finding objects too dim to see naked-eye is challenging to most new observers.  How do you find something that is too dim to see without magnification?  The easy answer is to point at the bright star right next to it and hope you can see the dim object too.  But what if it is not right next to a bright star?

The trick is "Star Hopping".  This article will teach you how to hop from bright naked-eye objects right to the dim objects you're wanting to find.  We'll use a technique practiced by experienced amateur astronomers for generations.

Star hopping is a technique to find objects too dim to see naked eye by "hopping" from objects that you can see without optical aids.  Most objects can be found with 2-3 "hops".  The trick is to know how far to hop and in which direction.  As my high school math teacher told me, once you know the "trick", it becomes a technique you can use over and over again.  I'm going to teach you the technique of star hopping so you can add it to your bag of tricks and become a better amateur astronomer.

In this lesson, I'm going to describe how to star hop using binoculars to find M14, a globular cluster in the constellation Ophiuchus. It is one of the "Tougher" Messier objects in the Binocular Messier Club list and a great target for this trick.  The technique applies when using a telescope finder scope too.  Learn to star hop with your binos and it will be much easier with your telescope.

What You Need

• Star Atlas
• Binoculars
• Field of View Template

Get yourself a star atlas that will show more stars than you can see naked-eye.  Most of us observe where we can see somewhere between magnitude 3 or 4.  Travel to a dark sky location and you might be able to see magnitude 6.  I suggest picking a star chart that shows stars to magnitude 7 or 8.  My favorite is the Pocket Sky Atlas or PSA.  I bring this with me every time I go out observing.  It shows stars to magnitude 7.6.  In my binoculars, I can see slightly more dim stars so the PSA works well for star hopping.

The next thing you need to understand is the field of view using your binoculars.  The field of view, or FOV, tells you how much of the sky you can see when looking through the device.  A simple way to think of this is to hold your arms straight out, pointing your fingers toward the sky.  Put your hands close together and the angle of your arms is small.  The view of the sky between your hands is also small.  Separate your hands to make the angle of your arms bigger and your view of the sky is proportionally bigger as well.  Your binoculars show you a view of the sky that's just a little bigger than the width of your fist held up to the sky at arms length.  That's about 5º or so.

Have a look at the markings on your binoculars to know the exact field of view.  The spec for the FOV is probably printed on the outside.  For instance, my Nikon 10x50 binoculars have a field of view of 6.5º.  If I put a star on the edge of my view when looking through my binoculars, I can see other stars that are 6.5º away or closer.  

Now go back to your star chart.  How big is 6.5º on the chart?  The PSA has a a scale on the inside front cover from which you can estimate with your thumb and index finger.  That might work but it's difficult to hold your fingers still as you turn pages in the atlas.  Here's a better idea: Make a FOV Template.  It's pretty easy.  I recycled a tan manila folder by drawing circles that matched the FOV of my binoculars and telescope finder scope.  I cut out the circles with an X-acto knife.  Now I can hold my FOV Template over the chart to know with good precision what I should see when I look though my binoculars.  Click these images to get a better view.

I'm going to continue this tutorial using my binoculars and the Pocket Sky Atlas.  You need to make a FOV template that matches your atlas and binoculars.  Do it now as it will continue to be useful after you've become skilled at star hopping.

Star Hop in Pocket Sky Atlas

Let's try our first star hop using the Pocket Sky Atlas to find M14, a globular cluster in the constellation Ophiuchus.  When planning a star hop, the magic of this technique is to plan your hop in the atlas.  In the atlas, we chart the hops by working backwards from your target to a bright star that you can find without aid.  In the case of M14, the nearest bright star is Cebalrai.  It's about 8º north of M14.  When we look at the bright star, our target is just out of sight.  This makes M14 a perfect target for learning to star hop.

Working backwards: Find M14 on page 54 of the PSA. Using your FOV Template, find a route from the target using distinct star patterns or asterisms to the bright star Cebalrai.  The distance to each asterism has to be less than the FOV of the binoculars, preferably just a little less. Click the image to see the route I have chosen.

Notice the pair of mag-5 stars to the North-east of M14. The movement between this pair and M14 is the first hop of our route back towards the starting point therefore it will be the last hop when we move the binoculars under the stars.

Now move the FOV Template north, towards Cebalrai. Move slowly to keep the star pair in the FOV. When the southern most of the two are at about 4 o'clock position on a clock see the mag-4 star opposite the star pair at about 10 o'clock.  It is labeled with a stylized 'y'.  This is the Greek letter Gamma, described on page xii in the PSA.  This star is called gamma-Ophiuchi. This will be the next hop.

Continue moving the FOV Template north and see the bright mag-3 star Cebalrai come into view. Center it and remember this view. It is starting point for the star hop using binoculars.

Now let's do it again.   This time in the order that it will be done when we move outside under the sky. Unless you have moved it, your FOV Template will have the mag-3 star Cebalrai centered the circle cutout of your FOV Template for your binoculars. It should match the image immediately above.  Notice the gamma-Ophiuchi nearby.

Now slowly move your FOV Template down and a little right until gamma-Ophiuchi is on the edge but still visible at about 11 o'clock.  You should see the two mag-5 stars on the opposite edge at about 3 and 4 o'clock.  This is your first star hop.

Now make your second star hop by slowly moving the FOV Template down until the star that was previously at 3 o'clock is at 2 o'clock, still very much in view.  M14 should just about be center in your Field of View.  You found it!

This is a how to hop in the star atlas.  Next try it with your binoculars.

Star Hop with Binoculars

It's almost the same but with a couple of minor differences.  First start by finding the mag-3 star Cebalrai in the Ophiuchus.  Notice the gamma-Ophiuchi just south and a little east.  That's the first difference from hopping with binoculars versus using the chart.  You will have to do a translation when moving from the atlas to the sky.  Left-right, up-down will mean different things depending on the time of night and even during changing  seasons because the constellations are in different places in the sky as time passes.  Here's what it looks like using the computer star charting program Stellarium.  This image is configured for a FOV of 6.5º and magnification of 10x, matching the binoculars used in this tutorial.

Make the first hop by slowly moving your binoculars south and a little west until gamma-Ophiuchi is on the edge of your view but still visible.  Call this 11 o'clock. However, it may actually not appear at the 11 o'clock location of a clock depending on when and where you are observing.  Let's just call it's position 11 o'clock to be consistent with our atlas star hopping.  Stay steady and notice the two mag-5 stars on the opposite edge that we will call 3 and 4 o'clock.

Now make your second hop by slowly moving your binoculars south until the star that was previously at 4 o'clock is at 2 o'clock, keeping both in view.  M14 should be about center in your binocular field of view.  Messier 14 is magnitude 7.6.  That's dim, so it won't be obvious to spot it with binoculars, but it will be visible except in locations with lots of light pollution.  I've included two images below that show M14 center of the binocular view.  The second is clearly marked, the first is not.

You've just learned a two-jump star hop with binoculars.  Try to repeat it several times until you can move each hop with confidence.

Experiment by Finding Others

Try another object in the Binocular Messier club list. First with your FOV Template and star atlas.  Then repeat with your binos.  Here's a couple of suggestions from the Binocular Messier list:

• M10
• M33
• M75

These are in the "Easier", "Tougher" and "Challenge" Messier lists respectively.  Keep practicing and you'll find this trick has become a natural technique that helps you find many objects that would previously have been pretty difficult because of their location far from bright stars.

Tell me what you've found using star hops by leaving a message in the comments below.  Brag a little.  Tell me what was a challenge.

Remember to record what you've found at AstronomyLog.com.

Wishing you clear skies and warm toes,

-Bob

bob@astronomylog.com

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How to star hop to find stars and other astronomy objects.

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