# Solar eclipses: partial vs totality **URL:** \ **Category:** Factual Questions\ **Created:** [March 20, 2017, 5:55am UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593 "2017-03-20T05:55:32Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 23, 2017, 10:27am UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/61 "2017-03-23T10:27:12Z")
> [@Francis\_Vaughan](#): > > Easy answer. Go for the best chance of seeing it. Exactly this. Don’t worry about the longest duration, worry about the best chance of clear skies. Even places only just inside the path will still see a decent duration (and in fact you can get cooler effects when you are close to the edge of the path of totality, as you tend to get a longer “diamond ring” phase). ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 23, 2017, 10:32am UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/62 "2017-03-23T10:32:21Z")
> [@Flyer](#): > > It’s pretty thoughtless and rude to bark at somebody “Just go no matter what!” without considering that many millions of people simply **are not able** to do something like that. > > It’s not “worth it” if you lose your job for an unexcused absence from work. It’s not “worth it” if you don’t have the money to make the trip. > > Sure, I’m confident that it’s an awe-inspiring sight, and I would like to see it. But you know what? I can live just fine without it. There are a great many things in life that are vastly more important. If I never get to see a total eclipse, that probably isn’t going to even crack the top 20 regrets that I’ll have when I’m on my deathbed. > > Judging by the responses in this thread, most Dopers have absolutely no clue how most people in this country live. And many of you also have a really messed-up sense of priorities. Considering you asked the question, you clearly have at least thought about driving far enough to see totality, so I don’t see why you are offended by the enthusiasm of people saying you should go. Don’t take it personally. If you don’t want to or can’t justify it, then don’t. And I agree with the others. Either drive all the way into the zone of totality (if you can afford the time and money, of course), or stay put. Driving from 89% to 95%, say, is about as pointless as driving halfway to the Grand Canyon. 🙂 ---
**Author:** ![Bumbershoot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bumbershoot/32/3428_2.png) [@Bumbershoot](https://boards.straightdope.com/u/Bumbershoot)\ **Post date:** [March 23, 2017, 2:04pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/63 "2017-03-23T14:04:04Z")
I’m going to be in eastern Idaho for the eclipse- some friends live very close to the line of totality, according to Jubier’s map (linked in post #35 by Bullitt). In fact, they’re just 750 feet north of the line. The guy who lives there (let’s call him Dave since that’s his name) is really into photography. Dave is reading everything he can find on eclipse photography. Another friend (Paul) is flying to Albuquerque and we are going to take a nice road trip through Utah, ending up in Idaho a couple of days before the eclipse. Paul is also really into photography. Dave’s wife Terri and I will be simply observing. Would it be worth it for us to move 750 feet down the road and set up the cameras or can we get the same results from Dave’s backyard? Jubier’s map lists an Umbral depth of 99.6% for Dave’s backyard. Does that mean just 750 feet north of the line is 99.6% of totality? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 23, 2017, 2:18pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/64 "2017-03-23T14:18:14Z")
I don’t know the exact width of the path of totality of this eclipse, but think in the range of tens of miles (but less than hundreds.) So 750 feet will make essentially jack squat difference. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [March 23, 2017, 2:58pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/65 "2017-03-23T14:58:07Z")
No, 750 feet away will be driving half way to the Grand Canyon\*. The edge of totality gets totality for an instant. Anything outside of that gets exactly nothing\*\*. You need to be inside the path of totality with some margin in order to get the totality to last longer than zero seconds. The increase in totality time increases pretty steeply on the edge of the path, but as you get closer to the middle the gains slow down enough that getting to the exact middle isn’t a big deal. But plan on wanting to get maybe 5 miles in. - Brilliant phrase. 😃 \*\* Don’t underestimate the power of the sunlight coming through even the most tiny of cracks. 99.6% totality means 0.4% of full intensity sunlight. That is still a huge amount of light. The sun is roughly a million times as intense as moonlight. 0.4% sunlight is 4000 times as bright as the full moon. That is still way too bright to see much of anything in the corona, or really experience the darkness. ---
**Author:** ![Bumbershoot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bumbershoot/32/3428_2.png) [@Bumbershoot](https://boards.straightdope.com/u/Bumbershoot)\ **Post date:** [March 23, 2017, 2:58pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/66 "2017-03-23T14:58:12Z")
I was playing around with Jubier’s map and just 95 feet north or south of the blue line gives an umbral depth of 99.95%. Does that mean that three people, one standing directly on the blue line and the other two 95 feet north and south of person #1 will have different experiences? The blue line is that precise? ---
**Author:** ![Bumbershoot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bumbershoot/32/3428_2.png) [@Bumbershoot](https://boards.straightdope.com/u/Bumbershoot)\ **Post date:** [March 23, 2017, 3:09pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/67 "2017-03-23T15:09:02Z")
Here’s another link to Jubier’s map in case anyone else wants to play around with it: [Xavier Jubier’s Eclipse Map](http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2017_GoogleMapFull.html) ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [March 23, 2017, 3:20pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/68 "2017-03-23T15:20:42Z")
Given the Sun’s photosphere is a trifle indistinct, the moon isn’t a perfect sphere and the Earth has an atmosphere, the line of totality isn’t absolutely black and white. However, you can see the shadow on the land approaching if you have a good vantage point. The edge might be a bit indistinct, but there really is an edge. You are either in the shadow or not with not a great deal of wiggle room. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [March 23, 2017, 3:21pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/69 "2017-03-23T15:21:52Z")
For **Flyer** and others who cannot make the trip … my advice is to be patient if you’re young … there will be other total solar eclipses in the not-so-distant future … April 8th, 2024 – Central USA August 23rd, 2044 – Montana, N. Dakota August 12th, 2045 – Southern USA March 30th, 2052 – USA Noteworthy is that the first and fourth in the list above have duration twice as long, and the third in the list is _thrice_ as long … so this upcoming eclipse is nowhere close to being an opportunity of a lifetime … in fact, in a lousy 28 years we’ll have a better eclipse than this one at 6 minutes duration … One thing that isn’t mentioned in all the hysteria is that the very best visuals is when a total solar eclipse occurs much closer to solar maxima … and all these eclipses I’ve mentioned are all closer to solar minima … [sigh] … Anyway … my point is that these events are very uncommon … but not rare … I only recommend seeing one in your lifetime … you’ll have opportunities after this event … add it to your “bucket list” as it were … ---
**Author:** ![Bumbershoot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bumbershoot/32/3428_2.png) [@Bumbershoot](https://boards.straightdope.com/u/Bumbershoot)\ **Post date:** [March 23, 2017, 3:22pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/70 "2017-03-23T15:22:16Z")
Okay, further research seems to indicate that anyone between the two red lines on Jubier’s map will experience totality. The closer they are to the blue line, the longer totality will last. So Dave’s backyard should be just fine, as Darren Garrison said. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [March 23, 2017, 3:30pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/71 "2017-03-23T15:30:48Z")
> [@Bumbershoot](#): > > Okay, further research seems to indicate that anyone between the two red lines on Jubier’s map will experience totality. The closer they are to the blue line, the longer totality will last. So Dave’s backyard should be just fine, as Darren Garrison said. Ah, mea cupla. I misread your post (or read too rapidly really) and didn’t register “umbral depth” as the figure of merit. Yeah, no reason at all to move from the comfort of the back yard. The point about the distance I wrote above is all about the red line on the edge, not the middle of the path. ---
**Author:** ![Bumbershoot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bumbershoot/32/3428_2.png) [@Bumbershoot](https://boards.straightdope.com/u/Bumbershoot)\ **Post date:** [March 23, 2017, 3:43pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/72 "2017-03-23T15:43:00Z")
> [@Francis\_Vaughan](#): > > Ah, mea cupla. I misread your post (or read too rapidly really) and didn’t register “umbral depth” as the figure of merit. Yeah, no reason at all to move from the comfort of the back yard. The point about the distance I wrote above is all about the red line on the edge, not the middle of the path. No problem. I didn’t actually call it the blue line in my first post, I just said the line of totality and that could be the red line- it’s the outer edge of totality. Edit: So umbral depth and % of totality are not the same thing? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 23, 2017, 3:45pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/73 "2017-03-23T15:45:08Z")
> [@Bumbershoot](#): > > Would it be worth it for us to move 750 feet down the road and set up the cameras or can we get the same results from Dave’s backyard? Jubier’s map lists an Umbral depth of 99.6% for Dave’s backyard. Does that mean just 750 feet north of the line is 99.6% of totality? Playing around with the map more myself. It would be a less than 40 mile drive from the very outer edge of totality to the center, where you will get the maximum time of totality. Well worth it for, I would think, even if you do loose the convenience of being on your friend’s property. Earlier I said I was around 10 km from the center of the path of totality–that was estimating from the scale bar at the bottom of the map, I hadn’t noticed that the data box gives a number for that. I am 5.6 miles from the center of the path. My time of totality is 2 minutes, 34 seconds as opposed to 2 minutes, 38 seconds at the center. So that should give a very rough estimate that you lose 1 second of totality every 1.4 miles you are away from the center. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 23, 2017, 4:01pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/74 "2017-03-23T16:01:32Z")
> [@Darren\_Garrison](#): > > I don’t know the exact width of the path of totality of this eclipse, but think in the range of tens of miles (but less than hundreds.) So 750 feet will make essentially jack squat difference. Not true if those 750 feet are the difference between seeing totality and none. And even if you are a few feet inside the path of totality, that close to the edge it will be very short (also, the calculations may not be exact: refraction, your exact altitude, and the shape of the lunar limb need to be taken into account). To be on the safe side I would try to be at least a mile inside the published zone of totality. A 99.6% eclipse is still not very impressive. Edit: and I see that you were actually talking about the centre line. So no need to move at all! > [@Darren Garrison](#): > > My time of totality is 2 minutes, 34 seconds as opposed to 2 minutes, 38 seconds at the center. So that should give a very rough estimate that you lose 1 second of totality every 1.4 miles you are away from the center. It doesn’t work like that - the duration is pretty similar over most of the width of the path, and drops off rapidly towards the edges. You can click around in the Google Maps of the path on the Espenak site and it will give you the duration in any given spot. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 23, 2017, 4:09pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/75 "2017-03-23T16:09:16Z")
> [@Bumbershoot](#): > > I was playing around with Jubier’s map and just 95 feet north or south of the blue line gives an umbral depth of 99.95%. Does that mean that three people, one standing directly on the blue line and the other two 95 feet north and south of person #1 will have different experiences? The blue line is that precise? “Umbral depth” is really just an artificial measure of how near the centre line you are. It is not the same thing as “magnitude of eclipse”. From [Total Solar Eclipse Local Circumstances](https://eclipse.gsfc.nasa.gov/SEmono/reference/locircT.html) > [@](#): > > Two additional columns are included if the location lies within the path of the Moon’s umbral shadow. The umbral depth is a relative measure of a location’s position with respect to the central line and path limits. It is a unitless parameter which is defined as: > > u = 1 - abs(x/R) [1] > where: > > u = umbral depth > x = perpendicular distance from the shadow axis (kilometers) > R = radius of the umbral shadow as it intersects Earth’s surface (kilometers) > The umbral depth for a location varies from 0.0 to 1.0. A position at the path limits corresponds to a value of 0.0 while a position on the central line has a value of 1.0. The parameter can be used to quickly determine the corresponding center line duration. Thus, it is a useful tool for evaluating the trade-off in duration of a location’s position relative to the central line. Using the location’s duration and umbral depth, the center line duration is calculated as: > > D = d/(1 - (1 - u)2)1/2 seconds [2] > where: > > D = duration of totality on the central line (seconds) > d = duration of totality at location (seconds) > u = umbral depth > The final column gives the duration of totality. The effects of refraction have not been included in these calculations, nor have there been any corrections for center of figure or the lunar limb profile. Don’t worry about being close to the point of maximum eclipse or close to the centre line. As long as you are comfortably inside the path of totality, the only thing to concern yourself with is the weather forecast 🆒 ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 23, 2017, 4:14pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/76 "2017-03-23T16:14:48Z")
> [@Colophon](#): > > It doesn’t work like that - the duration is pretty similar over most of the width of the path, and drops off rapidly towards the edges. Yeah, you’re right–I instantly saw my error as soon as I saw mention that it was one. It wouldn’t fall off evenly, but as of a chord of a circle(ish.) ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [March 23, 2017, 4:21pm UTC](https://boards.straightdope.com/t/solar-eclipses-partial-vs-totality/782593/77 "2017-03-23T16:21:22Z")
What about Baily’s beads, how far off the center line does one need to be, generally? > [@Colophon](#): > > You can click around in the Google Maps of the path on the Espenak site and it will give you the duration in any given spot. “Espenak” – had to look that up, thanks for mentioning about Fred Espenak. So both he an Xavier Jubier have eclipse maps using Google Maps. Map, Fred Espenak – red center line, and blue lines define the bounds of totality: > **[NASA - Total Solar Eclipse of 2017 Aug 21](https://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html)** > > This page is part of the NASA Eclipse Website. > It uses Google Maps to create an interactive map of the > \