# How many Galaxies blocked by my fingernail **URL:** \ **Category:** Factual Questions\ **Created:** [November 11, 2019, 6:22pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297 "2019-11-11T18:22:43Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [November 13, 2019, 1:08am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/41 "2019-11-13T01:08:42Z")
> [@panache45](#): > > And just think, that light traveled billions of years unimpeded, only to be stopped by your thumb. Or, if visible, by the retina of your eye. And if you had blinked, its multi-billion-light-year journey would have been in vain. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 13, 2019, 1:31am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/42 "2019-11-13T01:31:35Z")
> [@](#): > > Fine – think of it as an analogy, then. Our universe, as best as we can tell, behaves in a way consistent with space expanding in this way. And it’s also, as best as we can tell, consistent with models that are completely, utterly different from that. In other words, we have no clue. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [November 13, 2019, 2:04pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/43 "2019-11-13T14:04:38Z")
> [@Andy\_L](#): > > Why? Because degrees near the poles of the sphere are smaller than degrees near the equator (one foot near the pole may cover dozens or hundreds of degrees). Oh, I see what you’re getting at. Ignorance fought! ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 13, 2019, 2:41pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/44 "2019-11-13T14:41:00Z")
> [@bump](#): > > Oh, I see what you’re getting at. Ignorance fought! Glad to help ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [November 13, 2019, 3:20pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/45 "2019-11-13T15:20:13Z")
Just as a contrast to the Hubble Deep Field image, there is the [Boötes void](https://en.wikipedia.org/wiki/Bo%C3%B6tes_void). In an area that should have about 2000 galaxies, there are 60. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [November 13, 2019, 3:42pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/46 "2019-11-13T15:42:46Z")
> [@Babale](#): > > That’s all true, but keep in mind, we’ve never sent a probe that was actually intended to be interstellar. The ones that HAVE “left” the solar system (they’re still in the Oort cloud I believe) \ Voyager 1 has passed through the Kuiper belt more or less (the boundary is fuzzy) but the outermost part of the Kuiper belt is [less than a thousandth](https://www.spacetelescope.org/images/opo0204i/) of the way to the Oort cloud. All the hulabaloo last year about Voyager _2_ [entering interstellar space](https://voyager.jpl.nasa.gov/news/details.php?article_id=112) was because it had crossed the heliopause. ---
**Author:** ![TreacherousCretin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/treacherouscretin/32/476_2.png) [@TreacherousCretin](https://boards.straightdope.com/u/TreacherousCretin)\ **Post date:** [November 13, 2019, 6:33pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/47 "2019-11-13T18:33:00Z")
> [@Ike\_Witt](#): > > Just as a contrast to the Hubble Deep Field image, there is the [Boötes void](https://en.wikipedia.org/wiki/Bo%C3%B6tes_void). In an area that should have about 2000 galaxies, there are 60. Cool. I’ve wondered about such spots. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [November 13, 2019, 7:26pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/48 "2019-11-13T19:26:53Z")
We cannot begin to answer the OP’s question quantitatively unless we know the precise dimensions of the fingernail in question. [This person](https://cdnph.upi.com/svc/sv/i/2911479481885/2016/1/14794833297074/Texas-woman-attempts-to-grow-worlds-longest-nails.jpg) might be able to blot out the entire universe. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 13, 2019, 7:44pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/49 "2019-11-13T19:44:14Z")
> [@Ike\_Witt](#): > > Just as a contrast to the Hubble Deep Field image, there is the [Boötes void](https://en.wikipedia.org/wiki/Bo%C3%B6tes_void). In an area that should have about 2000 galaxies, there are 60. Sorry, but this is not in contrast to the Hubble Ultra Deep Field. As your cite tells us, the diameter of the Boötes void is only 330 million ly, or 0.27% the diameter of the observable universe, which is a very small fraction of the depth of the Ultra Deep Field. That means that if someone did an Ultra Deep Field in the middle of that void, it would look about the same as the actual HUDF. The main difference would be somewhat fewer foreground galaxies. As pointed out upthread, these voids and dense clusters average out when you combine everything out to the edge of the observable universe. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [November 13, 2019, 11:52pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/50 "2019-11-13T23:52:41Z")
> [@dtilque](#): > > Sorry, but this is not in contrast to the Hubble Ultra Deep Field. As your cite tells us, the diameter of the Boötes void is only 330 million ly, or 0.27% the diameter of the observable universe, which is a very small fraction of the depth of the Ultra Deep Field. That means that if someone did an Ultra Deep Field in the middle of that void, it would look about the same as the actual HUDF. The main difference would be somewhat fewer foreground galaxies. > > As pointed out upthread, these voids and dense clusters average out when you combine everything out to the edge of the observable universe. I’m getting confused. Does this square with the known [distribution of galaxies](http://tdc-www.harvard.edu/zcat/) which seem to suggest very substantial voids? Or are you saying that Geller et al didn’t look deep enough? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 14, 2019, 2:23am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/51 "2019-11-14T02:23:38Z")
> [@KarlGauss](#): > > I’m getting confused. Does this square with the known [distribution of galaxies](http://tdc-www.harvard.edu/zcat/) which seem to suggest very substantial voids? Or are you saying that Geller et al didn’t look deep enough? There are voids and concentrations or galaxies. Size-wise they’re 3 or more orders of magnitude smaller than the observable universe. So looking in any direction will mean you’re probably looking through 1000 or more voids and clusters. (Well, OK, as long as you don’t look where there’s some foreground obstruction, such as the [Zone of Avoidance](https://en.wikipedia.org/wiki/Zone_of_Avoidance).) Anyway the voids and dense clusters will average to about the same number of galaxies in any direction. ---
**Author:** ![TreacherousCretin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/treacherouscretin/32/476_2.png) [@TreacherousCretin](https://boards.straightdope.com/u/TreacherousCretin)\ **Post date:** [November 14, 2019, 3:06am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/52 "2019-11-14T03:06:27Z")
> [@dtilque](#): > > Sorry, but this is not in contrast to the Hubble Ultra Deep Field. As your cite tells us, the diameter of the Boötes void is only 330 million ly, or 0.27% the diameter of the observable universe, which is a very small fraction of the depth of the Ultra Deep Field. That means that if someone did an Ultra Deep Field in the middle of that void, it would look about the same as the actual HUDF. The main difference would be somewhat fewer foreground galaxies. > > As pointed out upthread, these voids and dense clusters average out when you combine everything out to the edge of the observable universe. You’re right. I should have read the description more carefully. ---
**Author:** ![Nansbread1](https://avatars.discourse-cdn.com/v4/letter/n/6a8cbe/32.png) [@Nansbread1](https://boards.straightdope.com/u/Nansbread1)\ **Post date:** [November 14, 2019, 11:42am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/53 "2019-11-14T11:42:57Z")
> [@Northern\_Piper](#): > > This was a really interesting OP. Simple, yet it triggered such an interesting discussion. Well thank you. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [November 14, 2019, 6:42pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/54 "2019-11-14T18:42:30Z")
> [@Andy\_L](#): > > Stand in the middle of a sphere big enough that one degree of arc from where you are looking is one foot in length. That means that the sphere has a circumference of 360 feet and thus a radius of 360/(2 pi) feet. The area of a sphere is 4 pi radius-squared, which equals (for this case) 360\*360/pi square feet - or 41,252 square feet. Since one degree across is one foot, the sphere covers a solid angle of 41,2521 square degrees. > > Why? Because degrees near the poles of the sphere are smaller than degrees near the equator (one foot near the pole may cover dozens or hundreds of degrees). Would polar coordinates extended into three dimensions not be the right unit to avoid that problem? You should measure those degrees from the center of the Earth (which would be confusingly called a _pole_) in radians. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 14, 2019, 8:25pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/55 "2019-11-14T20:25:05Z")
Still doesn’t help, because spherical coordinates still have a pole along the z axis. They’re basically just latitude and longitude, combined with height. What you can use are r, longitude, and sine of latitude. ---
**Author:** ![Regallag\_The\_Axe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/regallag_the_axe/32/445_2.png) [@Regallag\_The\_Axe](https://boards.straightdope.com/u/Regallag_The_Axe)\ **Post date:** [November 14, 2019, 9:35pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/56 "2019-11-14T21:35:44Z")
> [@Wendell\_Wagner](#): > > A thumbnail is about 1.5 degrees in width at arm’s length. A thumbnail takes up probably about one-hundred-thousandth of the sphere around your eye at arm’s length. There are at least 2 trillion galaxies in the observable universe, so there are about 20 million galaxies covered up by your thumbnail at arm’s length from the point of view of your eye. Please correct me if this is my ignorance speaking, but if the observer were standing on the surface of the Earth wouldn’t they have only _half_ of the galaxies in the observable universe in their field of vision? The rest would be blocked by the the Earth itself, so any calculation should only take half of the observable galaxies as one of its values, right? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 14, 2019, 11:12pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/57 "2019-11-14T23:12:32Z")
That’s relevant for how many you’d see, but not for how many your thumb would block. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 15, 2019, 3:53am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/58 "2019-11-15T03:53:12Z")
> [@Pardel-Lux](#): > > Would polar coordinates extended into three dimensions not be the right unit to avoid that problem? You should measure those degrees from the center of the Earth (which would be confusingly called a _pole_) in radians. Unfortunately not. Consider a one degree wide strip of a sphere, near the sphere’s north pole. If you naively calculate the area of that strip you’d get 1 degree wide by 360 degrees long - just the same as the area of a strip at the equator. But the strip at the equator has a much bigger area, in units of square feet, square meters or square degrees (or the proper unit, steradians) ---
**Author:** ![MarvinKitFox](https://avatars.discourse-cdn.com/v4/letter/m/7ba0ec/32.png) [@MarvinKitFox](https://boards.straightdope.com/u/MarvinKitFox)\ **Post date:** [November 15, 2019, 7:02am UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/59 "2019-11-15T07:02:15Z")
> [@glee](#): > > Are you saying the distant galaxies are receding from us at greater than the speed of light? > > I thought only massless objects could travel that fast… not “moving away” exactly, just “getting further away” It’s more a case of more space appearing inbetween, than it is a case of moveing at speed through existing space. This is why the universe can be 93 billion light years across, despite starting as a point source only 13.8 billion years ago. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [November 15, 2019, 1:17pm UTC](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297/60 "2019-11-15T13:17:30Z")
> [@Chronos](#): > > Still doesn’t help, because spherical coordinates still have a pole along the z axis. They’re basically just latitude and longitude, combined with height. > > What you can use are r, longitude, and sine of latitude. I did not write spherical coordinates, but polar coordinates extended in three dimensions. There is no north pole there. > [@Andy\_L](#): > > Unfortunately not. Consider a one degree wide strip of a sphere, near the sphere’s north pole. If you naively calculate the area of that strip you’d get 1 degree wide by 360 degrees long - just the same as the area of a strip at the equator. But the strip at the equator has a much bigger area, in units of square feet, square meters or square degrees (or the proper unit, steradians) I insist: you should not take a ring between any two latitudes that will obviously be bigger close to the equator than close to the pole, but the maximum circle, which is always equal, as a reference. Every step should be a 1/nth (n being arbitrarily small) of a radian and should be the same area variation, step by step, close to the equator or close to the pole. In fact, there is no pole in polar coordinates other than the point (0, 0, 0), where the system gets its name from. [Previous page](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297.md?page=2) [Next page](https://boards.straightdope.com/t/how-many-galaxies-blocked-by-my-fingernail/843297.md?page=4)