Calculating horizon angle

[RobH2020]

Hi all, 

I'm trying to work out if I'll be able to see Mars, Jupiter, Saturn from my garden this year. I'm south facing, so that should be OK... but I live in valley country, so I'm not sure if the opposite side of my valley means I won't be able to see them from here.

Any idea how to calculate what my horizon is, so I can compare with the maximum altitudes of the planets this year?

Thanks!
Rob

Edited June 23, 2020 by RobH2020

[kerrylewis]

Hello Rob

if you have a smartphone you can get various apps which measure angles. I have a couple of compass  apps which show elevation and you can see the horizon through them with the camera. If you have an iPhone I can give you specifics 

Kerry

[andrew s]

I think you will have to measure it. You could use a spirit level and a sighting arrangement with a protractor. Then use a planetarium program to see the altitude of the plants relative e to your measured horizon.

Regards Andrew 

PS or the high tech method just posted 🙄 it's  an age thing.

Edited June 23, 2020 by andrew s

[RobH2020]

Thanks all! Is it literally just the angle in degrees towards the horizon away from flat level (as measured by spirit level)? 

I can rig that up! Then the number that comes out of that is then on the same scale as those used for describing planetary max altitudes?

[andrew s]

7 minutes ago, RobH2020 said:

Thanks all! Is it literally just the angle in degrees towards the horizon away from flat level (as measured by spirit level)? 

I can rig that up! Then the number that comes out of that is then on the same scale as those used for describing planetary max altitudes?

Yes

[barkis]

Locate star that will transit your local meridian  at your intended observing date and time.  Look for the declination of same star, and compare it with that of the planets you wish to observe.

You could get a good idea if you will get a decent window of observing time, or otherwise be limited short sessions either side of your local north south line. Much could depend upon the height of your southern obstructions.

Ron.

Edited June 23, 2020 by barkis

[Tomatobro]

Compass, cheap angle finder and a guide scope with cross hairs.

[JOC]

Won't it be necessary to adjust the measured horizon relative to how high the OP is to begin with .  Surely the star measurements are taken relative to sea level horizon.  If the OP is in a Valley which is still 100m above sea level then does this need to be adjusted for.  For example in some instances you might be looking down to a horizon?   Either that or I've missed something huge in my thinking.

[Ruud]

Here's a tip for once you know your horizon. You can do some nice calculations.

This is Stellarium. The atmosphere is turned off and  the Astronomical calculations is open (F10). Mars is selected and both it and the Sun are graphed for altitudes above 0°.
For 23 June 2020, the graph suggests the best time to try for Mars would be around 4 AM, with Mars 20° above the horizon in the SE and the Sun still under the horizon.

 

With Astronomical calculations you can discovered some amazing things. For instance with the Phenomena tab: Jupiter and Saturn will be extremely close together on December 21st 2020. Unfortunately they'll be quite close to the Sun as well: at sunset the pair is only 14° above the SW horizon. (All this is for my location.)

In a telescope it will look like this:

The blue segment is from Stellarium's Angle Measurement plug-in. The separation is about 7 arc minutes. That's a quarter the size of the Moon.

The manual for Stellarium is in the folder ...\Program Files\Stellarium\guide (windows). There you can read what Astronomical Calculations can do and how the Angle Measurement plug-in works. Also try the plugin Observability Analysis.

Clear nights.

[andrew s]

12 minutes ago, JOC said:

Won't it be necessary to adjust the measured horizon relative to how high the OP is to begin with .  Surely the star measurements are taken relative to sea level horizon.  If the OP is in a Valley which is still 100m above sea level then does this need to be adjusted for.  For example in some instances you might be looking down to a horizon?   Either that or I've missed something huge in my thinking.

A planetarium program should use your Lat Long and height wrt sea level in its calculations.

Regards Andrew 

Edited June 23, 2020 by andrew s

[Skipper Billy]

Or you could create a photo realistic landscape in Stellarium then you can see at a glance if something is visible or not?

See attached - it tells me that at 0100 tonight Saturn will be briefly visible above my polytunnel - and it was last night - absolutely spot on. It also allows you to change the date and month so you can see what will be visible and when.

 

 

[RobH2020]

6 minutes ago, Skipper Billy said:

Or you could create a photo realistic landscape in Stellarium then you can see at a glance if something is visible or not?

See attached - it tells me that at 0100 tonight Saturn will be briefly visible above my polytunnel - and it was last night - absolutely spot on. It also allows you to change the date and month so you can see what will be visible and when.

 

 

That's great! May i ask how you did that? I'm afraid I'm only a beginner in Stellarium.

[RobH2020]

It basically looks as though by this time next month, Jupiter and Saturn will be about +15 degrees above the horizon by about midnight...

So I just have to work out whether my horizon is more or less than 15 degrees above my patio...

In any case they'll be quite low down... will they visible at that altitude in bright suburban light pollution do we know?

Edited June 23, 2020 by RobH2020

[RobH2020]

2 hours ago, Tomatobro said:

Compass, cheap angle finder and a guide scope with cross hairs.

 

That's a good bit of kit! Did you just use it for what we're talking about here, or you use it more generally too?

[Tomatobro]

5 minutes ago, RobH2020 said:

That's a good bit of kit! Did you just use it for what we're talking about here, or you use it more generally too?

When Tomato built his Pulsar dome we wanted to check the horizon profile which was the prime reason for knocking it together but the horizon picture is how my view looks from where I set up my scope.

Those digital angle finders are now about £13 and they have back illumination that wakes up when moved. Great for Alt/Az  mounts. The protractor is printed out using Blocklayer. Just type that into your search engine, set up the size and print it out

[RobH2020]

4 minutes ago, Tomatobro said:

When Tomato built his Pulsar dome we wanted to check the horizon profile which was the prime reason for knocking it together but the horizon picture is how my view looks from where I set up my scope.

Those digital angle finders are now about £13 and they have back illumination that wakes up when moved. Great for Alt/Az  mounts. The protractor is printed out using Blocklayer. Just type that into your search engine, set up the size and print it out

Excellent, thanks! Actually I can even just use my phone... My life was changed when I discovered the "angle meter" app 😉

[JOC]

23 hours ago, Tomatobro said:

Compass, cheap angle finder and a guide scope with cross hairs.

That won't account for altitude though will it?

[Waddensky]

PeakFinder is a great free resource to find out horizon elevation angles for specific locations, based on SRTM data.

Edited June 24, 2020 by Waddensky

[Waddensky]

23 hours ago, JOC said:

If the OP is in a Valley which is still 100m above sea level then does this need to be adjusted for.  For example in some instances you might be looking down to a horizon?

That's correct. For an elevated observer, the actual horizon angle can be less than 0. This Wikipedia article (header Zenith angle) has a figure explaining the geometrics.

[Tomatobro]

34 minutes ago, JOC said:

That won't account for altitude though will it?

Nor atmospheric distortion.......

[Skipper Billy]

On 23/06/2020 at 14:29, RobH2020 said:

That's great! May i ask how you did that? I'm afraid I'm only a beginner in Stellarium.

There are many videos on YouTube etc and this is a good 'how to'.

 

[JOC]

2 hours ago, KevS said:

Dependent upon the particular circumstance Saturn and Jupiter may be problematical but Mars is some 40 degrees at opposition in October so unless the Hertfordshire Matterhorn is in the way I don't envisage any problems.

LOL, I was also kind of looking at it from the persepctive of using the degrees up and down (and left to right, though that won't so affected) that are published for any given object.  If you have some form of marker on the telescope for vertical degrees and a reference says that Saturn is at 10 degrees altitude it won't be any good setting the marker on the telescope for 10 degrees if the telescope is already sitting hundreds of metres up.  There must be a standard adjustment that can be used, i.e. subtract 1 degree from the published figure for the object for every x metres the scope is sitting above sea level?

[RobH2020]

Thanks all - saw Jupiter last ngiht for the first time ever through my binoculars. Amazing!! All four moons. 

Can't wait to get my scope out tonight to have a much better look. I'm fingers crossed for cloud bands, great red spot etc.... (skywatcher 150 so should be able to!)