Umbrella

[Kenneth Spackman]

Hi all

I would like to ask some advice in regards to using an umbrella to stave off dew when star gazing. I read a article reporting up to 10 degree higher then the serounding area. This sounds to good to be true or is it. Does anyone use an umbrella to help stave off dew. I can see the benefits of umbrella as a shield for the wind. 

[bosun21]

I'll stick to a dew shield. I've seen umbrellas used in daytime to shield the scope from direct sunlight but never heard of them being used at night.

[Kenneth Spackman]

Hi bosun21

It is recommended under the heading: sky and telescope on Internet and umbrella is recommended as a shield against low temperatures. I am still a little dubious as I have not seen any one using umbrella to sheild telescope and equipment. 

[PeterStudz]

I think you mean this article…

https://skyandtelescope.org/astronomy-equipment/equipment-diy/dealing-with-dew/

”Then there's the observing umbrella, not a widely known accessory but one that works. A beach umbrella blocks the chill of outer space the same way it blocks the heat of the Sun. It can help shield all your gear and you too from the cosmic deep freeze. On a still night a thermometer under an umbrella can read more than 10° Fahrenheit (6° Celsius) higher than when it is exposed to the open sky.”

I’ve never tried. But in my younger days I’d go wild camping and sometimes use a tarpaulin (open on all sides) in order to keep dew off. 

[bomberbaz]

4 hours ago, Kenneth Spackman said:

Hi all

I would like to ask some advice in regards to using an umbrella to stave off dew when star gazing. I read a article reporting up to 10 degree higher then the serounding area. This sounds to good to be true or is it. Does anyone use an umbrella to help stave off dew. I can see the benefits of umbrella as a shield for the wind. 

I can also see the disadvantages of a potential wind catching, equipment smasher, just saying.

[ollypenrice]

Interesting.  In our robotic shed we have found that any kind of little 'roof' placed over a piece of equipment keeps dew off it. We now make little doll's house covers to put above above everything electronic. Some of the effectiveness of this will arise from the heat of the items in use but even when they have been switched off for days, in long spells of wet and humid weather, the items beneath them stay dry when the 'roofs' are wet.

Olly

[PeterStudz]

I’ve got one of those large patio parasols. It’s wind resistant too, although for me heavy dew nights have been when it’s calm anyway. 

I might put it up one night and see how it goes. As long as it doesn’t get in the way I can’t see it’ll case a problem. 

[Kenneth Spackman]

Hi peterstudz. 

I have given this more thought. I have done a lot of camping over the years and have left doors and roof partial open and the dew has been quite bad outside but not inside the tent also, I have noticed that dew never enters my shed. I also used to do a lot of night fishing under an open fishing umbrella and come to think about it, never got dew on my equipment. I have a large patio umbrella and will definitely give it a try. 

[JeremyS]

This is one reason I chose a domed obsy. Sitting inside, at my computer imaging, most of the time there is some dome over my head. This reduces heat radiation to the sky, making me feel not so cold. If my head were metal or glass, the cooling could result in dewing

[jjohnson3803]

I've seen more and more people pitch tents under large pop-up canopies and leave their rainflies off.  I assume that's to limit dew and allow better circulation, so it seems an umbrella could work.  I'd also think you could use a canopy for observing as long as it's not obstructing your line of sight.  Amazon US sells a 5ft x 7ft canopy that I might try.

 

 

[Kenneth Spackman]

Hi JJonson

I am just awaiting clear nights and will try out the large patio umbrella I have. I will also try the thermonitor test and will report back with results. Might be a while as next ten nights cloudy. 

[Louis D]

On 27/07/2023 at 15:20, PeterStudz said:

I think you mean this article…

https://skyandtelescope.org/astronomy-equipment/equipment-diy/dealing-with-dew/

”Then there's the observing umbrella, not a widely known accessory but one that works. A beach umbrella blocks the chill of outer space the same way it blocks the heat of the Sun. It can help shield all your gear and you too from the cosmic deep freeze. On a still night a thermometer under an umbrella can read more than 10° Fahrenheit (6° Celsius) higher than when it is exposed to the open sky.”

I’ve never tried. But in my younger days I’d go wild camping and sometimes use a tarpaulin (open on all sides) in order to keep dew off. 

This article goes on to say the following:

You can take active countermeasures too. A 4- or 7-watt light bulb inserted into a blanketed telescope makes a nice low-power heater. 

Well, the article should probably be updated from its original 2006 published version to specify a 4 W incandescent light bulb because I've got a modern 4 W LED light bulb that is a 40 W incandescent lumen equivalent that emits no infrared radiation, which is I think the form of heating the article desires.  It does emit waste heat from the LED itself, but that is mostly confined to the base and would eventually reradiate as far infrared radiation.  However, an LED light bulb is less efficient at immediately converting electricity purely to heat than an incandescent light bulb because it is optimized to convert electricity into visible light that doesn't warm things very quickly.  I suppose the visible light photons, if contained within a light tight enclosure, would eventually warm whatever they strike in there, so an LED light bulb still might be 100% efficient at converting electricity to heat in the long run.

Edited July 29, 2023 by Louis D

[Mandy D]

6 hours ago, Louis D said:

This article goes on to say the following:

You can take active countermeasures too. A 4- or 7-watt light bulb inserted into a blanketed telescope makes a nice low-power heater. 

Well, the article should probably be updated from its original 2006 published version to specify a 4 W incandescent light bulb because I've got a modern 4 W LED light bulb that is a 40 W incandescent lumen equivalent that emits no infrared radiation, which is I think the form of heating the article desires.  It does emit waste heat from the LED itself, but that is mostly confined to the base and would eventually reradiate as far infrared radiation.  However, an LED light bulb is less efficient at immediately converting electricity purely to heat than an incandescent light bulb because it is optimized to convert electricity into visible light that doesn't warm things very quickly.  I suppose the visible light photons, if contained within a light tight enclosure, would eventually warm whatever they strike in there, so an LED light bulb still might be 100% efficient at converting electricity to heat in the long run.

Absolutely, 100%, if contained, all the radiation from any source will ultimately be converted to heat. Makes no difference whether it is an LED or a filament lamp. How well the different wavelengths are absorbed by the various surfaces is a different matter, but it will all end up as long wavelength infra-red eventually.