Observing the sky through a professional telescope is one of those dreams many of us have since childhood, but for a night of observation to be perfect, having good instruments is not enough: weather and observation time management at astronomical observatories They are as important as the telescope itself. Clouds, wind, turbulence, and even jet streams can ruin in minutes what takes months to plan.
In Spain we have some of the most prestigious observation sites in the world and a very finely tuned network of meteorological and forecasting services. Understanding how observation time is allocated, what weather conditions are monitored, and what tools are available to predict them It is key for both the scientific community and amateur astronomers who want to make the most of every clear night.
Observation time at Spanish observatories
One of the major driving forces behind astrophysics in our country is the Canary Islands Institute of Astrophysics (IAC), whose main mission is to promote world-class astrophysical researchOne of the most powerful ways to achieve this is to facilitate access for the Spanish scientific community to the observation time available on the telescopes of the large observatories located in the Canary Islands.
In Spanish territory, two enclaves stand out in particular: the Roque de los Muchachos Observatory, in La Palma, and the Teide Observatory, in TenerifeBoth are part of the so-called Canary Islands Observatories and house telescopes from multiple international institutions, with specific agreements that regulate what percentage of time corresponds to Spain and how it is divided among different scientific projects.
The allocation of observation time to the Spanish community is not done randomly or arbitrarily: It is structured through several formal channelsDepending on the telescope, the type of observation (solar or night) and the scientific agreements signed with the owners of each facility.
Much of that distribution is centralized through the Time Allocation Commission (CAT)The Canary Islands Telescope Array (CAT) is an organization that coordinates access to a large number of telescopes located at observatories in the Canary Islands. The CAT is structured into two distinct committees: the Solar Committee, which handles solar observation projects, and the Night Committee, which evaluates requests for night sky observations.
The members of this committee are not administrative staff or general managers: These are astrophysicists with extensive scientific qualifications.They are linked to universities, institutes, and research centers, both national and international. They analyze the proposals, assess their scientific quality, and decide which projects receive observation time and with what priority.
According to the international cooperation agreements in astrophysics signed with the owners of the telescopes, The CAT manages approximately 20% of the observation time allocated to Spain.This time is distributed among carefully selected, competitive projects to ensure that telescope hours are used to their fullest potential in high-impact research.
In the specific case of the Teide Observatory, some telescopes have a different management dynamic. Instruments such as the IAC80, the TCS (Carlos Sánchez Telescope) or the OGS (Optical Ground Station) They are under the responsibility of the Head of the Telescope Operations Group. This person directly reviews and evaluates the observation proposals submitted for these facilities, seeking a balance between internal IAC projects and external collaborations.
In addition to the locally managed telescopes, the community linked to the IAC enjoys specific access to other telescope networks spread across the planet, such as SARA (Southeastern Association for Research in Astronomy) or LCOGC (Las Cumbres Observatory Network). These agreements greatly expand the observation window, allowing coverage of different wavelengths and time slots that are not always accessible from the Canary Islands.
The Calar Alto Observatory and its observation conditions
Another of the great figures in professional astronomy in Spain is the Hispanic Astronomical Center in Andalusia (CAHA), known worldwide as the Calar Alto Observatory. This scientific complex is located in the Sierra de Filabres mountain range, in the province of Almería, on a plateau at an altitude of approximately 2168 meters, a privileged environment for observing the Universe.
The origin of this observatory dates back to 1973, the result of a collaboration agreement between the governments of Germany and SpainSince then, it has established itself as one of the pillars of European astrophysics, with a long tradition of cutting-edge projects and large-scale observation campaigns.
Its facilities include several telescopes with different apertures and optical designs, adapted to multiple types of studies. The most outstanding is the 3,5-meter diameter telescope, long considered the largest optical telescope in continental Europe, which has allowed it to lead deep observations of galaxies, star clusters and other distant objects.
Since 2019, the management of CAHA has been the responsibility of Institute of Astrophysics of Andalusia (IAA-CSIC) and the Regional Government of Andalusiawhich operate it jointly. This combination has strengthened both the international scientific aspect and the role of the observatory in the Andalusian and Spanish research ecosystem.
In Calar Alto, projects are developed in very diverse fields: exoplanet search, detailed studies of star formation, analysis of galaxy structure, or cosmological research on the expansion of the universe and the large-scale distribution of matter. For all of them, having a stable and well-characterized sky is as crucial as the technological equipment itself.
What is a weather observatory and why is it so important?
When we talk about “time at astronomical observatories” we are not only referring to how many hours of telescope time are available, but also to the weather conditions that determine whether a night is suitable for observationMeteorological observatories come into play to measure and monitor these factors.
A meteorological observatory is, in essence, a place dedicated to evaluating atmospheric conditions in real timeIt is equipped with specific instrumentation to record parameters such as temperature, humidity, pressure, wind speed and direction, cloud type and quantity, visibility, and precipitation.
In addition to automatic sensors, there are usually specialized personnel who make direct observationsThis includes both sensory data (sky conditions, presence of phenomena such as fog, storms, etc.) and instrumental data (precise equipment readings). In many astronomical observatories, meteorological information is continuously recorded and shared with astronomers to plan the night.
Without this data, organizing an observation campaign would be practically a lottery. Precision astronomy requires knowing in advance whether the sky will be clear, how stable the atmosphere will be, or if there is a risk of rain or ice. that could damage the domes and telescopes. Hence, meteorology applied to astronomy is almost a discipline in itself.
In addition to the stations installed at the observatories themselves, official agencies and forecasting websites make information available to the public. detailed and up-to-date weather information which is very useful for amateur and professional astronomers who want to prepare their observation sessions at home or in the field.
The importance of weather forecasting for the amateur astronomer
Therefore, among the basic routines of any advanced amateur is Check the weather forecast for your observation area or the place you plan to travel to. It's no longer enough to look out the window or rely on a general forecast: you need to know in some detail the expected behavior of the clouds, the seeing, the wind, and other fine parameters.
There are specialized websites that keep the real-time weather situationdisplaying the most relevant parameters: cloud cover, rain, temperature, humidity, and wind, among others. These types of tools allow you to decide whether it's worth setting up all the equipment or if it's better to leave it for another night.
Among the resources most valued by the community are the satellite maps with cloud cover and rain radars, which allow you to see at a glance how cloud masses are evolving and whether a storm is approaching or moving away from your area. For mobile observation sessions and for outings to see meteor showersThey are almost indispensable.
In addition, many specialized sites offer layered views, time-based animations, or even very short-term cloud cover predictionsThis is especially useful when traveling several kilometers in search of darker skies and needing to know if there will be a window of several hours of clear skies.
Key meteorological tools for astronomical observation
In Spain, one of the reference sources is the State Meteorological Agency (AEMET), which brings together on its website a huge amount of information: maps of rain, cloud cover, wind, warnings for adverse phenomena, satellite images and real-time observation data from many stations spread throughout the territory.
Within AEMET there is a specific section on real-time observation It offers direct readings of temperature, wind, significant weather phenomena, and other parameters. This information, combined with its hourly forecasts and cloud and precipitation maps, helps to get a fairly reliable idea of how the sky will evolve overnight.
Another widely used website is The time isIt presents meteorological information in a highly visual way: short- and medium-term forecast models, interactive maps, and specific cloud and rainfall layers. For astronomers, the most interesting features are precisely these cloud cover and precipitation maps, which allow them to "play" with zoom and animation to track the evolution of air masses.
If you're looking for something even more focused on sky observation, it's usually recommended Sat24This website displays high-resolution satellite images in both the visible and infrared spectrum. One of its major advantages is its refresh rate: approximately The images are updated every 15 minutes.so that the movement of cloud fronts can be followed in considerable detail.
The clarity of these images, especially in visible mode during the day and in infrared at night, leads many enthusiasts to consider Sat24 one of the best options for knowing the cloud cover in the very short termWhen you're trying to determine whether a clearing will hold or if a band of high clouds will sneak in right at the time of the object you're interested in, this precision makes all the difference.
In the field of more detailed predictions, one of the services preferred by the astronomical community is meteoblueThis platform offers very detailed forecasts for the next three days, with the possibility of configuring them for specific locations, whether it be our home, a regular observation point, or a professional observatory.
What distinguishes Meteoblue from other general websites is that It includes parameters specifically designed for astronomy.It not only indicates cloud cover by layers, but also seeing indices, information on the jet stream and other data related to atmospheric stability, making it a reference tool for planning demanding nights of observation.
Most useful meteorological parameters for observing the sky
Within Meteoblue and other similar services, there are a number of variables that astronomers always look at with a magnifying glass. The “Time (CET)” columnFor example, it shows the time in Central European Time, which is the same time zone we use in mainland Spain and the Balearic Islands for most of the year. This makes reading the tables much easier, because the times shown coincide with our local time, avoiding confusion with conversions.
Cloud cover is usually divided into High, Mid and Low cloudsThat is, high, medium, and low clouds. For each type, a percentage of sky coverage is given: a value of 0 indicates that that type of cloud is not expected, while 100 means that the entire sky would be covered by that specific layer. By adding the information from all three, we can deduce whether we will have a completely clear sky or a mixture of clouds of different altitudes.
For amateur cyclists, high clouds are especially treacherous: Although they allow you to see some stars, they reduce contrast and hinder the observation of faint objects.Low and medium clouds, on the other hand, usually completely block the view of the sky, although sometimes they leave intermittent clearings that can be used in deep sky photography if one has patience.
Another key indicator in astronomy is the Seeing indexwhich appears in Meteoblue as Seeing Index 1 and 2. These are scales ranging from 1 (very poor conditions) to 5 (excellent conditions). Seeing summarizes the stability of the atmosphere in a single number: a low value implies a lot of turbulence and "shaky" stars, while a high value indicates that the atmosphere is relatively calm and very fine details can be seen on planets, the Moon, or double stars.
It is important to keep in mind that the seeing It does not take into account the presence of cloudsIt is an indicator of how light is distorted as it passes through different layers of air, regardless of how cloudy the sky is. Therefore, it's possible to have excellent seeing on a completely overcast night, something very frustrating but common for observers.
Among the variables that are least discussed but have the greatest influence is the jetstreamor jet stream. These are very fast-moving air currents located at high levels of the atmosphere. An intermediate level of jet stream is usually associated with relatively good seeing, because the flow helps to stabilize certain layers of air without generating excessive turbulence.
Instead, Very low jet stream values tend to favor the accumulation of high cloudswhich can ruin a night that, in principle, held great promise. Conversely, when the jet stream is too strong, the atmosphere is so agitated that the seeing degrades noticeably, greatly reducing the sharpness of images in high-magnification telescopes.
All these meteorological parameters are added to other more classic ones (surface wind, relative humidity, risk of rain, temperature and dew point) that They also affect both observer comfort and equipment safetyHigh humidity and low temperatures, for example, favor condensation on lenses and cameras, while strong gusts of wind may force domes to be closed or tripods to be folded to avoid damage.
Limitations and reliability of predictions
However sophisticated the models may be, Weather forecasts are never infallibleServices such as AEMET, ElTiempo.es, Sat24 or Meteoblue combine real observations with computer simulations, but the atmosphere is a chaotic system and small variations can change the results with only a few hours' notice.
That's why many experienced observers use multiple sources of information in parallel They compare what each model says. If all the models agree on a clear night, it's usually the case; if there are serious discrepancies, it's best to be cautious, especially if it involves traveling far or transporting delicate equipment.
Another aspect to consider is the spatial and temporal resolution of each modelSome models work better in coastal areas, others in mountainous regions, and not all capture the local microclimates that affect specific valleys or plateaus equally well. For a fixed observatory with years of data, it's easier to learn how each model behaves and what biases it tends to have.
It should also not be forgotten that many weather websites, in order to function and improve their services, make use of own and third party cookiesThese are used, among other things, to collect anonymous usage data, better tailor content, and analyze traffic. Generally, if the user continues browsing, it is interpreted as acceptance of the use of cookies, although it is always possible to configure them from the browser itself.
Blocking these cookies completely may cause certain navigation difficultiessuch as the loss of saved preferences or the malfunction of some interactive modules. In any case, each user can adjust the privacy level to their liking, always with the advantage of accessing predictions that help them better plan their observation sessions.
For both professional and amateur observatories, the binomial observation time – atmospheric weather It's everything: on the one hand, you have to fight for observing time on cutting-edge telescopes through international commissions and agreements; on the other, you have to closely monitor what the atmosphere is doing to take advantage of every last minute of clear skies. The combination of good infrastructure, reliable meteorological tools, satellite megaconstellations And some personal experience makes the difference between a season of "postcard skies" and a year full of lost nights.