Frequently Asked Questions


When is the Observatory open?
The Observatory is open 365 days a year for the staff, and for pre-arranged visits, shopping or programs. For general tours and the gift shop we are open from 10 a.m. to 4 p.m. Saturdays and Monday holidays year round. We are open 10 to 4 Sundays from Presidents’ Day weekend in February through the last Sunday in December. Our observations will continue during the planned renovation to our facility from Summer 2021 to Spring 2022, though the building will be closed to the public during this time.
I have a disability. How can I access the Observatory?
The closest public parking to the Observatory is at the Trailside Museum at the base of Great Blue Hill. The pedestrian route from this parking lot to the observatory along the summit road is approximately one mile long, with an average slope of 15-20%. This road is not open to public vehicles. Special arrangements can be made for specific vehicles to drive to the Observatory. If you have concerns about reaching the Observatory, please contact us to arrange vehicular access to the top.

Blue Hill Observatory is over one hundred and thirty years old, and was built in several stages on top of the hard granite hilltop. The route up to the tower includes slopes up to 18% and rocky natural terrain. Once inside, many of our public rooms are accessible to guests with limited mobility, but there are some areas that can be reached only by steps, including the observation room in the tower. Many of the exhibits within the Observatory can be moved to accessible areas, and accommodations will be provided if you do not wish to or cannot travel to the upper rooms. The hilltop around the Observatory is rocky and uneven in many places, with steep slopes and abrupt changes in level. Accommodations will be provided if you do not wish to or if you are unable to navigate the hilltop.

Our staff is used to welcoming students and participants of all abilities to our programs. To request an accommodation, please contact Program Director Don McCasland at 617-696-0562 or

How do I become a member of the Blue Hill Observatory & Science Center or renew my membership?
Please visit our Membership page for all your options or call 617-696-0562 or e-mail
What is the best way to hike to the Observatory, and how long will it take?
The Service Road, located at the junction of Rt. 138 and Canton Avenue, is one mile long and takes about 20 minutes to hike. A slightly shorter, but somewhat rougher and steeper route, is the Red Dot trail, which starts from the Trailside Museum south parking lot. A lot of people like that route because it is a hike through the woods along a rocky trail, and it also takes 20 to 30 minutes for most people. We do offer guided hikes which last about one hour and can be for up to 30 people for a single hike. Longer hikes options are available on your own or with a guide.
May I drive up to the Observatory?
The Service Road is open to “authorized vehicles” only. Directions will be provided when you make arrangements for Service Road Access.
How do I make arrangements to drive up to the Observatory?
Please contact Program Director Don McCasland by phone at 617-696-0562 or by e-mail . You will get specific instructions for the date as well as for your group and vehicle(s).
Do Observatory members have to schedule a visit?
Though appreciated, that is not necessary during normal daytime operating hours. Just bring your member card, and if the main gift shop (back) entrance is locked, then go to the Staff/Volunteer (front) entrance. Simply knock on the door, walk in and call out “I am an Observatory member here for a visit”, and a staff member will greet you ASAP and will verify your member card.
I am a supporter of the Friends of the Blue Hills. Does that qualify me as an Observatory member?
The FBH is a good organization and we appreciate their support and advocacy for the entire Blue Hills Reservation, but they do not provide financial support to Blue Hill Observatory. If you would like to join the Friends of the Blue Hills, click on the link.
I am a member of Mass Audubon. Does that qualify me as an Observatory member?
Blue Hill Observatory has no affiliation with Mass Audubon and is not associated with the Blue Hill Trailside Museum. Your membership in Mass Audubon does not count as being an Observatory member. Please note: we do offer members of Mass Audubon, Friends of Blue Hills, WGBH, WERS, KONE, AKA a 10% discount in our Gift Shop and discounts on tour admission as a gesture of gratitude for your support of these organizations.
Does the Observatory provide daily weather forecasts?
The Observatory does not forecast the weather. That is the job of the National Weather Service and other meteorologists. We gather, record, and distribute weather data, some of which is provided to the National Weather Service as input to their computerized weather forecasting models. The climate data we provide helps broadcast meteorologists and others give perspective regarding weather events and allows us to monitor long-term climate changes and to educate the public about the climate.
Are there fees to access and to use the weather data?
The continuous data from the Automated Surface Observing System (ASOS) on Great Blue Hill (station ID KMQE) that is operated by the NWS is available on-line for free. It is also streamed to end users who subscribe to WSI or other weather information providers. Our Daily Discussion which is a summary of the prior full day and the manual observations at 7 AM, 10 AM and 1 PM (EST) is e-mailed to many meteorologists and atmospheric scientists and is also posted to our web site each day. Our 24 hour detailed data is available for a fee from BHOSC or other providers and can be read for free at the Observatory by members of BHOSC. Monthly and annual graphics and text summaries of the Blue Hill observations are also provided for free on our web site.
Who uses the weather data you collect?
The weather and climate data that we collect are provided to many users in a variety of ways, and it is used by Blue Hill staff for climate education and research. The data have been used in courtroom cases, for medical research, and in protecting our marine resources from contamination. Recently recognized by the World Meteorological Organization (WMO) as a Centennial Observing Station for its longevity and consistency, the Blue Hill Observatory provides climate data that are especially useful to researchers studying long term climate trends. Whereas “weather” is usually thought about in timeframes from one hour to two weeks, climate is usually measured in 30-year cycles.
Where do you get your funding?
Like most non-profits we get our funding from a variety of sources. The National Weather Service (NWS) underwrites a portion of our observing program. Other sources of funding include memberships, gift shop sales, foundation grants, and private and corporate donations.
How many different organizations have operated the Observatory?
Four different groups have run the daily weather observations since 1885. The founder, Abbott Lawrence Rotch, operated BHO privately from 1885 until 1912. Harvard College directed the Observatory from 1912 until 1959 when NOAA/National Weather Service took over operations until 1999. The non-profit Blue Hill Observatory & Science Center has run the observing and educational programs privately from 1999 to the present.
Who owns the Observatory?
The Observatory building has had three owners. Abbot Lawrence Rotch the founder, from 1885 until 1912, Harvard College from 1912 to 1971, and since 1971 the Commonwealth of Massachusetts has owned the Observatory, which is currently overseen as part of the Blue Hill Reservation by the Department of Conservation and Recreation (DCR).


What type of weather and climate data do you observe?
The Observatory has maintained an extensive and highly consistent record of weather observations continuously since February 1, 1885. Numerous weather parameters are recorded, including maximum and minimum temperature, precipitation, snowfall, snow depth, wind speed and direction, peak wind gust, surface pressure, dew point, relative humidity, water vapor pressure, sunshine duration, cloud cover, cloud type, visibility, and many others. Three complete manual observations are performed by the observer on duty each day at 7 AM, 10 AM and 1 PM Eastern Standard Time, and these are supplemented by continuous recordings of many parameters that allow us to record hourly data throughout the day.
Why does the Observatory used Eastern Standard Time year-round?
Although the biannual one-hour switch between Eastern Standard Time (EST) and Eastern Daylight Time (EDT) has other societal benefits, the one-hour shift would cause unnecessary disruptions to our records twice a year, so the Observatory operates on EST all year.
Why is there a horizontal curved mirror on the roof?
Long term observations of the clouds can be especially stressful on the neck. Although the mirror serves no official purpose, it allows visitors to look down at the clouds instead of up. Much more relaxing! In the early days of the Observatory they used a reflective instrument called a nephoscope to measure the movement and speed of the clouds. This instrument is displayed in our History Room, which is on the first floor of the Observatory tower.
Why is there an instrument that looks like a crystal ball on the roof?
The instrument with the solid glass sphere is not used to predict the weather, it is our Campbell-Stokes sunshine recorder. A treated paper card is placed in the frame below and at the focal length of the glass sphere so that the direct sunlight is focused into a bright, hot spot that makes a burn mark on the card when the sun is sufficiently bright. The length of the burn made on the card during the day (as the sun moves across the sky) gives us the duration of bright sunshine, from which a percent of possible can be derived, since the total possible minutes of sunshine from sunrise to sunset is already known.
Why are there plants growing on the roof of the other building on the summit?
These plants are a hardy type that can subsist in a “green roof” environment. A green roof uses plants to recycle precipitation and to minimize rooftop contribution to global warming. Recycling precipitation reduces contaminated runoff into groundwater supplies. In a rooftop environment without plants the ultraviolet light from the sun is converted to infrared (heat) and serves to warm the atmosphere. Planting the rooftop simulates the natural environment that was in place before the building was constructed. The plants remove carbon dioxide from the atmosphere and change the color from black to green thereby reducing energy absorption.
Why is there a tall metal tower on the summit of Great Blue Hill?
The 240-foot tower is the transmission tower for the WGBH-FM radio station. Multiple microwave dishes on the tower are used for other purposes.
Why do you fly so many kites?
There is a long history of using kites in meteorology. In the early days of meteorology, before airplanes and satellites, kites were frequently used to send weather observation equipment aloft. Measurements of temperature, humidity, and altitude were taken. Sometimes wind speed and wind direction were measured as well. At the Observatory, between 1890 and 1910, kites were sent as much as three miles above the surface to gather data. After completing the observation the kites were reeled back in so that the data could be recovered. The use of kites was eventually supplanted in the 1930s by the use of weather balloons with equipment that transmitted weather information to the ground by radio signals, a system still in use today at about 100 sites in the United States and many more across the world (though no longer at Blue Hill).


What are the instruments that can be seen outdoors in the fenced area near the Observatory?
The outdoor instrument enclosure includes the large, white Hazen temperature shelter, which we continue to use and was the standard way of measuring temperature during the 20th century, the precipitation gauges, a weighing rain gauge, the snow boards, and the ombroscope. You’ll have to visit to find out what the ombroscope does! In addition, the rainfall, temperature and dew point sensors for the automated ASOS observing system, which is operated by the NWS, are also in the enclosure.
Why is there an instrument that looks like a 'crystal ball' on the tower roof and in the History Room?
The instrument with the solid glass sphere is not used to predict the weather, it is our Campbell-Stokes sunshine recorder. A treated paper card is placed in the frame below and at the focal length of the glass sphere so that the direct sunlight is focused into a bright, hot spot that makes a burn mark on the card when the sun is sufficiently bright. In effect, it works like a magnifying glass. The card is marked in hours, so the length of the burn made on the card during the day (as the sun moves across the sky) gives us the duration of bright sunshine, from which a percent of possible can be derived, since the total possible minutes of sunshine from sunrise to sunset is already known. The similar sunshine recorder in the History Room was in daily use on the roof from 1898 until 1993, when it was replaced by the current recorder.
Why doesn't the sunshine recorder card burn up completely?
As anyone who has tried to start a campfire knows, starting a fire is harder than it looks. The focus of sunlight is so precise that it burns away any flammable material only over a narrow path (a fraction of an inch) as the earth spins and the spot moves thus preventing the card from burning up. Also, the card is treated to start burning at a specific intensity of sunlight and is designed not to burn completely. The fact that the direct sunshine is so much stronger in summer than in winter translates to burn traces that are much wider in summer than in winter and much wider in the middle of the day than near sunrise or sunset.
What happens to the recording sun card in the sunshine recorder when it rains?
Essentially, nothing. The heavy paper will get wet, but it has a coating to prevent it from getting too soggy. The winds on the tower and the sunshine when it returns, quickly act to dry the card. The recording card can remain in the sunshine recorder for several days without damage. What is more important is to change the card at proper times when the sun is shining to prevent over burn of yesterday’s data with today’s.
How do you measure snowfall?
Measuring snowfall is a tricky business. Snow blows around, makes drifts, compresses, sublimates (evaporates directly to water vapor), and melts. To measure snowfall we use snowboards (not the kind you ski on!). These are flat boards located in the gated instrument enclosure next to the Observatory building. And, yes, we do measure snowfall with a ruler. The measuring sticks we use are in 1/10th inch increments. Snowfall measurements are taken periodically during a storm and at the conclusion of the storm. Official snowfall amounts are reported based readings at six-hour intervals.
How do you have so many anemometers?
One of the key aspects of Blue Hill Observatory is that we maintain homogeneous data. By having multiple instruments we are able to ensure data are never lost and that all the instruments are working correctly. Also, different aspects of the wind, such as wind speed and peak gusts are measured with different equipment. Some of the instruments are official, some are back-up, and others are used for educational purposes. We sometimes receive donations of equipment from vendors who realize that the top of Great Blue Hill is an excellent location to demonstrate the capabilities of their equipment.
This equipment is part of the ASOS system operated by the National Weather Service. It measures wind speed and wind direction ultrasonically based on small changes in pressure between the arms of the sensor. The spikes on the arms keep birds off the equipment.
How often is the mercury barometer calibrated?
The mercury barometer has been in daily use since the 19th century, but it contains no electronics or moving parts. Although it has been evaluated several times during its history, its need for calibration is minimal. We are constantly checking the readings from the mercury barometer against other pressure instruments to make certain that the device continues to read accurately.


What educational programs do you offer?
We have a variety of programs for all ages. You can see most of them on our website on our Programs Page . Detailed descriptions can be custom written for your group.
How do I book a program or schedule a visit?
Please contact Program Director Don McCasland. You can phone him at 617-696-0562 or e-mail
My school/organization is on a tight budget. Do you offer free programs, or scholarships for programs?
Occasionally there are free Open Houses and afternoon programs (announced on Facebook), but all other programs have a fee. The current budget at Blue Hill Observatory & Science Center does not make it possible to offer free programs unless it is a girls’ group participating in the Women in Natural Science (WINS) program. In the future, we hope to get financial support from sponsors and other sources to make it possible to offer free programs to a variety of groups. We can offer discounts or barter to make it possible for you or your group to visit.
How many participants can there be in a program?
“Weather Watching at Great Blue Hill” can host up to 60 in one session though we suggest 40 or fewer. Group Program pricing is based on 20 people per session and is adjusted based on each specific group. We suggest no more than 16 for a simple “Observatory Exploration” program. We can do multiple programs simultaneously so we can host up to 180 people in one day. To work out the best plan and schedule for your school or group (even just a family) please contact Program Director Don McCasland at 617-696-0562 or e-mail-
Are minimum numbers of participants required to book a program?
Any number, including just one person, can book an educational program. The base fee covers the initial cost of the program. The per person admission helps cover expenses such as supplies, cleaning and other incidentals. The more participants, the lower the per-person price becomes. For small groups of 1 to 7 we can often modify a program to make the per-person price a little lower while still serving your needs.
Other than 'Kite Making', which programs do you offer at schools and other sites?
All of our educational programs are available at the Observatory or as Outreach Programs. For off-site programs we have modified them to be done using computer presentations and other visual aids. The pricing starts at $120.00 for up to two hours and varies based on the number of students, materials used and total time required. For specific pricing and scheduling please contact Program Director Don McCasland by phone at 617-696-0562 or by  e-mail at
During the 'Kite Making' program, what kind of kite will the students be making?
For most groups we suggest the Tyvek Sled kite. It’s easy to make and fun to fly. It is $5 per kite kit and is appropriate for all ages. Alternately, if we have one group of about 15/5 (there is flexibility such as 18/6 or 12/4) that wants to do a different kite we can do that. One group can do one kite and the other a different kite. It really depends on a combination of: your budget, group dynamics including age and interest, topics to be covered and time you have available.
For the 'Kite Making' program, is there a limit to the number of students?
Based on the space at your site, we can do up to 80 people in one session. There is a maximum of 24 in one session if the program is held at Blue Hill Observatory. For larger groups we can split the participants up into a kite making group and a weather Observatory group and then switch activities after a short break. Let’s say you have 30 students and 10 adults. 15/5 or so, depending on ages and family or class dynamics, would make kites while the other 15/5 do the weather program. There would be a short break for lunch and then the groups switch activities.