Visits to the
Large Millimeter Telescope Alfonso Serrano & HAWC

The LMT is located at an elevation of 4581 m (15030 ft). It is considered a high-altitude mountain, with extreme meteorological conditions and low oxygen content. The altitude imposes an additional physical stress on the body, which not all visitors will be able tolerate. Please read carefully these instructions before planning your visit.


The group of people more prone to experiencing problems related to high altitude are believed to be those who suffer or have suffered from cardiovascular or pulmonary conditions, children and youngsters under the age of 18 and pregnant women. This group of people is strongly advised to avoid visiting the site unless they have previously obtained medical clearance. People who have repeatedly experienced high-altitude sickness symptoms are also strongly advised to pass a medical examination before visiting the LMT site, to prevent putting their health at risk.  


The high-altitude of Tliltepetl imposes an oxygen concentration in the air of only 60% of that at sea level. A low oxygen concentration in the blood-flow, or hypoxia, can trigger different levels of sickness in different people, and can vary over time in an individual person. While most people visiting the LMT site will experience no discomfort, some might experience mild symptoms of “altitude sickness”, which include headaches, drowsiness, nausea, shortness of breath, reasoning impairment, dry coughing, vertigo. If these symptoms persist or intensify, please notify immediately the leader of your group. At the LMT site we have first-aid equipment, oxygen and qualified staff to assist in a medical emergency.

In order to avoid altitude sickness, please follow these recommendations:

  • Walk slowly around the LMT site and avoid any strenuous movements.
  • Eat lightly before ascending to the site, and stay well hydrated by drinking constantly small quantities of water during the visit.
  • Avoid drinking alcoholic beverages the night before.
  • Do not smoke before and during the visit in order to enhance the oxygen concentration in your blood. Smoking is forbidden inside the LMT building.

At the site the temperature might drop to 0º C (37º F) and the ultraviolet solar radiation is very high. You are advised to bring with you a heavy coat with hood, gloves and hiking boots. Use sun-block and sun-glasses at all times, even if it is cloudy. If you are allergic to dust, consider using a mask.

The LMT site is within the National Park Pico de Orizaba, a protected natural area. Altering the ecological equilibrium or damaging in any way the natural resources within the National Park is strictly forbidden and prosecuted by law.


  • Confirm the attendance with three days in advance
  • At the site all visitors should remain together, always accompanied by the LMT guide.
  • Having been informed of the possibility of experiencing altitude sickness during your visit to the site, please sign the attached disclaimer form and send it by FAX to marrieta@inaoep.mx when you confirm your attendance.


$200.00 Mexican Pesos

IMPORTANT : if your attendance is not confirmed, you'll not be allowed to access under any circumstance.


Malinalli Arrieta marrieta@inaoep.mx Tel: 01 (222) 2 66 31 00 ext. 3303