A Lesson on Luni-solar Calendars for Losar

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[A Tibetan mandala, representing the orbits of the moon, sun, and planets]

February 27, 2017 marks Losar, the beginning of the Year 2144 on the Tibetan Calendar, a year of the Fire Bird. You might be saying, hey, wasn’t the Chinese New Year last month, and you would be correct. The Chinese New Year indeed fell on January 28 this year. Both the Han Chinese and Tibetans traditionally follow what we call luni-solar calendars, but despite their geographical proximity, these two cultures have very distinct rules for calculating their calendars.

Unlike our solar calendar of 365.25 days (called solar because it is based on the orbit of the earth around the sun), luni-solar calendars use the 29.5 day cycle of the moon’s phases to define 12 lunar months (normally 6 each of 29 and 30 day lengths) in their year. This means that a luni-solar year is too short, by about 11 days, and in response the holidays will drift earlier and earlier each year. To prevent this, every few years, an extra lunar month (called an intercalary month) is added, and the holidays move back to their original starting point relative to the seasons. You might have noticed that the Jewish holidays can drift somewhat relative to our solar calendar, but you never celebrate Hanukkah in July, for example. This is because the traditional Jewish calendar is also a luni-solar one. In contrast, the Islamic calendar is strictly lunar, so Islamic holidays (such as Ramadan) continually shift earlier and earlier relative to the solar year, occurring in different seasons as the decades pass.

But if both the Chinese and Tibetan calendars are luni-solar, why don’t their New Years occur on the same day relative to each other? This is because they have different calendars with very different rules. For example, the Chinese calendar adds an intercalary month about every 3 years. The lunar month begins at the astronomical New Moon, and there are specific rules for which months have 29 or 30 days based on the exact time of the New Moon relative to a specific longitude line (120 East). Chinese New Year falls on the day after the second New Moon after the Winter solstice (so it is often in February but sometimes in January, like this year). In contrast, in Tibetan Buddhism the phases of the moon are calculated by different rules, and the Full Moon must fall on the 15th day of any month, with the New Moon on the 30th day. So the Tibetan calendar uses skip days (tsi chad-pa) and doubled days (tsi lhag-pa) to accomplish this. Therefore a particular month might have two 19ths and no 23rd (roll that around in your head for a while!). Intercalary months are added about every thirty lunar months, and which months have 29 versus 30 day months are decided by the phase of moon at sunrise. New Year (Losar) is traditionally the first day of the first lunar month of the year. It does not always fall on Chinese New Year because the rules for calculating intercalary months, phases, and defining which months have 29 and 30 days differ. It will not surprise you to learn that the rules for calculating the Tibetan calendar are complex, and passed down from master to student.

So Tashi Losar to all my Tibetan friends, and if you want to learn more about Tibetan cultural astronomy, peruse the following page.

-Kris Larsen

 

My Favorite Martian… Research Project!

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[Dr. Jennifer Piatek presenting her research on Mars at a recent conference]

Did you know that students at CCSU can do real science research projects with faculty mentors? These projects can lead to presentations at professional conferences and/or publications in professional journals, making YOUR resume shine! For example, students working with Dr. Jennifer Piatek can study the surface of Mars and students working with Dr. Kristine Larsen can focus on variable stars, stars that change brightness over time. Visit the Geological Sciences Department on the 5th floor of Nicolaus Copernicus Hall and be sure to look over all the research posters hanging in the hallways. See yourself at CCSU doing real scientific research!

Astronomy is “above the fold” today!

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Astronomy is front and center today, appearing “above the fold” on the front page of The New York Times. Unless you’ve been spacing out, already know about the discovery of seven earth-sized planets orbiting the relatively nearby (39 light years) star TRAPPIST-1. What you might not know is what it all means. TRAPPIST-1 is only the second known star to host a stellar system of seven planets, and also has (by far) the largest number of small, rocky, earthlike planets. While the inner three planets (dubbed b, c, and d) are probably too hot for liquid water to be prevalent, and the outermost (called h) is too cold, the other three (e, f, g) are, to steal from Goldilocks, “Just Right.” But before you start packing for a visit, you should know that there is a big difference between this star system and our own, namely the star itself! TRAPPIST-1 is barely a star, what we call an “ultra cool red dwarf.” It is barely massive enough to “shine,” to create energy via nuclear fusion of hydrogen into helium (the actual definition of a true star). At only 8% the mass of our sun, this is surely no “superstar!” In order for these planets to be in the Goldilocks zone (also called the habitable zone), they are so close to their star that they are almost certainly tidally locked. This means that they always keep one side facing the star (in eternal daylight) while the other side is always facing away (in eternal night – sounds like a vampire paradise, doesn’t it?). This means that IF the planets have atmospheres, their climates are pretty darned complicated, to say the least. But regardless of whether or not TRAPPIST-1’s planets really could support life as we know it, they have taught us an extremely important lesson, one that Copernicus himself tried to instill in us – we are NOT the center of the universe, and we should never make the mistake of thinking that our “normal” is the same as every other star system’s “normal.” Variety really is the spice of life, at least as far as the universe is concerned.

Welcome to CCSUniverse

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[Our observatory dome all decked out for Halloween]

Welcome to the blog of the CCSUniverse, Astronomy at Central Connecticut State University! Our facilities feature the Copernican Observatory and Planetarium, as well as a host of portable telescopes that are all available for use by students and the general public without cost. Housed in the Department of Geological Sciences in Nicolaus Copernicus Hall, we offer minors in Astronomy and Astrobiology, as well a wide variety of courses. Follow us on Twitter @CCSU_Astronomy .