May's Featured Variable: V Star Finder Chart for V Hydrae Hydrae in Hydra the Sea Serpent I bet you have seen a star twinkling —the air It is easy to estimate the brightness surrounding Earth makes it look like the star ("magnitude") of a star, but first note: is sparkling! Even if we went to outer space, • in finder charts like below, brighter stars we could see many stars change brightness. are indicated by larger dots “Variable stars" continuously dim, brighten, • the brighter the star, the lower the magnitude number and dim. Some complete the pattern in under a second, while others take years. • magnitudes are written to the nearest tenth—but without a decimal point, to enable anyone, anywhere, to One variable star that YOU can see this which could be confused as a star. So, participate in scientific discovery month is V Hydrae in the constellation Hydra 45= magnitude 4.5 through variable star astronomy the Sea Serpent. Its deep cherry red color is • in this chart, magnitudes for comparison often bright enough to be seen about 5 stars—nearby stars to compare a given degrees south of the bright star Nu Hydrae, star's brightness to—are noted American Association of Variable Star Observers from a dark sky site, but it is more easily 49 Bay State Road, Cambridge, MA 02138, USA spotted in binoculars. Find two comparison stars close to your Telephone: +1 (617) 354-0484 given variable star's brightness—one www.aavso.org | [email protected] Why is this star amazingly red? The relatively brighter and one dimmer. Then observe—is cool red giant V Hydrae is a member of a rare the variable's brightness half-way between class of stars known as “Carbon Stars” the two comparisons'? A quarter? Really because of the relatively high concentration close? Apply that fraction to the difference in of carbon in the star’s atmosphere. This the two magnitudes and you estimated the excess of carbon is the reason for its deep star's brightness for that time! red color. This star comparison and finder chart for V Hydrae will help you estimate its brightness. As a semi-regular variable, it pulsates, with its brightness changing by a factor of 11 over The icon indicates the location of V a period of about 530 days. This period is Hydrae. superimposed on a longer period of 18 years where the brightness may drop even further, probably due to a surrounding disc of material obscuring the star’s light. Time Magnitude _______ ___________ _______ ___________ _______ ___________ AAVSO can help YOU About the AAVSO Connect with the AAVSO become a citizen astronomer! The American Association of Variable Star Who are AAVSO Members? Discover the benefits of membership and Observers (AAVSO) is an international join us! nonprofit organization of citizen and A citizen scientist—contributes to science professional astronomers interested in stars by acquiring data on variable objects and https://www.aavso.org/join-aavso#benefits that change in brightness—variable stars. submitting them to our databases, or other activities, such as data mining. Benefits include being able to participate in From its earliest days in 1911, AAVSO An educator or mentor—teaches our mentor program: beginners are paired members have included some of the most observing skills to fellow AAVSO observers, with an experienced observer for guidance prolific astronomers of the 20th & 21st through instructing AAVSO CHOICE courses and techniques: centuries. or being a mentor. https://www.aavso.org/mentor-program AAVSO Databases A student—is learning how to find a star, * * * * * set up a telescope, observe, submit data, or AAVSO International Database (AID): The is increasing their astronomy knowledge AAVSO Tools for Beginner Observers: largest and most comprehensive digital variable star database in the world, with over A professional astronomer— uses AAVSO Beginner Tutorials: aimed at those with 43 million variable star observations—a free data and services to advance their research absolutely no experience, these introduce resource for the entire scientific community An AAVSO Ambassador—a student or variable star science basics and then provide Variable Star Index (VSX): a collection of up- young professional representing AAVSO "challenges" for you to apply the concepts: to-the-minute data on over 200,000,000 through astronomy education and activities https://www.aavso.org/tutorials specific variable stars Interested in becoming an ambassador? • www.aavso.org/ambassador-program AAVSO Online Forum: talk to peers for Spectroscopy Database: spectroscopic • Email [email protected] advice: https://www.aavso.org/forum observations of stars * * * * * Solar Database: Sudden Ionospheric Observing Manuals: each one is dedicated Disturbance (SID) Database, and data relating You, your friends, and colleagues are also to a type of observing, including visual, CCD, to sunspot observations invited to join us for: DSLR, Spectroscopy, Solar, and more: https://www.aavso.org/observing-manuals Exoplanet Database: long-term follow-up AAVSO's free-to-all 2021 Webinar Series! information on planets orbiting other stars Come to one or all! Most Saturdays of the year. CHOICE Courses: peer-taught informal See the schedule and sign up: online observing courses: https://www.aavso.org/2021-webinars https://www.aavso.org/choice-astronomy Community Explore Education Let’s connect and explore.