Stars of Lacerta

There are two lizards in the night sky. Were classical civilizations enthralled by small reptiles? Not at all, for both Lacerta (the Lizard) and Chamaeleon are considered “modern” constellations. They're only comparatively modern, dating from around the 17th century. Petrus Plancius had introduced the Chamaeleon on a sky globe, but Lacerta was the creation of the great Polish astronomer Johannes Hevelius (1611-1687).

The lizard triumphs
Hevelius's sky atlas Firmamentum Sobiescianum was published posthumously in 1690. It included a number of constellations he invented to fill the gaps between existing constellations. Seven of these were adopted generally, and eventually made it into the modern official 88 constellations.

There seemed to be a tempting group of dim stars in a space surrounded by Andromeda, Cassiopeia, Cepheus, Cygnus and Pegasus. Hevelius made Lacerta the lizard out of the stars because he couldn't think of anything else to fit the space. He also gave it the alternative name Stellio (a Mediterranean lizard), but that didn't catch on.

Although Hevelius thought “lizard”, there was some competition for that area of sky. French astronomer Augustin Royer published a star map that included a tribute to his patron King Louis XIV in the form of a new constellation Sceptrum et Manus Iustitiae (The Sceptre and the Hand of Justice). It represented two symbols of royal power.

Later, German astronomer and celestial cartographer Johann Bode (1747-1826) claimed some of the stars for the creation of Gloria Frederica in honor of his monarch Frederick the Great of Prussia.

The royal constellations faded away, as did the monarchies they represented, but the lizard remains.

Stars and planets
The five main stars of Lacerta form a W shape, which is sometimes called “Little Cassiopeia”. However it's a very dim W compared to that of bright Cassiopeia.

Lacerta's brightest star Alpha Lacertae is a blue star twice the size of the Sun and many times brighter. It seems dim to us because it's 100 light years away. The second brightest star, Beta Lacertae, is noticeably dimmer than Alpha Lac, even though it's a yellow giant more luminous than Alpha Lac. However it's 170 light years away from us.

If you look at Alpha Lac through a telescope, it seems to have a very dim companion. This is a line-of-sight effect. The second star isn't part of a binary system with Alpha Lac. It's over 2500 light years away from Alpha Lac.

Yet there are many multiple-star systems in Lacerta, most spectacularly the quintuple system Roe 47 and the sextuple 8 Lacertae system.

One binary star ADS 16402 consists of two fairly widely separated Sun-like stars. John Herschel discovered it in 1831, but it only became of special interest in 2006 when the HATNet Project discovered that ADS 16402B had an orbiting planet.

The HATNet Project designated the star HAT-P-1 and its planet HAT-P-1b. The planet is a hot Jupiter, a massive planet orbiting close to its star. HAT-P-1b zips around its star in 4.4 days.

Although there are many known hot Jupiters, this one was uniquely strange. It was bigger than Jupiter, but much less massive, giving it a density about the same as that of cork. More of these puffy planets have been discovered since then, but they're still a mystery.

The Lacertan star that commands the most attention is EV Lacertae. This is a star with a ferocious temper! Although it's a red dwarf, which should make it quite unobtrusive, it was certainly noticed on April 25, 2008 when NASA's Swift satellite detected a flare.

Our Sun occasionally gives off flares with millions of times more energy than atomic bombs. They are one component of space weather and effects on Earth are moderate. Fortunately, we're 16.5 light years from EV Lac, because the flaring that Swift detected was thousands of times more energetic than that from our Sun. EV Lac is a young star which hasn't had time to settle down like the 5-billion-year old Sun. It spins very rapidly, generating a strong magnetic field, which is probably what releases the flares.

Deep-sky objects
Like most other dim constellations, Lacerta has no Messier objects. Any deep-sky objects are telescopic objects, and they include a few star clusters. But there is one very exciting deep-sky object: BL Lacertae.

The name BL Lacertae is a star designation. When it was discovered in 1929, it seemed to be a dim variable star. Fast forward to 1968, and it was identified as a bright radio source, not something you'd expect of a star. It is, in fact, the nucleus of an elliptical galaxy called a blazar.

There are a number of galaxies whose nuclei are notable sources of high energy radiation, each powered by a supermassive black hole. Some of the matter falling towards the central black hole is accelerated outward in two energetic jets, pointing in opposite directions. The matter in these jets is traveling at nearly the speed of light. If one of the jets is pointing in our direction, it's extremely bright and called a blazar.

More of these objects have been discovered since 1968 and they're all grouped as BL Lacertae objects.