Astro-Event of the Week; 02.06.09: An Antares Occultation.

About 10PM EDT Looking East..(Credit: Stellarium).

An occultation of a bright star is well placed for observers in the Americas this weekend. The waning gibbous Moon will occult (i.e. pass in front of) the bright star Antares, also known as Alpha Scorpii. The action begins around 10:00 PM EDT and the Moon will cover up Antares for up to an hour and a half, depending on your latitude. Although the Moon will only be 16 hours away from Full, Antares at about magnitude +1 will be an easy naked eye target, and the skies will be completely dark along East Coast longitudes. The farther west you go, the lower (and in a brighter sky) the pair will be. A cycle of several Antares occultations are happening this year, as it currently lies along the Moon’s path. Observing and recording these events are always fun and beneficial; much of the lunar profile has been mapped this way. But an Antares occultation is special for another reason; a chance to spot its faint companion as it winks in and out! Antares gets its name from the Greek Αντάρης, meaning “rival of Mars,” due to its ruddy Mars-like appearance. I like to think of Antares as the “anti-Mars.” A red giant star an estimated 700 times the diameter of our Sun and about 600 light years distant, it is a good candidate for a galactic supernova one day (Romulans, beware!)…Another cool bit of Antares related scifi trivia; some treatments of the Superman tale place the doomed planet Krypton in orbit of this red giant star! You think Supes’ would mention this impending (for us!) supernova to scientists once in a while… It also has a hot blue companion, at a separation of about 3 arc seconds and a magnitude of +5.5. This companion would not be hard to spot, were it not in Antares glare. Astronomer Professor Burg of Vienna first sighted the elusive companion of Antares during an occultation similar to Saturday’s. The white dwarf companion of Sirius (Sirius B) is one of the few challenging double stars that is tougher. This week’s occultation is a good chance to test the resolution of that new telescope (and the quality of the local seeing!) and replicate this historical feat!

The Astro-term of the week is the Purkinje Effect. Does Antares B look a tad…greenish to you? Observations have described this as one of the very few stars that exhibit a shade of green over the years… this is most likely due to the Purkinje optical effect. In low light conditions, our eyes tend to switch from color sensitive cones to low light rods, kind of like fast and slow speed film (for those of us that remember film!) This is why things can look very black and white under low light conditions…but another consequence of this optical illusion is that some objects and stars can look greenish when contrasted with their red counterparts! The effect can be elusive, and not all folks see the same color contrasts when it comes to double stars. As Antares winks in and out watch for this effect… what differences do you see on film and video?