Vega’s role in astronomy
Did you know there's a Vegan anniversary this month?
No, we're not celebrating veganism. Instead, we're recognizing a stellar anniversary of sorts — the 171st anniversary of the first star to be photographed.
The star Vega, in the constellation of Lyra — the Harp or Lyre — shines almost directly overhead on summer nights by about 10 p.m. ADT (10:30 p.m. NDT). As it only dips below the horizon for about seven hours as it swings across the night sky, Vega is visible, weather permitting, any night of the year.
Along with Deneb (in Cygnus — the Swan) and Altair (in Aquila — the Eagle), it forms the recognizable asterism of the Summer Triangle.
On the night of July 16-17, 1850, Vega became the first star, other than our sun, to be photographed.
It was also the first star, other than our sun, that was spectrographically imaged in 1872, and to have its light broken down to reveal its various elements. At magnitude +0.03, and located approximately 25 light-years (240 trillion kilometres) from Earth, Vega is thought to be about 450 million years old, and as such is a relative newcomer to the stellar household. It is the fifth brightest star in the whole sky, and the third brightest in the Northern hemisphere after Sirius (Canis Major) and Arcturus (Bootes).
Vega also holds another special honour: it was once our North Star. As the Earth spins on its axis, it wobbles slightly, so that the North Pole (extended out into space) transcribes a circle on the sky (referred to as "precession") of approximately 26,00 years duration.
This means that, over time, different stars along the arc of the circle become the North Star as viewed from Earth. Vega was the North Star about 14,000 years ago, and will, in approximately another 12,000 years, once again become the North Star. Though most people have difficulty finding our current North Star (Polaris in Ursa Minor — the Little Bear), future generations will have no difficulty identifying the North Star.
This week’s sky Rising shortly after 4 a.m. ADT (4:30 NDT), Mercury (magnitude -0.3, visible in Orion — the Giant) reaches its highest altitude (12 degrees) in the eastern sky on the morning of July 12, but will only appear about seven degrees above the horizon at dawn, and may, therefore, be difficult to spot.
Venus (magnitude -3.9, look for it in Leo — the Lion) becomes visible around 9:25 p.m. ADT (9:55 p.m. NDT) nine degrees above the western horizon as the sky darkens, before sinking towards the horizon and setting about 10:35 p.m. ADT (11:05 NDT). Venus sits a mere 0.5 degree above Mars in the evening sky on July 13.
Mars (magnitude +1.8, also seen in Leo) will be extremely difficult to see, as it is only 2 degrees above the horizon at dusk. Once you have located Venus, a good set of binoculars and an unobstructed view of the western horizon may allow you to spot dim Mars in the post-sunset twilight before it sets.
Saturn (magnitude +0.3, seen in Capricornus - the Sea Goat) becomes visible around 11:20 p.m. ADT (11:50 p.m. NDT) 10 degrees above the southeast horizon. It reaches a height of 25 degrees in the southern sky by about 2:50 a.m. ADT (3:20 a.m. NDT), before being lost in the morning twilight by about 4:50 a.m. ADT (5:20 a.m. NDT).
Jupiter (mag. -2.7, spot it in Aquarius — the Waterbearer) is visible seven degrees above the southeast horizon by about 11:45 p.m. ADT (12:15 a.m. NDT), reaching an altitude of 31 degrees above the southern horizon by about 4:05 a.m. ADT (4:35 a.m. NDT), before it too is lost in the dawn twilight.
Until next week, clear skies.
EVENTS
July 17 — First quarter moon
Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. He welcomes comments from readers at glennkroberts@gmail.com.