Leo ... and You
15th century. Genoan. Credit: Andolone dal Nero
From the British Library, under Creative Commons CC0 1.0 Universal Public Domain Dedication.
Our lead story is … galaxies! We usually don’t emphasize them because common knowledge tells us that to see all but Andromeda Galaxy a good size telescope is required; however, our primary source, Robert Burnham, claims that a good pair of binoculars on a dark night can acquire two or maybe a handful of Leo’s galaxies, namely M65, M66, M95, M96, and M105 [see the Leo Gallery]. As shown in the chart below, there are two knots of them, one under the hind quarters and another under the belly. [see projects]
Credit: Torsten Bronger. Creative Commons Attribution-Share Alike 3.0 Unported license.
Many cultures have regarded the constellation as a lion. Leo’s head has been found minted on coins as early as 500 BCE. Observations were recorded on clay tablets in 2100 BCE.The forward (western) portion of the Lion has a formation of stars that suggest a reversed question mark … or a lion’s mane. At the base of this asterism is Leo’s heart – the bright star Regulus which means “Little King.”
Another twinkler in Leo’s mane is the fine double star Gamma Leonis also known as Algieba. This is a long period binary system which takes several centuries to complete one do-si-do. Both stars are a golden yellow, nearly twins. The orbit is very eccentric and the apparent separation of the two will widen to five seconds of arc by the year 2100. Even so, a telescope will be needed to detect the pair. [see projects]
Gamma has another significance in that it lies close to the radiant of the annual Leonid meteor shower. Each November our Earth passes through a region of debris left by Comet Tempel-Tuttle and we get a shower of bright, fast, short-lived shooters. They seem to fan out from a location near Gamma. If you ever see one you’ll never forget it and you’ll look for more. It seems that the Earth hits a heavy patch every 33 years or so and the meteor count gets exciting. Aunt Claire and I saw 632 of them in the wee hours in 2001. Some were bright enough to shine through the popcorn clouds which came and went that night.
Last but not least, at the eastern end is the beta star Denebola, marking the lion’s tail. It is dimmer than Regulus, but it provides a reference point to help find galaxies M65 and M66, in the Gallery.
… and You
1. We called the Lion’s mane an asterism. This term refers to a recognizable pattern of stars that is only part of a constellation. Many think that the Big Dipper is a constellation, but it is in fact a large part of Ursa Major, the Great Bear. Here is a table of other well-known asterisms.
What does the rest of the Bear look like? Can you find it in your sky? Sketch it?
2. Why does Gamma Leo require a telescope? I have seen the separation of these two yellow stars in a 10-inch scope at 100x magnification. If we assume a separation of 4 seconds of arc to the unaided eye, the magnification widens that to 400 seconds or nearly 7 arc minutes. According to Fred Schaaf [Seeing the Deep Sky, Wiley,1992], this is wide enough for normal eyesight to detect separation. Binos don’t come with mags like that.
3. Size and brightness of Leo’s galaxies. What will magnification do? Have a look for them. These galaxies are over 30 million light years away. Their apparent sizes are in the range of twice the separation of Gamma Leonis, but they are much fainter in brightness. M65 and M66 may be your best chances to observe in binoculars, but conditions would have to be extremely good.
4. In our ever expanding universe, most objects are detected as moving away from us. The double star Gamma Leonis is one exception, said to be closing at 22.6 miles per second. First take a minute to think about covering 23 miles in one second. Next, we’ll figure whether that constitutes a threat to Earth. Gamma is 90 light years away. Light covers 186,000 miles in a second. Can you estimate the time it will take Gamma to reach us? Answer below, but don’t peek – do the math!
Primary Source: Burnham’s Celestial Handbook.
Progress from previous months' challenges. UB braved the cold on the eve of March 15th. Three short stays outside – well worth it. In 10x30 binoculars I surveyed from west to east. Saw the Trapezium, the four brightest stars among Orion's M42 nebulosity. The Auriga clusters revealed a very few individual stars, but stars in Gemini's M35 were all distinguishable. Sweeping from Gemini to Leo, you pass the Zodiac's Cancer and its very large and bright Beehive Cluster. Leo was still coming into view, so will try again at later date. –UB
Answer to #4 above. We’ll use round numbers. Say Gamma is coming at us at 25 miles per second and light covers 200,000 miles per second. Yes, that’s an affront to the great Einstein and his constant c. Gamma is coming at an 8000th part the speed of light. It needs to cover 90 light years, or 720,000 Gamma-speed years. Hmm. That’s less time than I expected … and it would have a huge impact on our climate, unless … unless … we shoot the Gamma gap. Ha!