In mid-month August, we can take off the mosquito netting and re-acquaint ourselves with the Night Sky . Let’s look at what we have been missing in the Southwest … as we wait for the Perseid Meteor shower peaking around midnight on the night of August 12.
Saturn is low and to the West of Antares -the bright yellow star in Scorpius. It is the next bright object in the area, and through a small telescope you can show your friend that – “it’s not a Star – it’s a Planet! ” In a telescope, you can see some of Saturn’s rings, slivers appearing as tiny as your fingernail. When planets appear above the horizon in the summer time, their altitude is low because they are located opposite the Sun with respect to Earth. The Sun’s altitude reaches the highest declination (and altitude) during Summer Solstice.
There are two very different globular clusters to check out in this Scorpius.. First locate Antares, the bright yellowish star, and sweep down towards the direction of the bottom star of the 3 bright stars to the right. Don’t go too far – just enough to get Antares out of your field of view if you are using a low-powered eyepiece in a telescope. M4 is one of the nearest open clusters and appears fairly large and diffuse in the eyepiece.
Let’s compare Messier Globular M4 to Messier Globular Cluster M 80 – which always tickles me by the contrast .
Sweep up M80 half-way between Antares, and Beta Scorpius, the top one of the three vertical stars (Its common name is Graffias – it’s actually composed of two stars, a double star). You will spot a bright but much smaller condensed ball of stars – impossible to resolve any pinpoints of light (individual members) . It is a rich and condensed globular cluster and contains some interesting members:
“This dense stellar swarm contains several 100,000s of stars, held together by their mutual gravitational attraction. It is one of the densest globulars in our Milky Way Galaxy. As was found by astronomers from observations with the Hubble Space Telescope in 1999 in the visible and UV part of the electromagnetic spectrum, M80 contains a large number of so-called “Blue Stragglers” in its core, about twice as much as any other globular investigated with the HST. These stars are blue and bright stars which appear near the main-sequence of the Hertzsprung-Russell diagramm, and thus appear more massive and younger than the globular clusters age. The reason is very probably that these stars lost their cooler envelopes in close encounters with other stars. Their large number in M80 indicates an exceptionally high stellar collision rate in the core of this globular cluster.”- courtesy http://messier.seds.org/m/m080.html
At almost 5 times the distance into interstellar space, we see what appears to be a much smaller object. It is bright even at that distances due to the high density of stars contributing to the surface luminosity. We experience the size discrepancy in the (cosmic) distance .
Distance to M4 ~ 7,000 Light Years Distance to M80 ~ 32,0000 Light Years
The Perseid Meteor Shower:Public Star Night – Aug 13 at the Mill of Kintail – After 9pm
According to the FLO Sky Clock ,it will be clear. Come and join us at the Mill of Kintail ( link on google map ) after 9pm as we stay up and tuned to the North horizon for the Perseid meteor shower . The meteor shower will peak around midnight . Why do we see more, faster meteors after midnight?
It is because the Earth itself is travelling at about 30 km/sec (67,000 mph) as it revolves around the sun. On the evening side, or trailing edge of the Earth, meteoroids must catch up to the earth’s atmosphere to cause a meteor, and tend to be slow. On the morning side, or leading edge of the earth, meteoroids can collide head-on with the atmosphere and tend to be fast. see Meteor FAQs . For more information of the Perseids observed a couple of years ago, see: Millstone NightSky – The Perseids
You don’t need any special instruments for this event – as we pass through the orbital tracks of Comet Swift-Tuttle, we can observe tiny particles of debris hit our atmosphere. Most likely there will be telescopes out after 9pm to also show you some celestial treats in Scorpius, Sagittarius and the Summer Milky Way.
Image – courtesy Sky and Telescope Plan for the Persieds…