The Summer Triangle

Go outside about half an hour after sunset. One by one, the brightest stars in the sky will start popping out. If you look directly overhead, the first three stars to appear form the asterism known as the Summer Triangle. Even though it's almost autumn, the Summer Triangle is still high overhead at nightfall.

Vega, the star farthest to the west, is the brightest among the three. Altair, towards the south, is the second brightest. Deneb, the one farthest north, is the faintest.

Unlike other asterisms that usually belong to a single constellation, the three stars of the Summer Triangle belong to three different constellations. Vega is the brightest star in the constellation Lyra. Altair is in the constellation Aquila. And Deneb belongs to the constellation Cygnus.

References:

Skywatchers Guide: Summer Triangle helps orientation, observation

Arc to Arcturus

Find the Big Dipper and follow the arc of the handle to the brightest star you see, Arcturus. At this time of the year, it's high in the west. Athough Arcturus is only the 4th brightest star, it's the brightest one in the summer sky at magnitude 0.

The name Arcturus is Greek for bear guard. It watches over Ursa Major and Ursa Minor.

Arcturus belongs to the constellation Boötes (pronounced boh-oh-teez). The brightest star in a constellation is called alpha, and since Arcturus is the brightest star in Boötes, it is also known as Alpha Boötis.

References:

Arc to Arcturus
The 10 Brightest Stars
Arcturus

Finding North

I am constant as the northern star,
Of whose true-fix'd and resting quality
There is no fellow in the firmament.
- Julius Caesar (III, i, 60 – 62)

The stars at the front bowl of the Big Dipper, Merak and Dubhe, are called pointer stars. They point to Polaris, the North Star. Draw an imaginary line from Merak to Dubhe. Extend it five times the distance, and you'll end up at Polaris.


Contrary to Shakespeare, the North Star is neither constant nor fixed. Some facts about Polaris:

• It resides in the constellation Ursa Minor.
• It is the tip of the handle of the Little Dipper.
• At magnitude 2, it is only the 48th brightest star in the night sky.
• It is a variable star, its brightness varying over 4 days.
• It is a binary star or double star. The second star is a faint magnitude 9.
• It wasn't always the North Star. Thuban, in the constellation Draco, was the North Star around 3000 BC. In 3000 AD Gamma Cephei in the constellation Cepheus will become the North Star.
  

References:

Polaris
Wikipedia on the North Star
Wikipedia on Polaris
List of Brightest Stars
Constant as the North Star
Shakespeare Quote

The Little King

If you attempted to see the lineup described in the previous post, you saw the star Regulus between Saturn and Mars. What made this lineup possible is that Regulus lies near the ecliptic, the path followed by the sun. The moon and the planets also closely follow this path.

Regulus is the brightest star in the constellation Leo. The brightest star in a constellation is usually designated alpha. Hence, Regulus is also known as Alpha Leonis. In ancient times, Regulus was known as Cor Leonis, which means "heart of the Lion." The more modern name Regulus was given by Copernicus. It is Latin for "little king."

Through a telescope, Regulus appears as two stars. Though difficult, it is possible to see both stars through binoculars. The dimmer of the two is actually a double star itself. You can see all three stars through a large telescope.

One unusual thing about Regulus is that it spins very rapidly. As a result, it is 32% wider at the equator than at the poles. Astronomers think that a previously unknown star is causing the rapid spinning. You can read more about Regulus's secret companion here.

References:
Wikipedia on Regulus
S&T Regulus's Secret Companion