Navigating the Northern hemisphere

The Big Dipper can be used reliably to find your way around the sky and around Earth as well. Here’s how:

step 1) Locate the Big Dipper

The Big Dipper is very iconic and with its bright stars it’s usually one of the first things to jump out at you. Currently look for the Big Dipper very low in the northern sky (slightly east of due north) just after sunset. Depending on the time of year at sunset, the Big Dipper ranges from in the north-east from February to March, high in the north from April to May, in the north-west from June to October, and very low on the northern horizon November to January.

step 2) Find the North Star (Polaris) with the Big Dipper

One of the reasons the Big Dipper is so iconic is because it has been used for centuries to find the North Star. The two stars that make the end of the vessel of the Big Dipper are called “the pointer stars” because they point at the North Star. Make an imaginary line with these stars and trace it until you run into another star of similar brightness to the pointers, this is the North Star. (it’s a common misconception that the North Star is a particularly bright star; it’s really of similar brightness to the stars in the Big Dipper).

step 3) Find north with the North Star

Now that you found the North Star all you have to do is drop a line directly down to the horizon from that star and that’s due north!

Step 4) find your latitude with the North Star

The North Star can also tell you latitude; all you have to do is measure what angle the North Star is above the northern horizon and that’s your latitude. There’s a very ‘handy’ way of doing this with the pointer stars (the stars at the end of the vessel of the big dipper). Hold your hand out at a full arms length and measure how many fingers fit between the pointer stars (usually three fingers). The pointer stars are almost exactly 5 degrees apart so now all you have to do is count how many fingers fit between the horizon and the North Star and you have a rough estimate of how far north you are on the planet.

For example Baseline Road in south Boulder is called “baseline” because it is surveyed to be on the 40th parallel. If three fingers fit between the pointer stars, you would find standing on the sidewalk of Baseline Road eight sets of three (or 24 fingers) fit between the horizon and the North Star proving Baseline Road is exactly 40° north.

Baseline Rd extending across Colorado as seen from Sunrise Amphitheater

Tip: for the longitude measurement to work you have to start on the true horizon. Imagine you’re on a boat in the middle of the ocean, where the water meets the sky is your true horizon. Do not use trees/buildings/mountains as the start of the horizon as measuring up any higher than the true horizon will make your measurement inaccurate.

Venus

Watching the sky just after sunset you may be noticing the brightest star that appears over the western horizon. This “star” is actually a planet, Venus.

cloud patterns on Venus

Venus is the third brightest naturally occurring object in our sky (after the Sun and Moon) due to having a thick atmosphere with clouds that reflect sunlight really well. Venus is the closest planet to the Earth and about the same size as Earth both of which also attribute to its brightness.

Venus's movement in the sky over months

The key to understanding Venus’s movement in our sky is to remember it’s an interior planet which means it travels around closer to the Sun in an orbit interior to ours. It takes Venus a little over 7 months to travel around the Sun where it takes Earth 12 months. This means every year Venus will pass us on the inside lane at least once. Right now Venus is catching up and will pass us on the inside lane on January 9th 2022. This is called ‘inferior solar conjunction’ and means the Sun, Venus, and Earth will be in alignment. We won’t be able to see it pass us as it will be too close to the Sun to observe. Here in the Front Range, we will stop being able to see Venus in our evening sky in late December due to the mountains covering anything low on the western horizon.

We can’t watch Venus pass us, but right now we can watch it move in for the pass. If you watch the sunset every week or so until December you will see Venus getting closer and closer to the horizon. A few days after inferior solar conjunction (January 9th 2022) we will start seeing Venus on the other side of the Sun in our sky just before sunrise. Watching the Sun rise starting in February you will see Venus climb higher and higher in the morning sky. Venus never travels further than 47 degrees from the Sun. Because of this we only notice Venus at sunset or sunrise when the Sun is blocked by the horizon letting Venus shine in the sky. One small exception to this is during a solar eclipse when the Sun is blocked by the Moon. Some may have noticed Venus next to the Sun during the 2017 solar eclipse.

Phases of Venus

Looking at Venus with a decent pair of binoculars you will see that it currently appears as a crescent. This is because just like the Moon, Venus has phases. Because Venus is currently coming toward us, we can see a portion of Venus that is illuminated by the Sun and a portion that is in darkness (night) facing away from the Sun. The illuminated portion will continue to shrink until Venus is in inferior solar conjunction when we won’t see Venus just like we don’t see the Moon at New Moon. Then in February as we watch Venus rise before the Sun we will also see the illuminated crescent grow larger, if we check in weekly with binoculars.

If you want to see Venus up close in a big telescope Book an AstroTour in November to be sure to catch it before it moves to the morning sky not to be seen on a tour again until 2022.

Saturn & Jupiter

Saturn reached 'opposition' (closest it'll be to Earth all year) on Aug 2nd and Jupiter reached opposition Aug 19th meaning now's the best time to see both of them!

Saturn is currently appearing in the southeast next to Jupiter (the brightest 'star' in the southeastern sky after sunset) in our evening sky. Saturn is much dimmer than Jupiter but it is much brighter than the stars that surround it. Saturn makes almost a straight line in the sky with Jupiter currently at sunset.

Location of Jupiter and Saturn

Saturn is a true treat in binoculars or a telescope. When you first see it you might see an oval resembling a batman symbol but once you focus your eyes on it you should see Saturn's rings resolve. Saturn never fails to get an “oh wow!” from anyone looking at it up close, the large planet suspended perfectly in the rings is a magical sight to observe with your own eyes. If you really want to test your eyes and equipment you might see ‘the Cassini Division’ which appears as a dark region that separates the bright ring into 2 rings. The rings are made up of countless water ice particles ranging in size from the smallest speck to the size of a house.

Saturn, like the Earth, has solstices and equinoxes. Saturn takes 30 years to go around the Sun meaning 30 Earth years = 1 Saturn year. We see Saturn's solstices by seeing the rings tip towards us and appear to open up and we see Saturn's equinoxes by observing the rings edge on, where it’s difficult to notice the rings at all. Saturn is currently going into equinox, meaning 2021 will be the best time to view the rings till 2028 when they start to open up again

The brightest ‘star’ appearing in the southeast is actually the planet Jupiter. Jupiter is the largest planet in our solar system at 11.6 times the size of Earth in diameter (86,881 miles), making it 1,322 times the size of Earth in volume. You could fit over a thousand Earths inside Jupiter. Being so massive has made Jupiter a solar system within our solar system, as its extreme gravitational pull captures lots of objects as moons of Jupiter.

Jupiter and 4 moons as seen in a pair of binoculars.

If you look at Jupiter with a decent pair of binoculars you will be able to see 4 of Jupiter's moons: Io, Europa, Ganymede, and Callisto. These are called the Galilean Moons as they were first observed by Galileo in his small telescope. They are very easy to make out even in small telescopes/binoculars. Telling which one is which takes several observations over a longer period of time as they are circling Jupiter and you can only see this movement edge on from Earth. To determine a moon’s true distance from Jupiter you must watch the moons to see when they stop getting further from Jupiter, turn around and get closer.

All of the Galilean Moons are interesting places and studied extensively. Io (the closest) is the most volcanic body in our solar system. Europa is the smoothest body in our solar system; it’s believed to have liquid water and therefore possibly life beneath it’s Ice surface. Ganymede is bigger than the planet Mercury, and Callisto (the furthest out) is the most cratered body in our solar system. With a good pair of binoculars you can also see red stripes contrasted with white stripes; this is Jupiter’s atmosphere. The change in coloration is caused by different compounds in the atmosphere that change color when exposed to the light of the Sun.

With a really good set of binoculars or a decent telescope you can see the red spot which is an acid hurricane more than twice the size of Earth that has been observed since at least 350 years ago. A day on Jupiter lasts about 10 hrs, so over the course of a long winter night you can watch Jupiter do a full rotation by watching the great red spot do a lap around the planet.

If you want an up close view of these planets and more please join me on one of my astronomy programs.