During the month of June 2016, three bright planets appear in our evening sky. As shown in this diagram Jupiter appears in the western sky, then scanning eastward the Moon, Mars, and then Saturn appear along the Ecliptic (path of the planets). The red giant star Antares is also bright, but don’t confuse it with the planets.
In June, astronomers don’t have a lot of time to observe at night because summer solstice occurs around June 21 making daylight linger well into the evening.
In fact, it doesn’t get sufficiently dark until the sun has set 18 degrees below our horizon…This twilight condition is called “astronomical twilight” and it does not happen until after 11pm ‘daylight savings time’ for our latitude of 45 degrees during the month of June.
Astronomical Twilight is defined to be the time at which the sun is set below the horizon by 18 degrees. This is when the sky above our horizon is truly dark. Point light sources such as stars and planets can be readily studied by astronomers before astronomical twilight – i.e before the sky glow from the sun is gone. But diffuse light sources such as galaxies, nebula, and globular clusters need to be observed under a totally dark sky, when the sun is more than 18 degrees below the horizon. – courtesy http://www.weather.gov/fsd/twilight Fortunately in June 2016, we have 3 planets gracing our evening sky, and they are certainly bright enough to observe even under moony and June-y conditions!
Jupiter – in the Constellation Leo the Lion
The first planet to observe this month is Jupiter. Even in binoculars you can see the 4 closest moons. A telescope can afford a view with more detail…
Night Sky Course participants wrote up this observing session in May:
“Last night stargazing at the Mill we had my daughter (Mary Anne) with us. She saw Jupiter for the first time through a telescope and this morning drew a picture of what she saw. I have attached a picture of the drawing for you. We did explain to her that what she saw in the telescope was upside down…so the moons are depicted as she saw them…”
This planetarium image above shows the view of the moons on the night that Mary Anne observed them. In the reflector telescope, the image of the planet and moons shows South up. But in a planetarium image, you see the planet and moons with North Up. Since the top of Jupiter in Mary Anne’s image is the South Pole of Jupiter, we see the moons in the telescope upside down – not like binoculars or the planaterium program. Notice also that Mary Anne saw a darker shade at the bottom of her image which in fact is Jupiter’s North pole! (see illustration below)
In a telescope, with sufficiently high magnification (eyepieces with lower focal length numbers like 10mm), you can easily see features such as the North and South Equatorial Belts, and possibly the Great Red Spot, and other cloud formations. However Jupiter’s rotation period is under 10 hours so you have to be quick in what you sketch, and you may not be seeing all the features as shown.
When astronomers use instruments that record longer wavelengths (infrared in this case), we really get to see light reflected from the planet Jupiter, and not reflected sunlight. What we see in this image is hotter gases below the upper cloud decks. Cold, high-altitude ammonia clouds look black (as they absorb energy) and the bright bands record infrared energy from deeper down that’s escaping between the clouds. The longer the wavelength we record, the deeper we see down into the atmosphere. See https://en.wikipedia.org/wiki/Atmosphere_of_Jupiter
Mars – Low in the East ( and getting smaller)
Mars reached opposition (straight line Sun-Earth-Moon) in May. As it moves away from opposition and away from Earth in its orbit, the apparent size decreases.
Mars is a very difficult planet to observe when it comes to identifying features. However with sufficient patience (and imagination) and higher magnification through a telescope, we might be able to see deserts and dusky markings such as the bright Tharsis and the dusky Syrtus Major. This guide is courtesy SkyNews magazine now published by the Royal Astronomical Society of Canada (RASC). www.rasc.ca
Saturn – Low in the East near Mars
Saturn reached opposition on June 3 when it rose above the horizon at sunset (late!) and shone its brightest for 2016. Since Saturn and Mars appear so close together, its no surprise that Saturn comes to opposition shortly after Mars. The ringed planet is found near the constellation Scorpio and makes a trio with Antares (brightest star in Scorpio) .
The Stellarium illustration below shows the planets on June 3:
Unlike Mars, Saturn has very distinct features when looking through a telescope. Notice the rings which you can only see with sufficient magnification – (i.e viewing with a telescope, not binoculars). For this apparition of the planet (June 2016), the rings are now titled 26 degrees to our line of sight – so they are not being foreshortened unto the globe of the planet. Also, since the rings reflect twice as much sunlight as the planet, (more surface area), we get a nice bright image. So, as the June 2016 Sky and Telescope reporters suggest – it is a good time to see how much detail we can see in the rings…
- Cassini Division – can we trace it all the way round ?
- The fuzzy C ring close to the globe of the planet – can we see it against the dark background of space ?
- Notice the difference in brightness A, B, C rings
You will need to capture the light from Saturn with a medium sized telescope, say 6-8″ aperture to observe fine detail.
Light from the Planets: Unlike stars that are several light-years away, planets orbit in the plane of the ecliptic at distances much closer to Earth. However there is still a time delay for the light to reach us, due to the time it takes for light to travel from the planet to Earth. When you look at the planet you can appreciate the following time delay based on the standard unit of measure: Light from Sun: 8 minutes for 1 A.U. (Astronomical Unit = average Earth-Sun distance)
Light from planets reaches your telescope after traveling a distance measured in A.U units
- Mars 0.5 A.Us = 0.5 x 8 minutes = 4 minutes
- Jupiter 5.921 = ~6 x 8 minutes = 48 minutes
- Saturn 9.026 = ~9 x 8 minutes = 72 minutes
Planets were known as ‘wanderers’ to the Greeks. They move relative to Earth’s orbit around the Sun. We can only see them when their location in the ecliptic plane connects a line of sight Sun-Earth-Planet with direction away from the Sun. In this picture Venus would be hidden in the glare of the sun. However all the other sight lines to planets from Earth point away from the Sun. To learn more about planets and their orbits see Millstone Night Sky article Planets, Earth and Orbits around the Sun
