What amazing views we have had in the evening sky! Of course, the weather we’ve had for the open houses has been horrible! Maybe we’ll get lucky this month.
Venus continues to brighten the evening sky, though its altitude is decreasing day by day. By the end of August it is setting at 9pm, about 90 minutes after sunset. By this time, Venus is setting in the evening twilight. Venus reaches its greatest separation from the Sun on August 17th but this is misleading. Yes, Venus is nearly five fists from the Sun’s brilliance but the orientation of the orbit is making a very small angle to the horizon. In other words, that “nearly five fists” is left of the Sun and not down to the horizon. Telescopically, Venus starts to get interesting as it swings closer to the Earth. Its brightness will in-crease to magnitude -4.6 and it’s illumination goes from 57% to 40% this month. Keep in mind 50% illumination would look like a mini-first quarter Moon. A thin crescent Moon is right of Venus on the evening of the 13th and is above Venus the next night. Venus continues to move to the left, along the horizon, until it is a degree below the star Spica on the 31st.
Venus and Jupiter will seem to approach each other but they won’t meet. Venus begins to head back towards the Sun at the end of August. Jupiter seems to skim over the top of the star Zubenelgenubi around the 16th, about the same time a nearly first quarter Moon passes over the pair. As the Earth pulls away from Jupiter, it appears to shrink and fade in brightness a little bit. Jupiter reaches “quadrature” on August 6th, meaning a line drawn from the Sun to the Earth and then Earth to Jupiter makes a 90 degree angle. So you might see Jupiter’s moons bob into and out of its large shadow. Jupiter sets at about 11:15pm in mid-August.
Saturn is next, sitting atop the lid of our Teapot in the south. Saturn is due south as the twilight starts to dim. Use binoculars and see if you can see the Lagoon Nebula near Saturn. With the rings tilted at 26 degrees, it’s a wonderful show! A waxing gibbous Moon is above and right of Jupiter on the 20th.
Lastly, we have Mars, fresh off its July 27 opposition date. I hope you can join us for our “Marswatch” on August 3 at Meadowbrook Park in Urbana. If you haven’t seen Mars yet you haven’t been looking. It’s brilliant in the southeast at magnitude -2.8. It’ll fade a bit this month but it’s still brighter than we usually see it. Though we’ll start to pull away from Mars, we will get good views the entire month. The higher Mars is in the sky, the better it will look and it crosses the meridian at 12:30am in early August and then 10:30pm late in the month. This month the apparent disk of Mars shrinks from 24 arc seconds to 21 arc seconds. We didn’t seem much detail at the July open house through the 16-inch dome telescope. Some of that is the global dust storm on the planet and some of it is the thick atmosphere of our Earth that we have to look through. Mars ends its retrograde motion on August 28 and begins to head back eastward in front of the background stars.
We’ll give a tip of the cap to Mercury, too, as it has probably its best morning view for 2018. Early risers should start looking at mid-month nearly due east. Greatest separation from the Sun occurs on the 26th when Mercury rises just before 5am (CDT). It is situated in the relatively star-poor constellation of Cancer.
The Perseid Meteor Shower peaks every August during the morning hours of August 12 and 13. The Perseids are one of two of the year’s best showers (the other being in December) and we’re in luck this year as 1) they happen during New Moon and 2) it’s a weekend! Typically one sees a meteor or two a minute during peak hours under dark skies. We’ll talk about the Perseids at the August 9th meeting and at the Homer Lake Forest Preserve on the 11th.
Have you heard about Comet PanSTARRS? If you’ve heard that name, PanSTARRS is an acronym for a survey telescope which has discovered several comets. This one (C/2017 S3) went through several outbursts in mid-July. On July 16th it was at magnitude 8.2 and seen in 10×50 binoculars in a dark sky. By the time you read this, how bright will the comet be? Some estimates have it reaching magnitude 3 or 4 but you never know. At the end of July it was located in northeastern Auriga in the northeastern sky (or below and left of Capella with re-spect to the horizon), which means you’ll need to look around 1-2am. It is expected to cruise north of the Gemini twins. Look before August 8 as perihelion is the 15th. Comet Giacobini-Zinner is also expected to brighten to possibly magnitude 7 this month. It is in the vicinity of Cassiopeia. For charts and orbits, try going to https://theskylive.com/comets which is a very cool web site (but remember to change your observing location).