• Luke

If you have been out at dusk lately You may be noticing the brightest star that appears over the southern horizon just after sunset. This “star” is actually the planet Jupiter!



Infrared view of 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 earth's inside Jupiter. Being so massive has made Jupiter a solar system within our solar system, as it's extreme gravitational pull captures lots of objects as moons of Jupiter.



Jupiter's size compared to earth, the entirety of earth could fit, with room to spare, in Jupiter's 'great red spot' (an acid hurricane that has been raging on Jupiter for centuries)

Jupiter currently has 79 known moons. This number keeps increasing as recently as July of 2018, we added 10 newly discovered moons to the total. 26 of the moons are so new they are still awaiting official names. We are not done adding to the number of known moons of Jupiter. Astronomers are discovering new moons of Jupiter so frequently the main trick has become making sure the newly observed moons are not the same as a moon we have previously counted.


The number of moons of Jupiter will also be changing further as new moons are likely about to be made and destroyed. Of the known objects going around Jupiter most are going the same direction but, some are going the opposite direction and just like if you go the opposite direction of traffic in a traffic circle collision is likely.

If you look at Jupiter with even just a halfway 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 but, telling which one is which takes several observations over a long 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. (or you can just cheat and use this web tool)



how Jupiter and it's 4 Galilean Moons appear in a telescope or binoculars (the stripes/spot can be much harder to see than it might look from this picture)to


All of the Galilean Moons are interesting places and studied extensively. Io (the closest) is the most volcanic body in our solar system, Eropa 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.

Jupiter’s moons served as one of the first standardized clocks. Jupiter’s moons movement is regular and predictable so the Royal Observatory in Greenwich calculated and published their future locations and local time (as would be shown on a sundial or pendulum clock) at Greenwich, forming the foundations for our time zones based around Greenwich Mean Time.

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.


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. This has been the only silver lining of stargazing in Colorado thru the smog/haze from the wild fires in the mountains is that the haze has been increasing the contrast on Jupiter making the stripes and spot easier to see (I've actually been able to make out a personal record number of stripes this year seeing 7). A day on Jupiter last 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.



close up of the spot on Jupiter


Jupiter is currently “in Capricorn ”. Capricorn doesn't look like much unless you have really dark sky, but you will see Sagittarius to the right, right next to it! If you have decently dark skies and some imagination you might see a constellation that resembles a teapot just to the right of Jupiter. A triangular lid atop a trapezoidal body with a trapezoidal handle on the east side and a triangular spout on the west side. Even better if you are in a particularly dark area you can see the milky way appearing as steam coming out of the spout. This “teapot” was originally seen as an archer, and named Sagittarius. The tip of the spout to the two stars that make the top of the handle are the arrow and the top of the lid and the two stars to the right of the base make the bow for the archer.


The archer's arrow is drawn pointing to the west towards a bright star with a red/orange hue. This star is Antares. Antares is not to be confused with mars which is currently rising in the eastern sky around 10pm ~ish (this is such a common mistake it is where Antares name came from, it's Arabic for 'rival of mars'). The star Antares is the heart of the scorpion or Scorpio. and Sagittarius is protecting others from Scorpio by keeping his bow drawn towards it's heart.

Capricorn, Sagittarius, and Scorpio you might be familiar with from the zodiac over the course of 12 years we can watch Jupiter move across every sign in the zodiac. If you read my post on Jupiter two years ago you have been able to watch Jupiter move from the constellation Scorpio to the next constellation in the zodiac Sagittarius and now to Capricorn! Jupiter takes just a little less than 12 years to go around the Sun, there are 12 signs in the zodiac, therefore Jupiter spends a year in each one! so next year we can be sure to find Jupiter in Aquarius!



Come get a closer look at Jupiter seeing it's stripes (this year better than ever with the haze), moons, red spot and more! On an astronomy tour! Book now for an out of this world experience!

  • Luke

AstroTours.org is committed to becoming an anti-racist organization. We mourn the murder of George Floyd and all victims of racial injustice and police brutality. Black Lives Matter. We stand in solidarity with protests across the nation and globally calling for justice and accountability.



Juneteenth parade Denver

The Night Sky is a common heritage of all cultures and peoples. The stars have played an integral part throughout history in both guiding oppressors to the lands of peaceful peoples (from Columbus to Cook) and in guiding oppressed peoples to liberation (from the underground railroad to the Jews of Egypt). We try to include these stories but In all sincerity, the current situation made us take a hard look at the voices within our organization and we realized that we have a lot of work to do.


We are a white-led organization with a white staff, and have a majority-white audience. We conduct tours upon the occupied lands of the Southern Arapaho people. We are a part of the scientific community that has been and continues to be exploitative of people of color. We're also part of an education system that has centered and valued the contributions and expertise of white people above those of Black people and people of color. Beyond this, we are living through a global pandemic that is having an outsized impact on people of color.


AstroTours.org has not been exempt from these patterns of injustice, and in fact we have benefited from our position of privilege. We acknowledge this, and know that we have much work to do. We also acknowledge that this statement itself is late in coming, and is insufficient on its own.


We are learning and listening, with particular attention to Black, Indigenous, People of Color voices in our community. We are working on creating pathways forward to further center and uplift these voices as we work towards becoming an anti-racist organization.

  • Luke

Updated: Aug 14

Our astronomy tours at the boulder valley ranch trailhead are currently opening back up! June 14th will mark our first tour since the shutdown.

We are looking to phase back into business slowly making sure we do so safely and adhering to Colorado’s “safer at home order” Astro Tours is a much lower risk activity than most events and public spaces that are currently being opened.


Our tours take place outside with plenty of room to distance. There is no contact between guests as we are adamant that no one touches the delicate equipment and telescopes. We provide hand sanitizer and disinfecting wipes on all of our tours which guests are requested to use frequently.


We are introducing steps beyond those listed above to help protect our guests and staff such as:

  • We will no longer serve Tea or Cookies on the tour instead offering only pre-packaged granola bars and chips.

  • We are limiting the numbers of guests to fewer than 10 people every tour.

  • We disinfect all seats and equipment before and after tours.

  • We always have offered refunds/free-cancellations for any reason but, we are taking this further by refunding and telling guests; Do not come if you have been in contact with anyone who was sick or are feeling sick yourself. We are offering free cancellations to these people as well as: anyone who has changed travel plans/amino compromised/do not feel safe attending/or for any reason at all.

  • We are spacing telescopes and chairs further apart and setting out extra chairs so groups can separate with a few chairs between them. Please try to maintain a 6ft distance from others.

  • We require all guests to wear a mask at all times that they are not able to stay 6ft apart from staff and other guests. while seated or away from anyone else feel free to lower your mask to eat/drink but masks are required when less than 6ft from others which can happen during transitions between telescopes, etc.

  • Please be respectful and take all precautions possible to maintain your's and everyone else's health and safety.


We will continue these and any other practices recommended by the city, state, CDC, staff, and guests for as long as necessary to be sure that COVID is not spreading at our tours.


Because of the limited selection at the tea table and to show our gratitude to all of our guests that are sticking with us during this time we are offering tours at a $5 discount. Food/drink is still aloud so feel free to use this savings to stop by one of Boulder's many local tea/coffee shops and bring a warm drink on the tour. Thank you for your continued support, stay safe and hope to see you soon.


For more information on protecting yourself and others please visit: https://www.cdc.gov/coronavirus/2019-nCoV/index.html


For Information specific to boulder and what our community is doing to help please visit:

https://bouldercolorado.gov/coronavirus