The Planets
Planet Data For September
Click on any planet below to go straight to its section.
The table below shows key data for the planets this month, including rise, transit and set times, as well as magnitude, apparent size and position data (right ascension and declination).
Events that occur when the sun is below the horizon are shown with a black background and white text. All other events happen when the sun is in the sky and other for not visible for observation.
September is a great month for planet-watching, because we get to enjoy the gas giants Jupiter and Saturn during our evening observation sessions once again.
On top of that, we can enjoy both Mercury and Venus in the morning, if we’re prepared to be outside before the sun rises. Mars, though, is finally lost to our view because it moves too close to the sun.
If you relish a challenge, this month might be a great time to track down our most distant neighbors, Uranus and Neptune, both of which ride high in the middle of the night.
All of the images below can be opened full screen in a new tab by clicking on them
Mercury
05th September
The closest planet to the sun is so close that we’re not able to see it at the moment. This is where it is just before sunrise.
15th September
Very soon afterwards, we see that Mercury has pulled away from the sun. This is the view at 6:30 and Mercury is 7° high.
25th September
At the same time ten days later, Mercury is 9° high in the east. It’s shining at magnitude -0.7 and its disc is two-thirds lit.
It feels like a long time since we’ve had the chance to take a decent look at Mercury, but the second half of September gives us that chance.
Mercury is a morning planet this month and, by the middle of September, is high enough in the east before sunrise that we’ll be able to view it with our telescopes. As the month goes on, you can see that Mercury gets brighter, its magnitude growing from +1.1 on the 15th (see table above) to -1.0 two weeks later. At the same time, however, the planet is getting further away from us: we can see its disc shrink from 8.7 arcseconds to 5.7 over the same two weeks.
So, what’s going on here? How is the planet getting brighter as its disc gets smaller?
Well, just like the moon, the disc of Mercury has phases. At the start of September, it will be relatively close to Earth, i.e. it’ll have a large disc, but it will also just passed in front of the sun, so most of the disc will be dark, like a new moon. As it moves around the sun, the disc gets smaller, because it’s moving away from us, but more of it is lit, which is what makes it brighter.
On the first of the month, Mercury’s disc is only 5% lit. As the the last day of September arrives, we’ll see that 80% of the tiny disc is illuminated.
Venus
05th September
Once more a bright morning planet, we can see Venus high in the east before sunrise. This is the view at 6:30 am.
15th September
At 6:00 am, the sun is having less of an influence on the sky’s brightness and we can see 22° high and only 1/4 lit.
25th September
6:00 am today is fully an hour before sunrise, so we’ll have a properly dark sky to see this bright planet now 1/3rd illuminated.
Venus makes its presence felt as a bright morning planet this month. Like Mercury, it too recently passed in front of the sun and is now heading away from us on its journey around our star.
Over the course of September, we’ll observe this as the planetary disc shrinking, from 49 to 32 arcseconds, while brightening as the proportion of the disc that is lit increases from 12% to 36%.
To see it, we’ll need some early starts. It’s best viewed before the sky starts to brighten, which means about 6 am this month.
Mars
05th September
Just minutes after sunset, at 8 pm, we see the dot that is Mars low in the west. The planet is out of reach of our scopes now.
15th September
This scene is also 8 pm and we can see that Mars is setting, just a few minutes behind the sun.
25th September
We see events at 7:30 pm in this image.
The Red Planet has finally moved out of sight. This month, it’s moving so close to the sun that we’ll no longer be able to see it with our telescopes.
There are still a few weeks to go before Mars’s superior conjunction. It passes behind our star on 17 November, after which, it’ll become a morning planet again.
Sadly, there is not much to see through our telescopes on the Martian surface before the last half of 2024, and we won’t even see the planet itself until spring 2024 is knocking on the door.
Jupiter
05th September
Jupiter is still technically a morning planet but this view at 11:30 pm shows that we can see it in as part of an evening session now.
15th September
At the same time, we can now see Jupiter over 20° high in the east.
25th September
This chart shows the view at 11 pm. Jupiter is 47 arcseconds wide and 23° high in the east.
By the end of September, Jupiter rises before 9 pm and offers useful viewing before ten o’clock, which is great news for us evening observers, after months of it being only accessible to early-risers.
Not much changes this month. We’ll see the disc get slightly larger as we move closer to this gas giant. The best views of the year are only a few weeks away now though, as Jupiter reaches opposition on 02 November.
Saturn
05th September
Also a comfortable evening object now, Saturn is at its highest at 1 am, but this is the view at 11 pm, when it’s 34° high in the southeast.
15th September
Almost due south – which is where the ringed planet will transit – this view at 11 pm shows it 37° high.
25th September
An earlier view now, this time 10 pm, showing Saturn in almost the same place as it was ten days ago.
Saturn reached opposition at the end of last month and is now, officially, an evening object.
It’s as large and bright as it gets this year at the moment, with its disc of 19 arcseconds across and shining at magnitude 0.4. It’s easy to track down in Aquarius, being one of the brightest ‘stars’ when you look south. It’s about 40° high at its highest, which is roughly midway between the horizon and overhead.
Uranus & Neptune
15th September – Uranus
Uranus is close to Jupiter in the middle of the month, making for a good marker to help track it down. This is the view at 3 am looking southeast.
15th September – Neptune
Just after midnight, Neptune is 44° high in the southeast, strung out between Saturn and Jupiter.
These two ice giants are visible this month, if not at especially sociable hours. We can use Jupiter to help track Uranus down, but Neptune requires a more dedicated search.
All Planets Viewer
Use the table below to see when each of the planets is observable for each day this month. Click on it for full screen.
A planet is classed as observable when it is more than 10° above the horizon and the sky is dark enough for it to be observed.
Planet ephemeris tables produced with the kind permission of Dominic Ford. Sky images are courtesy of SkySafari Pro 6.