Tumbleweed Observatory's

Astronomy Hints




The Night Sky Displays From The Xephem Planetarium Program

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What's Up Tonight (01/21/2017) According To Xephem?

I don't know how to decide what to view on any given night, but when I get the amateur astronomy itch I sit down for a brief session with my favorite planetarium program Xephem. For me it has the right combination of utility, speed, and computer requirement.

These images show just some of the displays you can get from Xephem to help you plan your evening. Whether you want to know what stars are out, what Jupiter's moons are doing, or the phase of the Moon, these displays will tell you. You're welcome to use this web page as a quick evening reference, but you can plan even better if you just get Xephem. If you get xephem on you own computer, you can adjust the view for anywhere in the world, and step through time to see exactly when specific events will occur.

These displays are good for the evening of 01/21/2017. I've chosen Denver, Colorado as the viewing site, and the view at 9:00 PM Denver time. It seemed that it was a good median point of view, as Denver is centrally located in the U.S.

Tonight's Stars

This display, called the xephem Sky View, shows the position of the stars at any selected time. This image is small to make the web page load quickly, but with the Xephem program you can make it full screen.

You can also select different labels, and turn on display of deep space objects (galaxies, nebula, star clusters, etc.) from various almanacs, such as the Messier objects.

There are many other features in the actual Xephem live display. You can right click on an item and get information about it, such as alternate names for it, what type of object is it, or its magnitude.

When Do The Moon and Planets Rise?

The Xephem Data Table
Xephem Data Table

The Xephem At A Glance Table
Xephem At A Glance Table

The image above and left is the xephem Data Table display. It shows some handy information to help you plan your moon and planet observing sessions.

The table shows data for the Moon, Venus, Mars, Jupiter, and Saturn. The data listed shows each object's visual magnitude (VMag), Angular size in arc-seconds (Size), and 24 hour clock rise time (RisTm) and set time (SetTm) referenced to Denver Local Time.

While the sizes of the Moon, Jupiter and Saturn don't vary enormously, the same isn't true of Venus and Mars. Size doesn't mean a lot with Venus, as you won't be able to see details on it anyway, though you will be able to see the planet go through phases.

As to size, pay most attention to that of Mars. Mars can vary between about 4 arc-seconds is size, when on the other side of the sun from Earth, to 25 arc-seconds when in a most favorable opposition.

The image at upper right shows the xephem Night At A Glance table, which quickly indicates what items are visible at any time during the night. Night is indicated by the dark vertical bar, the gray regions being the daytime.

Where Are The Inner Planets Now?

The Xephem Solar System View

This xephem Solar System view shows where the inner planets are in their orbits with respect to one another. I reduced the scope of the diagram to only cover the inner planets since for observing considerations, their positions more more significant.

In this view the planets orbit in a counter-clockwise direction. A glance at this display will help you determine if the planets are going to be morning or evening objects (also see previous image), what the phases of Mecury and Venus will be, and whether or not Mars is near opposition.

The Phase Of The Moon

The Xephem Moon View

This is a very truncated version of the xephem Moon view. With the Xephem program you can set the size of the image, turn on labels of the Apollo landing sites, and select from a large list of lunar features which will then be labeled on the image.

This is the way the moon would appear to the naked eye.

The View Of Mars

The Xephem Mars Star Diagonal View
Star Diagonal View

The Xephem Mars Newtonian View
Newtonian View

These xephem Mars views show the appearance of Mars at the chosen time. The image to the left is a representation of Mars as viewed through a telescope using a star diagonal, such as a typical Cassegrain or refractor telescope. The view on the right is a representation of Mars as viewed through a Newtonian telescope. Though not visible in this reduced size image, the Xephem live display also shows the angular size of Mars, which varies considerably depending upon the relative positions of Earth and Mars.

This image, created using an alternate Xephem Mars map contributed by Bob Abraham, is a graphical representation of Mars with about a 0.5 arc-second limited view. Keep your eyes on it, as about every two years Mars and Earth come fairly close together, and the details become more clear.

For some Mars observing hints, visit Observing Mars.

For another indicator of what side of Mars is visible, check out the Sky and Telescope Mars Viewer.

The View Of Jupiter And Its Moons

The Xephem Jupiter View

I use this xephem Jupiter view feature of Xephem quite a bit. It shows the position of Jupiter's satellites at any given time, and will also show the Red Spot when in view.

I enjoy looking for the sometimes elusive Great Red Spot, and like especially to watch the moon shadows as they move across the face of Jupiter.

The moon labels are I=Io, II=Europa, III=Ganymede, and IV=Callisto.

This is a typical view through a telescope with a star diagonal. The planet rotates from right to left. The Observing Jupiter web page has some hints on how to observe Jupiter.

To find out when the Great Red Spot will transit, check out the Sky and Telescope GSR Applet.

The View Of Saturn, Its Moons, And Its Rings

The Xephem Saturn View

This xephem Saturn view display is also handy. It will show the inclination of Saturn's rings at the time chosen, and display the position of the moons of Saturn.

You can select the magnitude limit for the moons you wish displayed, and the field of view to consider. The display here shows a pretty large field of view to show the moon positions.

This is a typical view through a telescope with a star diagonal. The planet rotates from right to left.

Check out the Observing Saturn web page for some hints on observing the ringed giant.

This display shows only moons as bright as magnitude 13. The table below shows the moons' labels and typical magnitudes. Depending upon your seeing conditions and telescope size, you may not be able to see them all.