Earth and Moon ViewerCustom Request
Earth and Moon ViewerBy filling out the form below (presented in the same form as the Earth View Expert page) you can make a custom request with parameters preset. Then, after pressing the “Update” button to display the requested image, you can save the result as a “Favorite”, “Bookmark”, or whatever your browser calls it. Then you can immediately show your custom Earth View, updated to the current time (if you've selected “Now” as the Date/Time), just by selecting that item.
This is particularly handy for specifying the latitude and longitude for a view centred on your location, but you can use it to preset any parameter given below, including choosing a view from a satellite.
If you're unsatisfied with the result when you press “Update”, return to this page by pressing “Back” and adjust the parameters until you obtain the desired result, then save the request in your browser's favorite or bookmark list or copy and paste the link into a Web page of your own.
Normally, Earth and Moon Viewer generates an HTML page containing the requested view as an embedded image along with a control panel showing the parameters used to produce the image and permitting further requests. Suppose, instead, you wish to embed a custom image from Earth and Moon Viewer in a Web page of your own, for example, showing the current cloud cover above your home town, or the current phase of the Moon. To include custom, up-to-date images in a Web page, first use the form above to compose a Dynamic image request with the desired parameters. Enter the specifics of the image you require in the form, then press “Update” to preview the image. If you wish to further refine the image, return to this page with your browser's “Back” button (do not use the “Update” button in the result page, as that won't update the fields in the custom request), adjust the parameters, and repeat until you obtain the image you're looking for.
Then, return once again to this form with the “Back” button, check the “Dynamic image request” box in the Image: section, then press the “Update” button. You should obtain a page showing just the image, without the usual HTML page and control panel. More importantly, the URL or Address field in your browser's control panel will show a request which will reproduce the image on demand. You can copy the contents of this field and paste it into an <img> tag in your page to embed the requested image therein.
The request is dynamic in the sense that every time your page is displayed, Earth and Moon Viewer will supply an up-to-date image with the given parameters. If you've requested a view of the Earth with current cloud cover from the Sun, for example, the user will see current clouds on the illuminated hemisphere of the Earth at the moment your page is displayed, not at the time you made the request; the image is live, not canned. (Obviously, this applies only if the “Now” box is checked in the Date/Time: section of the form. If you specify a specific date and time, the image will be dynamically generated but invariant. If you prefer such an image [for example, the phase of the Moon on the day you were born], it's kinder on Earth and Moon Viewer and the Internet, not to mention much faster for visitors to your page, to simply save the image on your computer and embed it in your Web page as a regular local image.)
Let's consider a concrete example. Suppose you'd like to include an image of the Earth, with current cloud cover, as seen from the Moon, in a page advocating lunar exploration and development. In the form above, select “Current cloud cover” as the Image:, “Earth from Moon” as Viewpoint and Date/Time: of “Now”, checking “Dynamic image request” to obtain the image URL. After confirming that the image you obtained was what you intended, copy the request URL and include it in your Web page using HTML like the following:
<a href="https://www.fourmilab.ch/earthview/">
<img src="https://www.fourmilab.ch/cgi-bin/Earth?img=cloudy.bmp&imgsize=320&dynimg=y&opt=-m&date=0"
width="320" height="320"
alt="Earth from Moon: current cloud cover" />
</a>
(In the example above I have elided some blank parameters from the <img src= URL to shorten it and make the sample HTML more readable; including them as pasted from the dynamic image request will do no harm.) When you include such an image in your page, you should specify its size with width and height attributes and provide a textual description of the image with an alt attribute. The former allow your page to display more quickly while the dynamic image is generated; the latter provides an alternative for text-only browsers and screen reading programs used by the blind.
As in the example HTML above, when you link to a dynamic image, please link back to Earth and Moon Viewer so visitors to your page can see where the image came from and learn how to add such images to their own pages. If you neglect to provide this courtesy back-link, your premises may not be invaded by giant robot ants from Switzerland, but then you never know….
When requesting a view from an Earth satellite, the name of the satellite and its orbital elements are specified in the text box below the “From satellite” check box, with “From elements below” selected. For satellites in Earth and Moon Viewer's satellite database, you may simply specify the name: current orbital elements will be filled in automatically from the database. For satellites not in the database, you can paste the orbital elements in NASA/NORAD “two line element” format into the box, but this is a poor idea for dynamic views you intend to use for an extended period of time. Orbits of Earth satellites are specified as “osculating elements” which “kiss” the actual orbit only for a limited period of time around the date they are published. Even if a satellite's orbit doesn't change, out of date orbital elements will result in errors computing its position and show it in the incorrect location. Errors accumulate faster for satellites in low Earth orbit, but even geosynchronous satellites will eventually be shown at the wrong latitude if obsolete elements are used.
By specifying just the name of a satellite in Earth and Moon viewer's database, you're guaranteed up to date orbital elements will be used to compute its position; the database is updated daily from the Celestrak orbital element repository. For example, here's a request which shows the current view from one of the satellites in the Iridium constellation, specifying just the name to cause Earth and Moon Viewer to fetch its orbital elements from the database at the time of the request:
<a href="https://www.fourmilab.ch/earthview/">
<img src="https://www.fourmilab.ch/cgi-bin/Earth?img=learth.evif&imgsize=320&dynimg=y&opt=-b&bird=From+elements+below&tle=HST&date=0"
width="320" height="320"
alt="View from Hubble Space Telescope" />
</a>