The NPR news article and podcast New Telescope Promises To Revolutionize Astronomy updates the status of the "Large Synoptic Survey Telescope under construction on Cerro Pachón in Chile".

NPR's Joe Palca's piece includes sound bites from astronomers, including Caltech astronomer Mansi Kasliwal:

PALCA: Kasliwal says although LSST will detect these events, other telescopes are better suited to study them in detail. So the plan is to send out an alert to other telescopes when LSST sees something interesting. Of course, that means the other telescope has to drop what it was doing, but Kasliwal says it will be worth it.

Isn't the LSST expected to "see something interesting" quite often?

Due to the size and scope of LSST's surveying capability which is due to it's huge corrected field of view and huge focal plane array and huge image processing and event detection capacity, there is a potential for a significant increase in the rate of alerts generated and sent to observatories and to astronomers' cell phones (one notable example of such things).

Question: Will LSST make a significant increase in the rate of astronomical event alerts? Has there been an estimate of how the overall rate will change when it comes online?

I'm wondering if astronomers will get woken up more often by their phones, or if some observatories will have to make the decision to promptly change observing schedules or not much more frequently.

  • $\begingroup$ @buzjwa thanks for the edit! It looks like the spelling has been fixed on the NPR site as well. $\endgroup$
    – uhoh
    Sep 11, 2019 at 22:26

1 Answer 1


Yes. The estimates are that LSST will produce about 10 million alerts per night (LSST Alert Distribution presentation) which will be at least a factor of 5x greater than the amount coming from ZTF currently. ZTF is an approximately 10% scale model of what the LSST alert stream will look as there is about 5x fewer alerts and the alert packets contain about 50-60% of the information that will be in the LSST alerts. The ZTF alert stream (Patterson et al. 2019) also uses the same software (Apache Avro, Spark and Kafka) as LSST will use, just running on less hardware.

These alerts (in Avro serialized binary data format) will not be sent directly to astronomers (and certainly not to cell phones), the plan is to send the alerts to a few "brokers" that will do additional filtering, classification and cross-matching to other catalogs to give additional information and context to the alert (which is basically a "this source on the sky changed in brightness by X amount or appeared"). There are several brokers in various stages of development of which the leading examples are ANTARES and Lasair.

Astronomers, or more likely their software systems, will subscribe to these brokers and add filters for the alerts to subset the stream down to the particular types of objects and science that interest them. These will most likely go into their own databases of interesting targets and astronomers or their software will decide on the small number of most interesting ones that will be sent out to other telescopes, some robotic for rapid response science case, some traditionally scheduled. The large number of alerts and triggers for follow-up has the potential to be very disruptive to the prior way of operating observatories, which is one of the reasons why we are working on system like the Astronomical Event Observatory Network (AEON) to handle and coordinate this.

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    $\begingroup$ thanks for the speedy yet thorough and well-sourced answer! $\endgroup$
    – uhoh
    Jul 25, 2019 at 6:12
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    $\begingroup$ I've created an alerts but when you mention millions per night and the "brokers" I wonder if that is the best choice for the tag's name. I think it works okay for for most people, but could it be considered the wrong term to use in the astronomical community? $\endgroup$
    – uhoh
    Jul 25, 2019 at 6:13
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    $\begingroup$ Some of the astronomical community don't like the name "broker" either... ;-) You could use "event broker" but it seems premature to be making tags at this stage. The general ecosystem of surveys providing near real-time alerts for rapid follow-up is called "time domain astronomy" which might be worth a tag (but is a bit long). Move discussion to meta ? $\endgroup$ Jul 25, 2019 at 15:29
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    $\begingroup$ Targets of opportunity (ToOs) $\endgroup$
    – ProfRob
    Jul 25, 2019 at 15:33

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